zf

repo.ex (74306B)

---

 defmodule Ecto.Repo do
   @moduledoc """
   Defines a repository.
 
   A repository maps to an underlying data store, controlled by the
   adapter. For example, Ecto ships with a Postgres adapter that
   stores data into a PostgreSQL database.
 
   When used, the repository expects the `:otp_app` and `:adapter` as
   option. The `:otp_app` should point to an OTP application that has
   the repository configuration. For example, the repository:
 
       defmodule Repo do
         use Ecto.Repo,
           otp_app: :my_app,
           adapter: Ecto.Adapters.Postgres
       end
 
   Could be configured with:
 
       config :my_app, Repo,
         database: "ecto_simple",
         username: "postgres",
         password: "postgres",
         hostname: "localhost"
 
   Most of the configuration that goes into the `config` is specific
   to the adapter. For this particular example, you can check
   [`Ecto.Adapters.Postgres`](https://hexdocs.pm/ecto_sql/Ecto.Adapters.Postgres.html)
   for more information. In spite of this, the following configuration values
   are shared across all adapters:
 
     * `:name`- The name of the Repo supervisor process
 
     * `:priv` - the directory where to keep repository data, like
       migrations, schema and more. Defaults to "priv/YOUR_REPO".
       It must always point to a subdirectory inside the priv directory
 
     * `:url` - an URL that specifies storage information. Read below
       for more information
 
     * `:log` - the log level used when logging the query with Elixir's
       Logger. If false, disables logging for that repository.
       Defaults to `:debug`
 
     * `:pool_size` - the size of the pool used by the connection module.
       Defaults to `10`
 
     * `:telemetry_prefix` - we recommend adapters to publish events
       using the `Telemetry` library. By default, the telemetry prefix
       is based on the module name, so if your module is called
       `MyApp.Repo`, the prefix will be `[:my_app, :repo]`. See the
       "Telemetry Events" section to see which events we recommend
       adapters to publish. Note that if you have multiple databases, you
       should keep the `:telemetry_prefix` consistent for each repo and
       use the `:repo` property in the event metadata for distinguishing
       between repos.
 
     * `:stacktrace`- when true, publishes the stacktrace in telemetry events
       and allows more advanced logging.
 
   ## URLs
 
   Repositories by default support URLs. For example, the configuration
   above could be rewritten to:
 
       config :my_app, Repo,
         url: "ecto://postgres:postgres@localhost/ecto_simple"
 
   The schema can be of any value. The path represents the database name
   while options are simply merged in.
 
   URL can include query parameters to override shared and adapter-specific
   options, like `ssl`, `timeout` and `pool_size`. The following example
   shows how to pass these configuration values:
 
       config :my_app, Repo,
         url: "ecto://postgres:postgres@localhost/ecto_simple?ssl=true&pool_size=10"
 
   In case the URL needs to be dynamically configured, for example by
   reading a system environment variable, such can be done via the
   `c:init/2` repository callback:
 
       def init(_type, config) do
         {:ok, Keyword.put(config, :url, System.get_env("DATABASE_URL"))}
       end
 
   ## Shared options
 
   Almost all of the repository functions outlined in this module accept the following
   options:
 
     * `:timeout` - The time in milliseconds (as an integer) to wait for the query call to
       finish. `:infinity` will wait indefinitely (default: `15_000`)
     * `:log` - When false, does not log the query
     * `:telemetry_event` - The telemetry event name to dispatch the event under.
       See the next section for more information
     * `:telemetry_options` - Extra options to attach to telemetry event name.
       See the next section for more information
 
   ## Telemetry events
 
   There are two types of telemetry events. The ones emitted by Ecto and the
   ones that are adapter specific.
 
   ### Ecto telemetry events
 
   The following events are emitted by all Ecto repositories:
 
     * `[:ecto, :repo, :init]` - it is invoked whenever a repository starts.
       The measurement is a single `system_time` entry in native unit. The
       metadata is the `:repo` and all initialization options under `:opts`.
 
   ### Adapter-specific events
 
   We recommend adapters to publish certain `Telemetry` events listed below.
   Those events will use the `:telemetry_prefix` outlined above which defaults
   to `[:my_app, :repo]`.
 
   For instance, to receive all query events published by a repository called
   `MyApp.Repo`, one would define a module:
 
       defmodule MyApp.Telemetry do
         def handle_event([:my_app, :repo, :query], measurements, metadata, config) do
           IO.inspect binding()
         end
       end
 
   Then, in the `Application.start/2` callback, attach the handler to this event using
   a unique handler id:
 
       :ok = :telemetry.attach("my-app-handler-id", [:my_app, :repo, :query], &MyApp.Telemetry.handle_event/4, %{})
 
   For details, see [the telemetry documentation](https://hexdocs.pm/telemetry/).
 
   Below we list all events developers should expect from Ecto. All examples
   below consider a repository named `MyApp.Repo`:
 
   #### `[:my_app, :repo, :query]`
 
   This event should be invoked on every query sent to the adapter, including
   queries that are related to the transaction management.
 
   The `:measurements` map will include the following, all given in the
   `:native` time unit:
 
     * `:idle_time` - the time the connection spent waiting before being checked out for the query
     * `:queue_time` - the time spent waiting to check out a database connection
     * `:query_time` - the time spent executing the query
     * `:decode_time` - the time spent decoding the data received from the database
     * `:total_time` - the sum of (`queue_time`, `query_time`, and `decode_time`)️
 
   All measurements are given in the `:native` time unit. You can read more
   about it in the docs for `System.convert_time_unit/3`.
 
   A telemetry `:metadata` map including the following fields. Each database
   adapter may emit different information here. For Ecto.SQL databases, it
   will look like this:
 
     * `:type` - the type of the Ecto query. For example, for Ecto.SQL
       databases, it would be `:ecto_sql_query`
     * `:repo` - the Ecto repository
     * `:result` - the query result
     * `:params` - the query parameters
     * `:query` - the query sent to the database as a string
     * `:source` - the source the query was made on (may be `nil`)
     * `:stacktrace` - the stacktrace information, if enabled, or `nil`
     * `:options` - extra options given to the repo operation under
       `:telemetry_options`
 
   ## Read-only repositories
 
   You can mark a repository as read-only by passing the `:read_only`
   flag on `use`:
 
       use Ecto.Repo, otp_app: ..., adapter: ..., read_only: true
 
   By passing the `:read_only` option, none of the functions that perform
   write operations, such as `c:insert/2`, `c:insert_all/3`, `c:update_all/3`,
   and friends will be defined.
   """
 
   @type t :: module
 
   @doc """
   Returns all running Ecto repositories.
 
