# Dependencies - `Depends()` and `Security()`

## `Depends()`

Dependencies are handled mainly with the special function `Depends()` that takes a callable.

Here is the reference for it and its parameters.

You can import it directly from `fastapi`:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

# Abhängigkeiten – `Depends()` und `Security()`

## `Depends()`

Abhängigkeiten werden hauptsächlich mit der speziellen Funktion `Depends()` behandelt, die ein Callable entgegennimmt.

Hier finden Sie deren Referenz und Parameter.

Sie können sie direkt von `fastapi` importieren:

```python
from fastapi import Depends
```

::: fastapi.Depends

## `Security()`

    return user


async def get_current_active_user(current_user: User = Depends(get_current_user)):
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user


@app.post("/token")
async def login_for_access_token(
    form_data: OAuth2PasswordRequestForm = Depends(),
) -> Token:

    ```

**FastAPI** 🤙 `CommonQueryParams` 🎓. 👉 ✍ "👐" 👈 🎓 & 👐 🔜 🚶‍♀️ 🔢 `commons` 👆 🔢.

## 🆎 ✍ 🆚 `Depends`

👀 ❔ 👥 ✍ `CommonQueryParams` 🕐 🔛 📟:

```Python
commons: CommonQueryParams = Depends(CommonQueryParams)
```

🏁 `CommonQueryParams`,:

```Python
... = Depends(CommonQueryParams)
```

...⚫️❔ **FastAPI** 🔜 🤙 ⚙️ 💭 ⚫️❔ 🔗.

from fastapi import Depends, FastAPI

app = FastAPI()


async def common_parameters(
    q: Union[str, None] = None, skip: int = 0, limit: int = 100
):
    return {"q": q, "skip": skip, "limit": limit}


@app.get("/items/")
async def read_items(commons: dict = Depends(common_parameters)):
    return commons


@app.get("/users/")
async def read_users(commons: dict = Depends(common_parameters)):

@app.get("/async")
async def get_async(state: str = Depends(asyncgen_state)):
    return state


@app.get("/sync")
async def get_sync(state: str = Depends(generator_state)):
    return state


@app.get("/async_raise")
async def get_async_raise(state: str = Depends(asyncgen_state_try)):
    assert state == "asyncgen raise started"
    raise AsyncDependencyError()

@app.get("/callable-dependency")
async def get_callable_dependency(value: str = Depends(callable_dependency)):
    return value


@app.get("/callable-gen-dependency")
async def get_callable_gen_dependency(value: str = Depends(callable_gen_dependency)):
    return value


@app.get("/async-callable-dependency")
async def get_async_callable_dependency(
    value: str = Depends(async_callable_dependency),
):
    return value

from typing import Union

from fastapi import Cookie, Depends, FastAPI
from typing_extensions import Annotated

app = FastAPI()


def query_extractor(q: Union[str, None] = None):
    return q


def query_or_cookie_extractor(
    q: Annotated[str, Depends(query_extractor)],
    last_query: Annotated[Union[str, None], Cookie()] = None,
):
    if not q:
        return last_query
    return q


@app.get("/items/")

from fastapi import Depends
from typing_extensions import Annotated


async def dependency_a():
    dep_a = generate_dep_a()
    try:
        yield dep_a
    finally:
        dep_a.close()


async def dependency_b(dep_a: Annotated[DepA, Depends(dependency_a)]):
    dep_b = generate_dep_b()
    try:
        yield dep_b
    finally:
        dep_b.close(dep_a)

    db_user = crud.get_user_by_email(db, email=user.email)
    if db_user:
        raise HTTPException(status_code=400, detail="Email already registered")
    return crud.create_user(db=db, user=user)


@app.get("/users/", response_model=list[schemas.User])
def read_users(skip: int = 0, limit: int = 100, db: Session = Depends(get_db)):
    users = crud.get_users(db, skip=skip, limit=limit)
    return users