> ## Documentation Index
> Fetch the complete documentation index at: https://fastql.vachagan.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom federation directives

> Use @external, @requires, @provides, @shareable, and @override in FastQL subgraphs.

Beyond `@key`, Apollo Federation v2 provides several directives that control field
ownership and sharing between subgraphs. All are available as helpers in
`fastql.federation`.

## `@external` — fields owned by another subgraph

Mark a field as externally owned with `external()`. External fields must be declared
for `@requires` to reference them but are not resolved by this subgraph.

```python theme={null}
from fastql import Field, Type
from fastql.federation import external, key, requires

@Type(directives=[key("id")])
class Product:
    id: str
    weight: float = Field(directives=[external()])

    @Field(directives=[requires("weight")])
    def shipping_estimate(self) -> float:
        return self.weight * 2.5
```

## `@requires` — computed fields that depend on external data

`requires(fields)` declares that a field computation needs external field values to
be fetched first. The router forwards those fields in the entity representation.

## `@provides` — eager-load related entity fields

`provides(fields)` tells the router that this subgraph can return the specified
fields of a related entity without an extra round-trip.

```python theme={null}
from fastql.federation import key, provides

@Type(directives=[key("id")])
class Order:
    id: str
    product: "Product" = Field(directives=[provides("name price")])
```

## `@shareable` — allow a field to be resolved by multiple subgraphs

By default, a non-entity object type's fields may only be resolved by one subgraph.
Apply `shareable()` to allow other subgraphs to also resolve those fields.

```python theme={null}
from fastql import Type
from fastql.federation import shareable

@Type(directives=[shareable()])
class Location:
    lat: float
    lon: float
```

## `@override` — migrate a field from another subgraph

`override(from_subgraph)` signals that this subgraph now owns a field that was
previously owned by another subgraph.

```python theme={null}
from fastql import Field, Type
from fastql.federation import key, override

@Type(directives=[key("id")])
class Product:
    id: str
    inventory: int = Field(directives=[override("inventory-service")])
```

## `@inaccessible` — hide from the public schema

`inaccessible()` excludes a type or field from the composed public API while still
making it available inside the federation for `@requires` / `@provides`.

## `@tag` — annotate for contract filtering

`tag(name)` attaches a named tag used with Apollo Contracts to produce filtered
schema variants.

***

**Previous:** [Entity resolution](/federation/entities) — `@key` and reference resolvers.