   The list is returned in no particular order. The list
   contains either atoms, for named Ecto repositories, or
   PIDs.
   """
   @spec all_running() :: [atom() | pid()]
   defdelegate all_running(), to: Ecto.Repo.Registry
 
   @doc false
   defmacro __using__(opts) do
     quote bind_quoted: [opts: opts] do
       @behaviour Ecto.Repo
 
       {otp_app, adapter, behaviours} =
         Ecto.Repo.Supervisor.compile_config(__MODULE__, opts)
 
       @otp_app otp_app
       @adapter adapter
       @default_dynamic_repo opts[:default_dynamic_repo] || __MODULE__
       @read_only opts[:read_only] || false
       @before_compile adapter
       @aggregates [:count, :avg, :max, :min, :sum]
 
       def config do
         {:ok, config} = Ecto.Repo.Supervisor.runtime_config(:runtime, __MODULE__, @otp_app, [])
         config
       end
 
       def __adapter__ do
         @adapter
       end
 
       def child_spec(opts) do
         %{
           id: __MODULE__,
           start: {__MODULE__, :start_link, [opts]},
           type: :supervisor
         }
       end
 
       def start_link(opts \\ []) do
         Ecto.Repo.Supervisor.start_link(__MODULE__, @otp_app, @adapter, opts)
       end
 
       def stop(timeout \\ 5000) do
         Supervisor.stop(get_dynamic_repo(), :normal, timeout)
       end
 
       def load(schema_or_types, data) do
         Ecto.Repo.Schema.load(@adapter, schema_or_types, data)
       end
 
       def checkout(fun, opts \\ []) when is_function(fun) do
         %{adapter: adapter} = meta = Ecto.Repo.Registry.lookup(get_dynamic_repo())
         adapter.checkout(meta, opts, fun)
       end
 
       def checked_out? do
         %{adapter: adapter} = meta = Ecto.Repo.Registry.lookup(get_dynamic_repo())
         adapter.checked_out?(meta)
       end
 
       @compile {:inline, get_dynamic_repo: 0, prepare_opts: 2}
 
       def get_dynamic_repo() do
         Process.get({__MODULE__, :dynamic_repo}, @default_dynamic_repo)
       end
 
       def put_dynamic_repo(dynamic) when is_atom(dynamic) or is_pid(dynamic) do
         Process.put({__MODULE__, :dynamic_repo}, dynamic) || @default_dynamic_repo
       end
 
       def default_options(_operation), do: []
       defoverridable default_options: 1
 
       defp prepare_opts(operation_name, opts) do
         operation_name
         |> default_options()
         |> Keyword.merge(opts)
       end
 
       ## Transactions
 
       if Ecto.Adapter.Transaction in behaviours do
         def transaction(fun_or_multi, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Transaction.transaction(__MODULE__, repo, fun_or_multi, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:transaction, opts)))
         end
 
         def in_transaction? do
           Ecto.Repo.Transaction.in_transaction?(get_dynamic_repo())
         end
 
         @spec rollback(term) :: no_return
         def rollback(value) do
           Ecto.Repo.Transaction.rollback(get_dynamic_repo(), value)
         end
       end
 
       ## Schemas
 
       if Ecto.Adapter.Schema in behaviours and not @read_only do
         def insert(struct, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.insert(__MODULE__, repo, struct, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:insert, opts)))
         end
 
         def update(struct, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.update(__MODULE__, get_dynamic_repo(), struct, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:update, opts)))
         end
 
         def insert_or_update(changeset, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.insert_or_update(__MODULE__, get_dynamic_repo(), changeset, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:insert_or_update, opts)))
         end
 
         def delete(struct, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.delete(__MODULE__, get_dynamic_repo(), struct, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:delete, opts)))
         end
 
         def insert!(struct, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.insert!(__MODULE__, get_dynamic_repo(), struct, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:insert, opts)))
         end
 
         def update!(struct, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.update!(__MODULE__, get_dynamic_repo(), struct, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:update, opts)))
         end
 
         def insert_or_update!(changeset, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.insert_or_update!(__MODULE__, get_dynamic_repo(), changeset, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:insert_or_update, opts)))
         end
 
         def delete!(struct, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.delete!(__MODULE__, get_dynamic_repo(), struct, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:delete, opts)))
         end
 
         def insert_all(schema_or_source, entries, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Schema.insert_all(__MODULE__, get_dynamic_repo(), schema_or_source, entries, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:insert_all, opts)))
         end
       end
 
       ## Queryable
 
       if Ecto.Adapter.Queryable in behaviours do
         if not @read_only do
           def update_all(queryable, updates, opts \\ []) do
             repo = get_dynamic_repo()
             Ecto.Repo.Queryable.update_all(get_dynamic_repo(), queryable, updates, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:update_all, opts)))
           end
 
           def delete_all(queryable, opts \\ []) do
             repo = get_dynamic_repo()
             Ecto.Repo.Queryable.delete_all(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:delete_all, opts)))
           end
         end
 
         def all(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.all(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def stream(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.stream(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:stream, opts)))
         end
 
         def get(queryable, id, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.get(get_dynamic_repo(), queryable, id, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def get!(queryable, id, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.get!(get_dynamic_repo(), queryable, id, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def get_by(queryable, clauses, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.get_by(get_dynamic_repo(), queryable, clauses, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def get_by!(queryable, clauses, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.get_by!(get_dynamic_repo(), queryable, clauses, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def reload(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.reload(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:reload, opts)))
         end
 
         def reload!(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.reload!(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:reload, opts)))
         end
 
         def one(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.one(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def one!(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.one!(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def aggregate(queryable, aggregate, opts \\ [])
 
         def aggregate(queryable, aggregate, opts)
             when aggregate in [:count] and is_list(opts) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.aggregate(get_dynamic_repo(), queryable, aggregate, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def aggregate(queryable, aggregate, field)
             when aggregate in @aggregates and is_atom(field) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.aggregate(get_dynamic_repo(), queryable, aggregate, field, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, [])))
         end
 
         def aggregate(queryable, aggregate, field, opts)
             when aggregate in @aggregates and is_atom(field) and is_list(opts) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.aggregate(get_dynamic_repo(), queryable, aggregate, field, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def exists?(queryable, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Queryable.exists?(get_dynamic_repo(), queryable, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:all, opts)))
         end
 
         def preload(struct_or_structs_or_nil, preloads, opts \\ []) do
           repo = get_dynamic_repo()
           Ecto.Repo.Preloader.preload(struct_or_structs_or_nil, get_dynamic_repo(), preloads, Ecto.Repo.Supervisor.tuplet(repo, prepare_opts(:preload, opts)))
         end
 
         def prepare_query(operation, query, opts), do: {query, opts}
         defoverridable prepare_query: 3
       end
     end
   end
 
   ## User callbacks
 
   @optional_callbacks init: 2
 
   @doc """
   A callback executed when the repo starts or when configuration is read.
 
   The first argument is the context the callback is being invoked. If it
   is called because the Repo supervisor is starting, it will be `:supervisor`.
   It will be `:runtime` if it is called for reading configuration without
   actually starting a process.
 
   The second argument is the repository configuration as stored in the
   application environment. It must return `{:ok, keyword}` with the updated
   list of configuration or `:ignore` (only in the `:supervisor` case).
   """
   @doc group: "User callbacks"
   @callback init(context :: :supervisor | :runtime, config :: Keyword.t()) ::
               {:ok, Keyword.t()} | :ignore
 
   ## Ecto.Adapter
 
   @doc """
   Returns the adapter tied to the repository.
   """
   @doc group: "Runtime API"
   @callback __adapter__ :: Ecto.Adapter.t()
 
   @doc """
   Returns the adapter configuration stored in the `:otp_app` environment.
 
   If the `c:init/2` callback is implemented in the repository,
   it will be invoked with the first argument set to `:runtime`.
   """
   @doc group: "Runtime API"
   @callback config() :: Keyword.t()
 
   @doc """
   Starts any connection pooling or supervision and return `{:ok, pid}`
   or just `:ok` if nothing needs to be done.
 
   Returns `{:error, {:already_started, pid}}` if the repo is already
   started or `{:error, term}` in case anything else goes wrong.
 
   ## Options
 
   See the configuration in the moduledoc for options shared between adapters,
   for adapter-specific configuration see the adapter's documentation.
   """
   @doc group: "Runtime API"
   @callback start_link(opts :: Keyword.t()) ::
               {:ok, pid}
               | {:error, {:already_started, pid}}
               | {:error, term}
 
   @doc """
   Shuts down the repository.
   """
   @doc group: "Runtime API"
   @callback stop(timeout) :: :ok
 
   @doc """
   Checks out a connection for the duration of the function.
 
