Ecto v3.1.1 Ecto.Adapter behaviour View Source

Specifies the minimal API required from adapters.

Link to this section Summary

Types

The metadata returned by the adapter init/1.

t()

Functions

Returns the adapter metadata from the init/1 callback.

Callbacks

The callback invoked in case the adapter needs to inject code.

Checks out a connection for the duration of the given function.

Returns the dumpers for a given type.

Ensure all applications necessary to run the adapter are started.

Initializes the adapter supervision tree by returning the children and adapter metadata.

Returns the loaders for a given type.

Link to this section Types

Link to this type

adapter_meta() View Source
adapter_meta() :: map()

The metadata returned by the adapter init/1.

It must be a map and Ecto itself will always inject two keys into the meta:

  • the :cache key, which as ETS table that can be used as a cache (if available)
  • the :pid key, which is the PID returned by the child spec returned in init/1

Link to this section Functions

Link to this function

lookup_meta(repo_name_or_pid) View Source

Returns the adapter metadata from the init/1 callback.

It expects a name or a PID representing a repo.

Link to this section Callbacks

Link to this macrocallback

__before_compile__(env) View Source
__before_compile__(term(), env :: Macro.Env.t()) :: Macro.t()

The callback invoked in case the adapter needs to inject code.

Link to this callback

checkout(adapter_meta, config, function) View Source
checkout(adapter_meta(), config :: Keyword.t(), (() -> result)) :: result
when result: var

Checks out a connection for the duration of the given function.

In case the adapter provides a pool, this guarantees all of the code inside the given fun runs against the same connection, which might improve performance by for instance allowing multiple related calls to the datastore to share cache information:

Repo.checkout(fn ->
  for _ <- 100 do
    Repo.insert!(%Post{})
  end
end)

If the adapter does not provide a pool, just calling the passed function and returning its result are enough.

If the adapter provides a pool, it is supposed to "check out" one of the pool connections for the duration of the function call. Which connection is checked out is not passed to the calling function, so it should be done using a stateful method like using the current process' dictionary, process tracking, or some kind of other lookup method. Make sure that this stored connection is then used in the other callbacks implementations, such as Ecto.Adapter.Queryable and Ecto.Adapter.Schema.

Link to this callback

dumpers(primitive_type, ecto_type) View Source
dumpers(primitive_type :: Ecto.Type.primitive(), ecto_type :: Ecto.Type.t()) ::
  [(term() -> {:ok, term()} | :error) | Ecto.Type.t()]

Returns the dumpers for a given type.

It receives the primitive type and the Ecto type (which may be primitive as well). It returns a list of dumpers with the given type usually at the beginning.

This allows developers to properly translate values coming from the Ecto into adapter ones. For example, if the database does not support booleans but instead returns 0 and 1 for them, you could add:

def dumpers(:boolean, type), do: [type, &bool_encode/1]
def dumpers(_primitive, type), do: [type]

defp bool_encode(false), do: {:ok, 0}
defp bool_encode(true), do: {:ok, 1}

All adapters are required to implement a clause for :binary_id types, since they are adapter specific. If your adapter does not provide binary ids, you may simply use Ecto.UUID:

def dumpers(:binary_id, type), do: [type, Ecto.UUID]
def dumpers(_primitive, type), do: [type]
Link to this callback

ensure_all_started(config, type) View Source
ensure_all_started(config :: Keyword.t(), type :: :application.restart_type()) ::
  {:ok, [atom()]} | {:error, atom()}

Ensure all applications necessary to run the adapter are started.

Initializes the adapter supervision tree by returning the children and adapter metadata.

Link to this callback

loaders(primitive_type, ecto_type) View Source
loaders(primitive_type :: Ecto.Type.primitive(), ecto_type :: Ecto.Type.t()) ::
  [(term() -> {:ok, term()} | :error) | Ecto.Type.t()]

Returns the loaders for a given type.

It receives the primitive type and the Ecto type (which may be primitive as well). It returns a list of loaders with the given type usually at the end.

This allows developers to properly translate values coming from the adapters into Ecto ones. For example, if the database does not support booleans but instead returns 0 and 1 for them, you could add:

def loaders(:boolean, type), do: [&bool_decode/1, type]
def loaders(_primitive, type), do: [type]

defp bool_decode(0), do: {:ok, false}
defp bool_decode(1), do: {:ok, true}

All adapters are required to implement a clause for :binary_id types, since they are adapter specific. If your adapter does not provide binary ids, you may simply use Ecto.UUID:

def loaders(:binary_id, type), do: [Ecto.UUID, type]
def loaders(_primitive, type), do: [type]