Custom Adapters

Blink uses an adapter pattern to support different database bulk insert implementations. While Blink ships with a PostgreSQL adapter (Blink.Adapter.Postgres), you can create custom adapters for other databases (e.g., MySQL).

The Adapter Behavior

All adapters must implement the Blink.Adapter behaviour, which requires a single callback:

@callback call(
  items :: Enumerable.t(),
  table_name :: binary() | atom(),
  repo :: Ecto.Repo.t(),
  opts :: Keyword.t()
) :: :ok

The call/4 function receives:

• items - An enumerable (list or stream) of maps to bulk insert into table
• table_name - Target table name
• repo - Ecto repository module
• opts - Adapter-specific options

Example:

defmodule MyApp.Adapters.MySQL do
  @behaviour Blink.Adapter

  @impl true
  def call(items, table_name, repo, opts \\ []) do
    # Your bulk insert implementation
    :ok
  end
end

The adapter should:

• Perform bulk insertion using database-specific commands
• Return :ok on success
• Raise an exception on failure

Using a Custom Adapter

Pass your adapter when calling run/3:

defmodule MyApp.Seeder do
  use Blink

  def call do
    new()
    |> with_table("users")
    |> run(MyApp.Repo, adapter: MyApp.Adapters.MySQL)
  end

  def table(_seeder, "users") do
    [
      %{id: 1, name: "Alice"},
      %{id: 2, name: "Bob"}
    ]
  end
end

Or use it directly with copy_to_table/4:

Blink.copy_to_table(items, "users", MyApp.Repo, adapter: MyApp.Adapters.MySQL)

Overriding the Run Function

For complete control over the insertion process, you can override the run/3 callback in your Blink module:

defmodule MyApp.Seeder do
  use Blink

  @impl true
  def run(%Seeder{} = seeder, repo, opts \\ []) do
    # Implement custom transaction logic, error handling, etc.
    # Tip: Blink.copy_to_table/4 is available for inserting data into individual tables
  end
end

This allows you to customize transaction behavior, error handling, or set a default adapter for all operations.

Reference

See Blink.Adapter.Postgres for a complete reference implementation using PostgreSQL's COPY FROM STDIN command.