   It returns the result of the function. This is useful when
   you need to perform multiple operations against the repository
   in a row and you want to avoid checking out the connection
   multiple times.
 
   `checkout/2` and `transaction/2` can be combined and nested
   multiple times. If `checkout/2` is called inside the function
   of another `checkout/2` call, the function is simply executed,
   without checking out a new connection.
 
   ## Options
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
   """
   @doc group: "Transaction API"
   @callback checkout((() -> result), opts :: Keyword.t()) :: result when result: var
 
   @doc """
   Returns true if a connection has been checked out.
 
   This is true if inside a `c:Ecto.Repo.checkout/2` or
   `c:Ecto.Repo.transaction/2`.
 
   ## Examples
 
       MyRepo.checked_out?
       #=> false
 
       MyRepo.transaction(fn ->
         MyRepo.checked_out? #=> true
       end)
 
       MyRepo.checkout(fn ->
         MyRepo.checked_out? #=> true
       end)
 
   """
   @doc group: "Transaction API"
   @callback checked_out?() :: boolean
 
   @doc """
   Loads `data` into a schema or a map.
 
   The first argument can be a a schema module or a map (of types).
   The first argument determines the return value: a struct or a map,
   respectively.
 
   The second argument `data` specifies fields and values that are to be loaded.
   It can be a map, a keyword list, or a `{fields, values}` tuple.
   Fields can be atoms or strings.
 
   Fields that are not present in the schema (or `types` map) are ignored.
   If any of the values has invalid type, an error is raised.
 
   To load data from non-database sources, use `Ecto.embedded_load/3`.
 
   ## Examples
 
       iex> MyRepo.load(User, %{name: "Alice", age: 25})
       %User{name: "Alice", age: 25}
 
       iex> MyRepo.load(User, [name: "Alice", age: 25])
       %User{name: "Alice", age: 25}
 
   `data` can also take form of `{fields, values}`:
 
       iex> MyRepo.load(User, {[:name, :age], ["Alice", 25]})
       %User{name: "Alice", age: 25, ...}
 
   The first argument can also be a `types` map:
 
       iex> types = %{name: :string, age: :integer}
       iex> MyRepo.load(types, %{name: "Alice", age: 25})
       %{name: "Alice", age: 25}
 
   This function is especially useful when parsing raw query results:
 
       iex> result = Ecto.Adapters.SQL.query!(MyRepo, "SELECT * FROM users", [])
       iex> Enum.map(result.rows, &MyRepo.load(User, {result.columns, &1}))
       [%User{...}, ...]
 
   """
   @doc group: "Schema API"
   @callback load(
               schema_or_map :: module | map(),
               data :: map() | Keyword.t() | {list, list}
             ) :: Ecto.Schema.t() | map()
 
   @doc """
   Returns the atom name or pid of the current repository.
 
   See `c:put_dynamic_repo/1` for more information.
   """
   @doc group: "Runtime API"
   @callback get_dynamic_repo() :: atom() | pid()
 
   @doc """
   Sets the dynamic repository to be used in further interactions.
 
   Sometimes you may want a single Ecto repository to talk to
   many different database instances. By default, when you call
   `MyApp.Repo.start_link/1`, it will start a repository with
   name `MyApp.Repo`. But if you want to start multiple repositories,
   you can give each of them a different name:
 
       MyApp.Repo.start_link(name: :tenant_foo, hostname: "foo.example.com")
       MyApp.Repo.start_link(name: :tenant_bar, hostname: "bar.example.com")
 
   You can also start repositories without names by explicitly
   setting the name to nil:
 
       MyApp.Repo.start_link(name: nil, hostname: "temp.example.com")
 
   However, once the repository is started, you can't directly interact with
   it, since all operations in `MyApp.Repo` are sent by default to the repository
   named `MyApp.Repo`. You can change the default repo at compile time with:
 
       use Ecto.Repo, default_dynamic_repo: :name_of_repo
 
   Or you can change it anytime at runtime by calling `put_dynamic_repo/1`:
 
       MyApp.Repo.put_dynamic_repo(:tenant_foo)
 
   From this moment on, all future queries done by the current process will
   run on `:tenant_foo`.
   """
   @doc group: "Runtime API"
   @callback put_dynamic_repo(name_or_pid :: atom() | pid()) :: atom() | pid()
 
   ## Ecto.Adapter.Queryable
 
   @optional_callbacks get: 3, get!: 3, get_by: 3, get_by!: 3, reload: 2, reload!: 2, aggregate: 3,
                       aggregate: 4, exists?: 2, one: 2, one!: 2, preload: 3, all: 2, stream: 2,
                       update_all: 3, delete_all: 2
 
   @doc """
   Fetches a single struct from the data store where the primary key matches the
   given id.
 
   Returns `nil` if no result was found. If the struct in the queryable
   has no or more than one primary key, it will raise an argument error.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       MyRepo.get(Post, 42)
 
       MyRepo.get(Post, 42, prefix: "public")
 
   """
   @doc group: "Query API"
   @callback get(queryable :: Ecto.Queryable.t(), id :: term, opts :: Keyword.t()) ::
               Ecto.Schema.t() | term | nil
 
   @doc """
   Similar to `c:get/3` but raises `Ecto.NoResultsError` if no record was found.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       MyRepo.get!(Post, 42)
 
       MyRepo.get!(Post, 42, prefix: "public")
 
   """
   @doc group: "Query API"
   @callback get!(queryable :: Ecto.Queryable.t(), id :: term, opts :: Keyword.t()) ::
               Ecto.Schema.t() | term
 
   @doc """
   Fetches a single result from the query.
 
   Returns `nil` if no result was found. Raises if more than one entry.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       MyRepo.get_by(Post, title: "My post")
 
       MyRepo.get_by(Post, [title: "My post"], prefix: "public")
 
   """
   @doc group: "Query API"
   @callback get_by(
               queryable :: Ecto.Queryable.t(),
               clauses :: Keyword.t() | map,
               opts :: Keyword.t()
             ) :: Ecto.Schema.t()  | term | nil
 
   @doc """
   Similar to `c:get_by/3` but raises `Ecto.NoResultsError` if no record was found.
 
   Raises if more than one entry.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       MyRepo.get_by!(Post, title: "My post")
 
       MyRepo.get_by!(Post, [title: "My post"], prefix: "public")
 
   """
   @doc group: "Query API"
   @callback get_by!(
               queryable :: Ecto.Queryable.t(),
               clauses :: Keyword.t() | map,
               opts :: Keyword.t()
             ) :: Ecto.Schema.t() | term
 
   @doc """
   Reloads a given schema or schema list from the database.
 
   When using with lists, it is expected that all of the structs in the list belong
   to the same schema. Ordering is guaranteed to be kept. Results not found in
   the database will be returned as `nil`.
 
   ## Example
 
       MyRepo.reload(post)
       %Post{}
 
       MyRepo.reload([post1, post2])
       [%Post{}, %Post{}]
 
       MyRepo.reload([deleted_post, post1])
       [nil, %Post{}]
   """
   @doc group: "Schema API"
   @callback reload(
               struct_or_structs :: Ecto.Schema.t() | [Ecto.Schema.t()],
               opts :: Keyword.t()
             ) :: Ecto.Schema.t() | [Ecto.Schema.t() | nil] | nil
 
   @doc """
   Similar to `c:reload/2`, but raises when something is not found.
 
   When using with lists, ordering is guaranteed to be kept.
 
