# `Selecto.Extension`

Behavior contract for Selecto ecosystem extensions.

Extensions are loaded from domain definitions through the `:extensions` key.
A single extension can participate in multiple packages (`selecto`,
`selecto_components`, `selecto_updato`) by implementing the callbacks relevant
to that package.

## Domain Usage

    %{
      name: "Store",
      source: %{...},
      schemas: %{},
      joins: %{},
      extensions: [
        # From the :selecto_postgis package
        Selecto.Extensions.PostGIS,
        {MyApp.Selecto.Extensions.Timescale, hypertable: "events"}
      ]
    }

# `extension_opts`

```elixir
@type extension_opts() :: keyword()
```

# `extension_spec`

```elixir
@type extension_spec() :: module() | {module(), extension_opts()}
```

# `components_views`
*optional* 

```elixir
@callback components_views(selecto_or_domain :: map(), opts :: extension_opts()) :: [
  tuple()
]
```

Return additional `selecto_components` view tuples for this extension.

# `ecto_type_to_selecto_type`
*optional* 

```elixir
@callback ecto_type_to_selecto_type(ecto_type :: term(), opts :: extension_opts()) ::
  atom() | nil
```

Map Ecto schema field types to Selecto types during `Selecto.EctoAdapter`
introspection.

Return `nil` to indicate no mapping for the provided type.

# `merge_domain`
*optional* 

```elixir
@callback merge_domain(domain :: map(), opts :: extension_opts()) :: map()
```

Merge extension-provided defaults into a domain during `Selecto.configure/3`.

# `overlay_dsl_modules`
*optional* 

```elixir
@callback overlay_dsl_modules(opts :: extension_opts()) :: [module()]
```

Return DSL modules imported by `Selecto.Config.OverlayDSL` when this extension
is enabled in an overlay module.

# `overlay_fragment`
*optional* 

```elixir
@callback overlay_fragment(overlay_module :: module(), opts :: extension_opts()) :: map()
```

Build extension-owned overlay fragments during `@before_compile`.

# `overlay_setup`
*optional* 

```elixir
@callback overlay_setup(overlay_module :: module(), opts :: extension_opts()) :: :ok
```

Compile-time hook called from `Selecto.Config.OverlayDSL.__using__/1`.

Use this to register extension-specific module attributes for overlay DSL
directives.

# `updato_domain`
*optional* 

```elixir
@callback updato_domain(domain :: map(), opts :: extension_opts()) :: map()
```

Merge extension defaults into a domain used by `selecto_updato`.

---

*Consult [api-reference.md](api-reference.md) for complete listing*