# Fixtures

Dependency-aware database seeding with context-based loading strategies.

## Overview

The `fixtures` module lets you define named fixtures with dependencies between them, then load them into the database in the correct order. Fixtures can be scoped to contexts (e.g. base data, testing data) so that only the relevant ones are loaded for each environment.

## Defining fixtures

```python
from fastapi_toolsets.fixtures import FixtureRegistry, Context

fixtures = FixtureRegistry()


@fixtures.register
def roles():
    return [
        Role(id=1, name="admin"),
        Role(id=2, name="user"),
    ]


@fixtures.register(depends_on=["roles"], contexts=[Context.TESTING])
def test_users():
    return [
        User(id=1, username="alice", role_id=1),
        User(id=2, username="bob", role_id=2),
    ]
```

Dependencies declared via `depends_on` are resolved topologically — `roles` will always be loaded before `test_users`.

## Loading fixtures

By context with [`load_fixtures_by_context`](../reference/fixtures.md#fastapi_toolsets.fixtures.utils.load_fixtures_by_context):

```python
from fastapi_toolsets.fixtures import load_fixtures_by_context

async with db_context() as session:
    await load_fixtures_by_context(session, fixtures, Context.TESTING)
```

Directly by name with [`load_fixtures`](../reference/fixtures.md#fastapi_toolsets.fixtures.utils.load_fixtures):

```python
from fastapi_toolsets.fixtures import load_fixtures

async with db_context() as session:
    await load_fixtures(session, fixtures, "roles", "test_users")
```

Both functions return a `dict[str, list[...]]` mapping each fixture name to the list of loaded instances.

## Contexts

[`Context`](../reference/fixtures.md#fastapi_toolsets.fixtures.enum.Context) is an enum with predefined values:

| Context | Description |
|---------|-------------|
| `Context.BASE` | Core data required in all environments |
| `Context.TESTING` | Data only loaded during tests |
| `Context.DEVELOPMENT` | Data only loaded in development |
| `Context.PRODUCTION` | Data only loaded in production |

A fixture with no `contexts` defined takes `Context.BASE` by default.

`Context.BASE` fixtures are always included alongside whatever context you load or list — there's no way to load a non-base context in isolation:

```python
# also loads any Context.BASE fixtures, even though only TESTING is requested
await load_fixtures_by_context(session, fixtures, Context.TESTING)
```

### Custom contexts

Plain strings and any `Enum` subclass are accepted wherever a `Context` enum is expected.

```python
from enum import Enum


class AppContext(str, Enum):
    STAGING = "staging"
    DEMO = "demo"


@fixtures.register(contexts=[AppContext.STAGING])
def staging_data():
    return [Config(key="feature_x", enabled=True)]


# loads staging_data plus any Context.BASE fixtures
await load_fixtures_by_context(session, fixtures, AppContext.STAGING)
```

### Default context for a registry

Pass `contexts` to `FixtureRegistry` to set a default for all fixtures registered in it:

```python
testing_registry = FixtureRegistry(contexts=[Context.TESTING])


@testing_registry.register  # implicitly contexts=[Context.TESTING]
def test_orders():
    return [Order(id=1, total=99)]
```

### Same fixture name, multiple context variants

The same fixture name may be registered under different (non-overlapping) context sets. When multiple contexts are loaded together, all matching variants are merged:

```python
@fixtures.register(contexts=[Context.BASE])
def users():
    return [User(id=1, username="admin")]


@fixtures.register(contexts=[Context.TESTING])
def users():
    return [User(id=2, username="tester")]


# loads both admin and tester (Context.BASE is included automatically)
await load_fixtures_by_context(session, fixtures, Context.TESTING)
```

Registering two variants with overlapping context sets raises `ValueError`.

## Load strategies

[`LoadStrategy`](../reference/fixtures.md#fastapi_toolsets.fixtures.enum.LoadStrategy) controls how the fixture loader handles rows that already exist:

| Strategy | Description |
|----------|-------------|
| `LoadStrategy.INSERT` | Insert only, fail on duplicates |
| `LoadStrategy.MERGE` | Insert or update on conflict (default) |
| `LoadStrategy.SKIP_EXISTING` | Skip rows that already exist |

```python
await load_fixtures_by_context(
    session, fixtures, Context.BASE, strategy=LoadStrategy.SKIP_EXISTING
)
```

## Merging registries

Split fixture definitions across modules and merge them:

```python
from myapp.fixtures.dev import dev_fixtures
from myapp.fixtures.prod import prod_fixtures

fixtures = FixtureRegistry()
fixtures.include_registry(registry=dev_fixtures)
fixtures.include_registry(registry=prod_fixtures)
```

Fixtures with the same name are allowed as long as their context sets do not overlap. Conflicting contexts raise `ValueError`.

## Looking up fixture instances

[`FixtureRegistry.obj`](../reference/fixtures.md#fastapi_toolsets.fixtures.registry.FixtureRegistry.obj) retrieves a specific instance from a registered fixture by attribute value, looked up by name on the registry — useful when building cross-fixture `depends_on` relationships:

```python
@fixtures.register(depends_on=["roles"])
def users():
    admin_role = fixtures.obj("roles", "name", "admin")
    return [User(id=1, username="alice", role_id=admin_role.id)]
```

Looking the fixture up by name (instead of importing the `roles` function directly) means fixture modules never need to import each other, which avoids circular imports in larger projects split across multiple files — the same reason `depends_on` takes fixture names rather than the functions themselves. The registry passed in must be the one that actually contains the fixture by load time; with a single shared registry this is automatic, but if you merge registries with `include_registry`, call `obj`/`field` on the merged registry.

[`FixtureRegistry.field`](../reference/fixtures.md#fastapi_toolsets.fixtures.registry.FixtureRegistry.field) is shorthand for pulling a single attribute (`id` by default):

```python
@fixtures.register(depends_on=["roles"])
def users():
    return [
        User(id=1, username="alice", role_id=fixtures.field("roles", "name", "admin"))
    ]
```

Both raise `StopIteration` if no matching instance is found, and `KeyError` if the fixture name isn't registered.

## Pytest integration

Use [`register_fixtures`](../reference/pytest.md#fastapi_toolsets.pytest.plugin.register_fixtures) to expose each fixture in your registry as an injectable pytest fixture named `fixture_{name}` by default:

```python
# conftest.py
import pytest
from fastapi_toolsets.pytest import create_db_session, register_fixtures
from app.fixtures import registry
from app.models import Base

DATABASE_URL = "postgresql+asyncpg://user:pass@localhost/test_db"


@pytest.fixture
async def db_session():
    async with create_db_session(
        database_url=DATABASE_URL, base=Base, cleanup=True
    ) as session:
        yield session


register_fixtures(registry=registry, namespace=globals())
```

```python
# test_users.py
async def test_user_can_login(fixture_users: list[User], fixture_roles: list[Role]): ...
```

The load order is resolved automatically from the `depends_on` declarations in your registry. Each generated fixture receives `db_session` as a dependency and returns the list of loaded model instances.

## CLI integration

Fixtures can be triggered from the CLI. See the [CLI module](cli.md) for setup instructions.

---

[:material-api: API Reference](../reference/fixtures.md)