   ## Example
 
       MyRepo.reload!(post)
       %Post{}
 
       MyRepo.reload!([post1, post2])
       [%Post{}, %Post{}]
   """
   @doc group: "Schema API"
   @callback reload!(struct_or_structs, opts :: Keyword.t()) :: struct_or_structs
             when struct_or_structs: Ecto.Schema.t() | [Ecto.Schema.t()]
 
   @doc """
   Calculate the given `aggregate`.
 
   If the query has a limit, offset, distinct or combination set, it will be
   automatically wrapped in a subquery in order to return the
   proper result.
 
   Any preload or select in the query will be ignored in favor of
   the column being aggregated.
 
   The aggregation will fail if any `group_by` field is set.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Examples
 
       # Returns the number of blog posts
       Repo.aggregate(Post, :count)
 
       # Returns the number of blog posts in the "private" schema path
       # (in Postgres) or database (in MySQL)
       Repo.aggregate(Post, :count, prefix: "private")
 
   """
   @doc group: "Query API"
   @callback aggregate(
               queryable :: Ecto.Queryable.t(),
               aggregate :: :count,
               opts :: Keyword.t()
             ) :: term | nil
 
   @doc """
   Calculate the given `aggregate` over the given `field`.
 
   See `c:aggregate/3` for general considerations and options.
 
   ## Examples
 
       # Returns the number of visits per blog post
       Repo.aggregate(Post, :count, :visits)
 
       # Returns the number of visits per blog post in the "private" schema path
       # (in Postgres) or database (in MySQL)
       Repo.aggregate(Post, :count, :visits, prefix: "private")
 
       # Returns the average number of visits for the top 10
       query = from Post, limit: 10
       Repo.aggregate(query, :avg, :visits)
   """
   @doc group: "Query API"
   @callback aggregate(
               queryable :: Ecto.Queryable.t(),
               aggregate :: :avg | :count | :max | :min | :sum,
               field :: atom,
               opts :: Keyword.t()
             ) :: term | nil
 
   @doc """
   Checks if there exists an entry that matches the given query.
 
   Returns a boolean.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Examples
 
       # checks if any posts exist
       Repo.exists?(Post)
 
       # checks if any posts exist in the "private" schema path (in Postgres) or
       # database (in MySQL)
       Repo.exists?(Post, schema: "private")
 
       # checks if any post with a like count greater than 10 exists
       query = from p in Post, where: p.like_count > 10
       Repo.exists?(query)
   """
   @doc group: "Query API"
   @callback exists?(queryable :: Ecto.Queryable.t(), opts :: Keyword.t()) :: boolean()
 
   @doc """
   Fetches a single result from the query.
 
   Returns `nil` if no result was found. Raises if more than one entry.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Examples
 
       Repo.one(from p in Post, join: c in assoc(p, :comments), where: p.id == ^post_id)
 
       query = from p in Post, join: c in assoc(p, :comments), where: p.id == ^post_id
       Repo.one(query, prefix: "private")
   """
   @doc group: "Query API"
   @callback one(queryable :: Ecto.Queryable.t(), opts :: Keyword.t()) ::
               Ecto.Schema.t() | term | nil
 
   @doc """
   Similar to `c:one/2` but raises `Ecto.NoResultsError` if no record was found.
 
   Raises if more than one entry.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
   """
   @doc group: "Query API"
   @callback one!(queryable :: Ecto.Queryable.t(), opts :: Keyword.t()) ::
               Ecto.Schema.t() | term
 
   @doc """
   Preloads all associations on the given struct or structs.
 
   This is similar to `Ecto.Query.preload/3` except it allows
   you to preload structs after they have been fetched from the
   database.
 
   In case the association was already loaded, preload won't attempt
   to reload it.
 
   ## Options
 
     * `:force` - By default, Ecto won't preload associations that
       are already loaded. By setting this option to true, any existing
       association will be discarded and reloaded.
     * `:in_parallel` - If the preloads must be done in parallel. It can
       only be performed when we have more than one preload and the
       repository is not in a transaction. Defaults to `true`.
     * `:prefix` - the prefix to fetch preloads from. By default, queries
       will use the same prefix as the first struct in the given collection.
       This option allows the prefix to be changed.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Examples
 
       # Use a single atom to preload an association
       posts = Repo.preload posts, :comments
 
       # Use a list of atoms to preload multiple associations
       posts = Repo.preload posts, [:comments, :authors]
 
       # Use a keyword list to preload nested associations as well
       posts = Repo.preload posts, [comments: [:replies, :likes], authors: []]
 
       # You can mix atoms and keywords, but the atoms must come first
       posts = Repo.preload posts, [:authors, comments: [:likes, replies: [:reactions]]]
 
       # Use a keyword list to customize how associations are queried
       posts = Repo.preload posts, [comments: from(c in Comment, order_by: c.published_at)]
 
       # Use a two-element tuple for a custom query and nested association definition
       query = from c in Comment, order_by: c.published_at
       posts = Repo.preload posts, [comments: {query, [:replies, :likes]}]
 
   The query given to preload may also preload its own associations.
   """
   @doc group: "Schema API"
   @callback preload(structs_or_struct_or_nil, preloads :: term, opts :: Keyword.t()) ::
               structs_or_struct_or_nil
             when structs_or_struct_or_nil: [Ecto.Schema.t()] | Ecto.Schema.t() | nil
 
   @doc """
   A user customizable callback invoked for query-based operations.
 
   This callback can be used to further modify the query and options
   before it is transformed and sent to the database.
 
   This callback is invoked for all query APIs, including the `stream`
   functions. It is also invoked for `insert_all` if a source query is
   given. It is not invoked for any of the other schema functions.
 
   ## Examples
 
   Let's say you want to filter out records that were "soft-deleted"
   (have `deleted_at` column set) from all operations unless an admin
   is running the query; you can define the callback like this:
 
       @impl true
       def prepare_query(_operation, query, opts) do
         if opts[:admin] do
           {query, opts}
         else
           query = from(x in query, where: is_nil(x.deleted_at))
           {query, opts}
         end
       end
 
   And then execute the query:
 
       Repo.all(query)              # only non-deleted records are returned
       Repo.all(query, admin: true) # all records are returned
 
   The callback will be invoked for all queries, including queries
   made from associations and preloads. It is not invoked for each
   individual join inside a query.
   """
   @doc group: "User callbacks"
   @callback prepare_query(operation, query :: Ecto.Query.t(), opts :: Keyword.t()) ::
               {Ecto.Query.t(), Keyword.t()}
             when operation: :all | :update_all | :delete_all | :stream | :insert_all
 
   @doc """
   A user customizable callback invoked to retrieve default options
   for operations.
 
   This can be used to provide default values per operation that
   have higher precedence than the values given on configuration
   or when starting the repository. It can also be used to set
   query specific options, such as `:prefix`.
 
   This callback is invoked as the entry point for all repository
   operations. For example, if you are executing a query with preloads,
   this callback will be invoked once at the beginning, but the
   options returned here will be passed to all following operations.
   """
   @doc group: "User callbacks"
   @callback default_options(operation) :: Keyword.t()
             when operation: :all | :insert_all | :update_all | :delete_all | :stream |
                               :transaction | :insert | :update | :delete | :insert_or_update
 
   @doc """
   Fetches all entries from the data store matching the given query.
 
   May raise `Ecto.QueryError` if query validation fails.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       # Fetch all post titles
       query = from p in Post,
            select: p.title
       MyRepo.all(query)
   """
   @doc group: "Query API"
   @callback all(queryable :: Ecto.Queryable.t(), opts :: Keyword.t()) :: [Ecto.Schema.t() | term]
 
   @doc """
   Returns a lazy enumerable that emits all entries from the data store
   matching the given query.
 
   SQL adapters, such as Postgres and MySQL, can only enumerate a stream
   inside a transaction.
 
   May raise `Ecto.QueryError` if query validation fails.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This will be applied to all `from`
       and `join`s in the query that did not have a prefix previously given
       either via the `:prefix` option on `join`/`from` or via `@schema_prefix`
       in the schema. For more information see the "Query Prefix" section of the
       `Ecto.Query` documentation.
 
     * `:max_rows` - The number of rows to load from the database as we stream.
       It is supported at least by Postgres and MySQL and defaults to 500.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       # Fetch all post titles
       query = from p in Post,
            select: p.title
       stream = MyRepo.stream(query)
       MyRepo.transaction(fn ->
         Enum.to_list(stream)
       end)
   """
   @doc group: "Query API"
   @callback stream(queryable :: Ecto.Queryable.t(), opts :: Keyword.t()) :: Enum.t()
 
   @doc """
   Updates all entries matching the given query with the given values.
 
   It returns a tuple containing the number of entries and any returned
   result as second element. The second element is `nil` by default
   unless a `select` is supplied in the update query. Note, however,
   not all databases support returning data from UPDATEs.
 
   Keep in mind this `update_all` will not update autogenerated
   fields like the `updated_at` columns.
 
   See `Ecto.Query.update/3` for update operations that can be
   performed on fields.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set in the schema.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for remaining options.
 
   ## Examples
 
       MyRepo.update_all(Post, set: [title: "New title"])
 
       MyRepo.update_all(Post, inc: [visits: 1])
 
       from(p in Post, where: p.id < 10, select: p.visits)
       |> MyRepo.update_all(set: [title: "New title"])
 
       from(p in Post, where: p.id < 10, update: [set: [title: "New title"]])
       |> MyRepo.update_all([])
 
       from(p in Post, where: p.id < 10, update: [set: [title: ^new_title]])
       |> MyRepo.update_all([])
 
       from(p in Post, where: p.id < 10, update: [set: [title: fragment("upper(?)", ^new_title)]])
       |> MyRepo.update_all([])
 
       from(p in Post, where: p.id < 10, update: [set: [visits: p.visits * 1000]])
       |> MyRepo.update_all([])
 
   """
   @doc group: "Query API"
   @callback update_all(
               queryable :: Ecto.Queryable.t(),
               updates :: Keyword.t(),
               opts :: Keyword.t()
             ) :: {non_neg_integer, nil | [term]}
 
   @doc """
   Deletes all entries matching the given query.
 
   It returns a tuple containing the number of entries and any returned
   result as second element. The second element is `nil` by default
   unless a `select` is supplied in the delete query. Note, however,
   not all databases support returning data from DELETEs.
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set in the schema.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for remaining options.
 
   ## Examples
 
       MyRepo.delete_all(Post)
 
       from(p in Post, where: p.id < 10) |> MyRepo.delete_all
   """
   @doc group: "Query API"
   @callback delete_all(queryable :: Ecto.Queryable.t(), opts :: Keyword.t()) ::
               {non_neg_integer, nil | [term]}
 
   ## Ecto.Adapter.Schema
 
   @optional_callbacks insert_all: 3, insert: 2, insert!: 2, update: 2, update!: 2,
                       delete: 2, delete!: 2, insert_or_update: 2, insert_or_update!: 2,
                       prepare_query: 3
 
   @doc """
   Inserts all entries into the repository.
 
   It expects a schema module (`MyApp.User`) or a source (`"users"`) or
   both (`{"users", MyApp.User}`) as the first argument. The second
   argument is a list of entries to be inserted, either as keyword
   lists or as maps. The keys of the entries are the field names as
   atoms and the value should be the respective value for the field
   type or, optionally, an `Ecto.Query` that returns a single entry
   with a single value.
 
   It returns a tuple containing the number of entries
   and any returned result as second element. If the database
   does not support RETURNING in INSERT statements or no
   return result was selected, the second element will be `nil`.
 
   When a schema module is given, the entries given will be properly dumped
   before being sent to the database. If the schema primary key has type
   `:id` or `:binary_id`, it will be handled either at the adapter
   or the storage layer. However any other primary key type or autogenerated
   value, like `Ecto.UUID` and timestamps, won't be autogenerated when
   using `c:insert_all/3`. You must set those fields explicitly. This is by
   design as this function aims to be a more direct way to insert data into
   the database without the conveniences of `c:insert/2`. This is also
   consistent with `c:update_all/3` that does not handle auto generated
   values as well.
 
   It is also not possible to use `insert_all` to insert across multiple
   tables, therefore associations are not supported.
 
   If a source is given, without a schema module, the given fields are passed
   as is to the adapter.
 
   ## Options
 
     * `:returning` - selects which fields to return. When `true`,
       returns all fields in the given schema. May be a list of
       fields, where a struct is still returned but only with the
       given fields. Or `false`, where nothing is returned (the default).
       This option is not supported by all databases.
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set in the schema.
 
     * `:on_conflict` - It may be one of `:raise` (the default), `:nothing`,
       `:replace_all`, `{:replace_all_except, fields}`, `{:replace, fields}`,
       a keyword list of update instructions or an `Ecto.Query`
       query for updates. See the "Upserts" section for more information.
 
     * `:conflict_target` - A list of column names to verify for conflicts.
       It is expected those columns to have unique indexes on them that may conflict.
       If none is specified, the conflict target is left up to the database.
       It may also be `{:unsafe_fragment, binary_fragment}` to pass any
       expression to the database without any sanitization, this is useful
       for partial index or index with expressions, such as
       `{:unsafe_fragment, "(coalesce(firstname, ""), coalesce(lastname, "")) WHERE middlename IS NULL"}` for
       `ON CONFLICT (coalesce(firstname, ""), coalesce(lastname, "")) WHERE middlename IS NULL` SQL query.
 
     * `:placeholders` - A map with placeholders. This feature is not supported
       by all databases. See the "Placeholders" section for more information.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for remaining options.
 
   ## Source query
 
   A query can be given instead of a list with entries. This query needs to select
   into a map containing only keys that are available as writeable columns in the
   schema.
 
   ## Examples
 
       MyRepo.insert_all(Post, [[title: "My first post"], [title: "My second post"]])
 
       MyRepo.insert_all(Post, [%{title: "My first post"}, %{title: "My second post"}])
 
       query = from p in Post,
         join: c in assoc(p, :comments),
         select: %{
           author_id: p.author_id,
           posts: count(p.id, :distinct),
           interactions: sum(p.likes) + count(c.id)
         },
         group_by: p.author_id
       MyRepo.insert_all(AuthorStats, query)
 
   ## Upserts
 
   `c:insert_all/3` provides upserts (update or inserts) via the `:on_conflict`
   option. The `:on_conflict` option supports the following values:
 
     * `:raise` - raises if there is a conflicting primary key or unique index
 
     * `:nothing` - ignores the error in case of conflicts
 
     * `:replace_all` - replace **all** values on the existing row with the values
       in the schema/changeset, including fields not explicitly set in the changeset,
       such as IDs and autogenerated timestamps (`inserted_at` and `updated_at`).
       Do not use this option if you have auto-incrementing primary keys, as they
       will also be replaced. You most likely want to use `{:replace_all_except, [:id]}`
       or `{:replace, fields}` explicitly instead. This option requires a schema
 
     * `{:replace_all_except, fields}` - same as above except the given fields
       are not replaced. This option requires a schema
 
     * `{:replace, fields}` - replace only specific columns. This option requires
       `:conflict_target`
 
     * a keyword list of update instructions - such as the one given to
       `c:update_all/3`, for example: `[set: [title: "new title"]]`
 
     * an `Ecto.Query` that will act as an `UPDATE` statement, such as the
       one given to `c:update_all/3`
 
   Upserts map to "ON CONFLICT" on databases like Postgres and "ON DUPLICATE KEY"
   on databases such as MySQL.
 
   ## Return values
 
   By default, both Postgres and MySQL will return the number of entries
   inserted on `c:insert_all/3`. However, when the `:on_conflict` option
   is specified, Postgres and MySQL will return different results.
 
   Postgres will only count a row if it was affected and will
   return 0 if no new entry was added.
 
   MySQL will return, at a minimum, the number of entries attempted. For example,
   if `:on_conflict` is set to `:nothing`, MySQL will return
   the number of entries attempted to be inserted, even when no entry
   was added.
 
   Also note that if `:on_conflict` is a query, MySQL will return
   the number of attempted entries plus the number of entries modified
   by the UPDATE query.
 
   ## Placeholders
 
   Passing in a map for the `:placeholders` allows you to send less
   data over the wire when you have many entries with the same value
   for a field. To use a placeholder, replace its value in each of your
   entries with `{:placeholder, key}`,  where `key` is the key you
   are using in the `:placeholders` option map. For example:
 
       placeholders = %{blob: large_blob_of_text(...)}
 
       entries = [
         %{title: "v1", body: {:placeholder, :blob}},
         %{title: "v2", body: {:placeholder, :blob}}
       ]
 
       Repo.insert_all(Post, entries, placeholders: placeholders)
 
   Keep in mind that:
 
     * placeholders cannot be nested in other values. For example, you
       cannot put a placeholder inside an array. Instead, the whole
       array has to be the placeholder
 
     * a placeholder key can only be used with columns of the same type
 
     * placeholders require a database that supports index parameters,
       so they are not currently compatible with MySQL
 
   """
   @doc group: "Schema API"
   @callback insert_all(
               schema_or_source :: binary | {binary, module} | module,
               entries_or_query :: [%{atom => value} | Keyword.t(value)] | Ecto.Query.t,
               opts :: Keyword.t()
             ) :: {non_neg_integer, nil | [term]} when value: term | Ecto.Query.t()
 
   @doc """
   Inserts a struct defined via `Ecto.Schema` or a changeset.
 
   In case a struct is given, the struct is converted into a changeset
   with all non-nil fields as part of the changeset.
 
   In case a changeset is given, the changes in the changeset are
   merged with the struct fields, and all of them are sent to the
   database. If more than one database operation is required, they're
   automatically wrapped in a transaction.
 
   It returns `{:ok, struct}` if the struct has been successfully
   inserted or `{:error, changeset}` if there was a validation
   or a known constraint error.
 
   ## Options
 
     * `:returning` - selects which fields to return. It accepts a list
       of fields to be returned from the database. When `true`, returns
       all fields. When `false`, no extra fields are returned. It will
       always include all fields in `read_after_writes` as well as any
       autogenerated id. Not all databases support this option and it
       may not be available during upserts. See the "Upserts" section
       for more information.
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set any schemas. Also, the
       `@schema_prefix` for the parent record will override all default
       `@schema_prefix`s set in any child schemas for associations.
 
     * `:on_conflict` - It may be one of `:raise` (the default), `:nothing`,
       `:replace_all`, `{:replace_all_except, fields}`, `{:replace, fields}`,
       a keyword list of update instructions or an `Ecto.Query` query for updates.
       See the "Upserts" section for more information.
 
     * `:conflict_target` - A list of column names to verify for conflicts.
       It is expected those columns to have unique indexes on them that may conflict.
       If none is specified, the conflict target is left up to the database.
       It may also be `{:unsafe_fragment, binary_fragment}` to pass any
       expression to the database without any sanitization, this is useful
       for partial index or index with expressions, such as
       `{:unsafe_fragment, "(coalesce(firstname, ""), coalesce(lastname, "")) WHERE middlename IS NULL"}` for
       `ON CONFLICT (coalesce(firstname, ""), coalesce(lastname, "")) WHERE middlename IS NULL` SQL query.
 
     * `:stale_error_field` - The field where stale errors will be added in
       the returning changeset. This option can be used to avoid raising
       `Ecto.StaleEntryError`.
 
     * `:stale_error_message` - The message to add to the configured
       `:stale_error_field` when stale errors happen, defaults to "is stale".
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Examples
 
   A typical example is calling `MyRepo.insert/1` with a struct
   and acting on the return value:
 
       case MyRepo.insert %Post{title: "Ecto is great"} do
         {:ok, struct}       -> # Inserted with success
         {:error, changeset} -> # Something went wrong
       end
 
   ## Upserts
 
   `c:insert/2` provides upserts (update or inserts) via the `:on_conflict`
   option. The `:on_conflict` option supports the following values:
 
     * `:raise` - raises if there is a conflicting primary key or unique index
 
     * `:nothing` - ignores the error in case of conflicts
 
     * `:replace_all` - replace **all** values on the existing row with the values
       in the schema/changeset, including fields not explicitly set in the changeset,
       such as IDs and autogenerated timestamps (`inserted_at` and `updated_at`).
       Do not use this option if you have auto-incrementing primary keys, as they
       will also be replaced. You most likely want to use `{:replace_all_except, [:id]}`
       or `{:replace, fields}` explicitly instead. This option requires a schema
 
     * `{:replace_all_except, fields}` - same as above except the given fields are
       not replaced. This option requires a schema
 
     * `{:replace, fields}` - replace only specific columns. This option requires
       `:conflict_target`
 
     * a keyword list of update instructions - such as the one given to
       `c:update_all/3`, for example: `[set: [title: "new title"]]`
 
     * an `Ecto.Query` that will act as an `UPDATE` statement, such as the
       one given to `c:update_all/3`. Similarly to `c:update_all/3`, auto
       generated values, such as timestamps are not automatically updated.
       If the struct cannot be found, `Ecto.StaleEntryError` will be raised.
 
   Upserts map to "ON CONFLICT" on databases like Postgres and "ON DUPLICATE KEY"
   on databases such as MySQL.
 
   As an example, imagine `:title` is marked as a unique column in
   the database:
 
       {:ok, inserted} = MyRepo.insert(%Post{title: "this is unique"})
 
   Now we can insert with the same title but do nothing on conflicts:
 
       {:ok, ignored} = MyRepo.insert(%Post{title: "this is unique"}, on_conflict: :nothing)
 
   Because we used `on_conflict: :nothing`, instead of getting an error,
   we got `{:ok, struct}`. However the returned struct does not reflect
   the data in the database. If the primary key is auto-generated by the
   database, the primary key in the `ignored` record will be nil if there
   was no insertion. For example, if you use the default primary key
   (which has name `:id` and a type of `:id`), then `ignored.id` above
   will be nil if there was no insertion.
 
   If your id is generated by your application (typically the case for
   `:binary_id`) or if you pass another value for `:on_conflict`, detecting
   if an insert or update happened is slightly more complex, as the database
   does not actually inform us what happened. Let's insert a post with the
   same title but use a query to update the body column in case of conflicts:
 
       # In Postgres (it requires the conflict target for updates):
       on_conflict = [set: [body: "updated"]]
       {:ok, updated} = MyRepo.insert(%Post{title: "this is unique"},
                                      on_conflict: on_conflict, conflict_target: :title)
 
       # In MySQL (conflict target is not supported):
       on_conflict = [set: [title: "updated"]]
       {:ok, updated} = MyRepo.insert(%Post{id: inserted.id, title: "updated"},
                                      on_conflict: on_conflict)
 
   In the examples above, even though it returned `:ok`, we do not know
   if we inserted new data or if we updated only the `:on_conflict` fields.
   In case an update happened, the data in the struct most likely does
   not match the data in the database. For example, autogenerated fields
   such as `inserted_at` will point to now rather than the time the
   struct was actually inserted.
 
   If you need to guarantee the data in the returned struct mirrors the
   database, you have three options:
 
     * Use `on_conflict: :replace_all`, although that will replace all
       fields in the database with the ones in the struct/changeset,
       including autogenerated fields such as `inserted_at` and `updated_at`:
 
           MyRepo.insert(%Post{title: "this is unique"},
                         on_conflict: :replace_all, conflict_target: :title)
 
     * Specify `read_after_writes: true` in your schema for choosing
       fields that are read from the database after every operation.
       Or pass `returning: true` to `insert` to read all fields back:
 
           MyRepo.insert(%Post{title: "this is unique"}, returning: true,
                         on_conflict: on_conflict, conflict_target: :title)
 
     * Alternatively, read the data again from the database in a separate
       query. This option requires the primary key to be generated by the
       database:
 
           {:ok, updated} = MyRepo.insert(%Post{title: "this is unique"}, on_conflict: on_conflict)
           Repo.get(Post, updated.id)
 
   Because of the inability to know if the struct is up to date or not,
   inserting a struct with associations and using the `:on_conflict` option
   at the same time is not recommended, as Ecto will be unable to actually
   track the proper status of the association.
   """
   @doc group: "Schema API"
   @callback insert(
               struct_or_changeset :: Ecto.Schema.t() | Ecto.Changeset.t(),
               opts :: Keyword.t()
             ) :: {:ok, Ecto.Schema.t()} | {:error, Ecto.Changeset.t()}
 
   @doc """
   Updates a changeset using its primary key.
 
   A changeset is required as it is the only mechanism for
   tracking dirty changes. Only the fields present in the `changes` part
   of the changeset are sent to the database. Any other, in-memory
   changes done to the schema are ignored. If more than one database
   operation is required, they're automatically wrapped in a transaction.
 
   If the struct has no primary key, `Ecto.NoPrimaryKeyFieldError`
   will be raised.
 
   If the struct cannot be found, `Ecto.StaleEntryError` will be raised.
 
   It returns `{:ok, struct}` if the struct has been successfully
   updated or `{:error, changeset}` if there was a validation
   or a known constraint error.
 
   ## Options
 
     * `:returning` - selects which fields to return. It accepts a list
       of fields to be returned from the database. When `true`, returns
       all fields. When `false`, no extra fields are returned. It will
       always include all fields in `read_after_writes`. Not all
       databases support this option.
 
     * `:force` - By default, if there are no changes in the changeset,
       `c:update/2` is a no-op. By setting this option to true, update
       callbacks will always be executed, even if there are no changes
       (including timestamps).
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set any schemas. Also, the
       `@schema_prefix` for the parent record will override all default
       `@schema_prefix`s set in any child schemas for associations.
 
     * `:stale_error_field` - The field where stale errors will be added in
       the returning changeset. This option can be used to avoid raising
       `Ecto.StaleEntryError`.
 
     * `:stale_error_message` - The message to add to the configured
       `:stale_error_field` when stale errors happen, defaults to "is stale".
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       post = MyRepo.get!(Post, 42)
       post = Ecto.Changeset.change post, title: "New title"
       case MyRepo.update post do
         {:ok, struct}       -> # Updated with success
         {:error, changeset} -> # Something went wrong
       end
   """
   @doc group: "Schema API"
   @callback update(changeset :: Ecto.Changeset.t(), opts :: Keyword.t()) ::
               {:ok, Ecto.Schema.t()} | {:error, Ecto.Changeset.t()}
 
   @doc """
   Inserts or updates a changeset depending on whether the struct is persisted
   or not.
 
   The distinction whether to insert or update will be made on the
   `Ecto.Schema.Metadata` field `:state`. The `:state` is automatically set by
   Ecto when loading or building a schema.
 
   Please note that for this to work, you will have to load existing structs from
   the database. So even if the struct exists, this won't work:
 
       struct = %Post{id: "existing_id", ...}
       MyRepo.insert_or_update changeset
       # => {:error, changeset} # id already exists
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set any schemas. Also, the
       `@schema_prefix` for the parent record will override all default
       `@schema_prefix`s set in any child schemas for associations.
     * `:stale_error_field` - The field where stale errors will be added in
       the returning changeset. This option can be used to avoid raising
       `Ecto.StaleEntryError`. Only applies to updates.
     * `:stale_error_message` - The message to add to the configured
       `:stale_error_field` when stale errors happen, defaults to "is stale".
       Only applies to updates.
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       result =
         case MyRepo.get(Post, id) do
           nil  -> %Post{id: id} # Post not found, we build one
           post -> post          # Post exists, let's use it
         end
         |> Post.changeset(changes)
         |> MyRepo.insert_or_update
 
       case result do
         {:ok, struct}       -> # Inserted or updated with success
         {:error, changeset} -> # Something went wrong
       end
   """
   @doc group: "Schema API"
   @callback insert_or_update(changeset :: Ecto.Changeset.t(), opts :: Keyword.t()) ::
               {:ok, Ecto.Schema.t()} | {:error, Ecto.Changeset.t()}
 
   @doc """
   Deletes a struct using its primary key.
 
   If the struct has no primary key, `Ecto.NoPrimaryKeyFieldError`
   will be raised. If the struct has been removed prior to the call,
   `Ecto.StaleEntryError` will be raised. If more than one database
   operation is required, they're automatically wrapped in a transaction.
 
   It returns `{:ok, struct}` if the struct has been successfully
   deleted or `{:error, changeset}` if there was a validation
   or a known constraint error. By default, constraint errors will
   raise the `Ecto.ConstraintError` exception, unless a changeset is
   given as the first argument with the relevant constraints declared
   in it (see `Ecto.Changeset`).
 
   ## Options
 
     * `:prefix` - The prefix to run the query on (such as the schema path
       in Postgres or the database in MySQL). This overrides the prefix set
       in the query and any `@schema_prefix` set in the schema.
 
     * `:stale_error_field` - The field where stale errors will be added in
       the returning changeset. This option can be used to avoid raising
       `Ecto.StaleEntryError`.
 
     * `:stale_error_message` - The message to add to the configured
       `:stale_error_field` when stale errors happen, defaults to "is stale".
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
 
   ## Example
 
       post = MyRepo.get!(Post, 42)
       case MyRepo.delete post do
         {:ok, struct}       -> # Deleted with success
         {:error, changeset} -> # Something went wrong
       end
 
   """
   @doc group: "Schema API"
   @callback delete(
               struct_or_changeset :: Ecto.Schema.t() | Ecto.Changeset.t(),
               opts :: Keyword.t()
             ) :: {:ok, Ecto.Schema.t()} | {:error, Ecto.Changeset.t()}
 
   @doc """
   Same as `c:insert/2` but returns the struct or raises if the changeset is invalid.
   """
   @doc group: "Schema API"
   @callback insert!(
               struct_or_changeset :: Ecto.Schema.t() | Ecto.Changeset.t(),
               opts :: Keyword.t()
             ) :: Ecto.Schema.t()
 
   @doc """
   Same as `c:update/2` but returns the struct or raises if the changeset is invalid.
   """
   @doc group: "Schema API"
   @callback update!(changeset :: Ecto.Changeset.t(), opts :: Keyword.t()) ::
               Ecto.Schema.t()
 
   @doc """
   Same as `c:insert_or_update/2` but returns the struct or raises if the changeset
   is invalid.
   """
   @doc group: "Schema API"
   @callback insert_or_update!(changeset :: Ecto.Changeset.t(), opts :: Keyword.t()) ::
               Ecto.Schema.t()
 
   @doc """
   Same as `c:delete/2` but returns the struct or raises if the changeset is invalid.
   """
   @doc group: "Schema API"
   @callback delete!(
               struct_or_changeset :: Ecto.Schema.t() | Ecto.Changeset.t(),
               opts :: Keyword.t()
             ) :: Ecto.Schema.t()
 
   ## Ecto.Adapter.Transaction
 
   @optional_callbacks transaction: 2, in_transaction?: 0, rollback: 1
 
   @doc """
   Runs the given function or `Ecto.Multi` inside a transaction.
 
   ## Use with function
 
   `c:transaction/2` can be called with both a function of arity
   zero or one. The arity zero function will just be executed as is:
 
       import Ecto.Changeset, only: [change: 2]
 
       MyRepo.transaction(fn ->
         MyRepo.update!(change(alice, balance: alice.balance - 10))
         MyRepo.update!(change(bob, balance: bob.balance + 10))
       end)
 
   While the arity one function will receive the repo of the transaction
   as its first argument:
 
       MyRepo.transaction(fn repo ->
         repo.insert!(%Post{})
       end)
 
   If an Elixir exception occurs the transaction will be rolled back
   and the exception will bubble up from the transaction function.
   If no exception occurs, the transaction is committed when the
   function returns. A transaction can be explicitly rolled back
   by calling `c:rollback/1`, this will immediately leave the function
   and return the value given to `rollback` as `{:error, value}`.
 
   A successful transaction returns the value returned by the function
   wrapped in a tuple as `{:ok, value}`.
 
   ### Nested transactions
 
   If `c:transaction/2` is called inside another transaction, the function
   is simply executed, without wrapping the new transaction call in any
   way. If there is an error in the inner transaction and the error is
   rescued, or the inner transaction is rolled back, the whole outer
   transaction is aborted, guaranteeing nothing will be committed.
 
   Below is an example of how rollbacks work with nested transactions:
 
       {:error, :rollback} =
         MyRepo.transaction(fn ->
           {:error, :posting_not_allowed} =
             MyRepo.transaction(fn ->
               # This function call causes the following to happen:
               #
               #   * the transaction is rolled back in the database,
               #   * code execution is stopped within the current function,
               #   * and the value, passed to `rollback/1` is returned from
               #     `MyRepo.transaction/1` as the second element in the error
               #     tuple.
               #
               MyRepo.rollback(:posting_not_allowed)
 
               # `rollback/1` stops execution, so code here won't be run
             end)
 
           # The transaction here is now aborted and any further
           # operation will raise an exception.
         end)
 
   See the "Aborted transactions" section for more examples of aborted
   transactions and how to handle them.
 
   In practice, managing nested transactions can become complex quickly.
   For this reason, Ecto provides `Ecto.Multi` for composing transactions.
 
   ## Use with Ecto.Multi
 
   `c:transaction/2` also accepts the `Ecto.Multi` struct as first argument.
   `Ecto.Multi` allows you to compose transactions operations, step by step,
   and manage what happens in case of success or failure.
 
   When an `Ecto.Multi` is given to this function, a transaction will be started,
   all operations applied and in case of success committed returning `{:ok, changes}`:
 
       # With Ecto.Multi
       Ecto.Multi.new()
       |> Ecto.Multi.insert(:post, %Post{})
       |> MyRepo.transaction
 
   In case of any errors the transaction will be rolled back and
   `{:error, failed_operation, failed_value, changes_so_far}` will be returned.
 
   Explore the `Ecto.Multi` documentation to learn more and find detailed examples.
 
   ## Aborted transactions
 
   When an operation inside a transaction fails, the transaction is aborted in the database. 
   For instance, if you attempt an insert that violates a unique constraint, the insert fails 
   and the transaction is aborted. In such cases, any further operation inside the transaction 
   will raise exceptions.
 
   Take the following transaction as an example:
 
       Repo.transaction(fn repo ->
         case repo.insert(changeset) do
           {:ok, post} ->
             repo.insert(%Status{value: "success"})
 
           {:error, changeset} ->
             repo.insert(%Status{value: "failure"})
         end
       end)
 
   If the changeset is valid, but the insert operation fails due to a database constraint,
   the subsequent `repo.insert(%Failure{})` operation will raise an exception because the
   database has already aborted the transaction and thus making the operation invalid.
   In Postgres, the exception would look like this:
   
       ** (Postgrex.Error) ERROR 25P02 (in_failed_sql_transaction) current transaction is aborted, commands ignored until end of transaction block
       
   If the changeset is invalid before it reaches the database due to a validation error, 
   no statement is sent to the database, an `:error` tuple is returned, and `repo.insert(%Failure{})` 
   operation will execute as usual. 
 
   We have two options to deal with such scenarios:
   
   If don't want to change the semantics of your code,  you can also use the savepoints 
   feature by passing the `:mode` option like this: `repo.insert(changeset, mode: :savepoint)`. 
   In case of an exception, the transaction will rollback to the savepoint and prevent 
   the transaction from failing.
 
   Another alternative is to handle this operation outside of the transaction. 
   For example, you can choose to perform an explicit `repo.rollback` call in the 
   `{:error, changeset}` clause and then perform the `repo.insert(%Failure{})` outside 
   of the transaction. You might also consider using `Ecto.Multi`, as they automatically 
   rollback whenever an operation fails.
 
   ## Working with processes
 
   The transaction is per process. A separate process started inside a
   transaction won't be part of the same transaction and will use a separate
   connection altogether.
 
   When using the the `Ecto.Adapters.SQL.Sandbox` in tests, while it may be
   possible to share the connection between processes, the parent process
   will typically hold the connection until the transaction completes. This
   may lead to a deadlock if the child process attempts to use the same connection.
   See the docs for
   [`Ecto.Adapters.SQL.Sandbox`](https://hexdocs.pm/ecto_sql/Ecto.Adapters.SQL.Sandbox.html)
   for more information.
 
   ## Options
 
   See the ["Shared options"](#module-shared-options) section at the module
   documentation for more options.
   """
   @doc group: "Transaction API"
   @callback transaction(fun_or_multi :: fun | Ecto.Multi.t(), opts :: Keyword.t()) ::
               {:ok, any}
               | {:error, any}
               | {:error, Ecto.Multi.name(), any, %{Ecto.Multi.name() => any}}
 
   @doc """
   Returns true if the current process is inside a transaction.
 
   If you are using the `Ecto.Adapters.SQL.Sandbox` in tests, note that even
   though each test is inside a transaction, `in_transaction?/0` will only
   return true inside transactions explicitly created with `transaction/2`. This
   is done so the test environment mimics dev and prod.
 
   ## Examples
 
       MyRepo.in_transaction?
       #=> false
 
       MyRepo.transaction(fn ->
         MyRepo.in_transaction? #=> true
       end)
 
   """
   @doc group: "Transaction API"
   @callback in_transaction?() :: boolean
 
   @doc """
   Rolls back the current transaction.
 
   The transaction will return the value given as `{:error, value}`.
 
   Note that calling `rollback` causes the code in the transaction to stop executing.
   """
   @doc group: "Transaction API"
   @callback rollback(value :: any) :: no_return
 end