Dependencies in path operation decorators
In some cases you don't really need the return value of a dependency inside your path operation function.
Or the dependency doesn't return a value.
But you still need it to be executed/solved.
For those cases, instead of declaring a path operation function parameter with Depends, you can add a list of dependencies to the path operation decorator.
Add dependencies to the path operation decorator
Section titled “Add dependencies to the path operation decorator”The path operation decorator receives an optional argument dependencies.
It should be a list of Depends():
from typing import Annotated
from fastapi import Depends, FastAPI, Header, HTTPException
app = FastAPI()
async def verify_token(x_token: Annotated[str, Header()]):
if x_token != "fake-super-secret-token":
raise HTTPException(status_code=400, detail="X-Token header invalid")
async def verify_key(x_key: Annotated[str, Header()]):
if x_key != "fake-super-secret-key":
raise HTTPException(status_code=400, detail="X-Key header invalid")
return x_key
@app.get("/items/", dependencies=[Depends(verify_token), Depends(verify_key)])
async def read_items():
return [{"item": "Foo"}, {"item": "Bar"}]These dependencies will be executed/solved the same way as normal dependencies. But their value (if they return any) won't be passed to your path operation function.
Dependencies errors and return values
Section titled “Dependencies errors and return values”You can use the same dependency functions you use normally.
Dependency requirements
Section titled “Dependency requirements”They can declare request requirements (like headers) or other sub-dependencies:
from typing import Annotated
from fastapi import Depends, FastAPI, Header, HTTPException
app = FastAPI()
async def verify_token(x_token: Annotated[str, Header()]):
if x_token != "fake-super-secret-token":
raise HTTPException(status_code=400, detail="X-Token header invalid")
async def verify_key(x_key: Annotated[str, Header()]):
if x_key != "fake-super-secret-key":
raise HTTPException(status_code=400, detail="X-Key header invalid")
return x_key
@app.get("/items/", dependencies=[Depends(verify_token), Depends(verify_key)])
async def read_items():
return [{"item": "Foo"}, {"item": "Bar"}]Raise exceptions
Section titled “Raise exceptions”These dependencies can raise exceptions, the same as normal dependencies:
from typing import Annotated
from fastapi import Depends, FastAPI, Header, HTTPException
app = FastAPI()
async def verify_token(x_token: Annotated[str, Header()]):
if x_token != "fake-super-secret-token":
raise HTTPException(status_code=400, detail="X-Token header invalid")
async def verify_key(x_key: Annotated[str, Header()]):
if x_key != "fake-super-secret-key":
raise HTTPException(status_code=400, detail="X-Key header invalid")
return x_key
@app.get("/items/", dependencies=[Depends(verify_token), Depends(verify_key)])
async def read_items():
return [{"item": "Foo"}, {"item": "Bar"}]Return values
Section titled “Return values”And they can return values or not, the values won't be used.
So, you can reuse a normal dependency (that returns a value) you already use somewhere else, and even though the value won't be used, the dependency will be executed:
from typing import Annotated
from fastapi import Depends, FastAPI, Header, HTTPException
app = FastAPI()
async def verify_token(x_token: Annotated[str, Header()]):
if x_token != "fake-super-secret-token":
raise HTTPException(status_code=400, detail="X-Token header invalid")
async def verify_key(x_key: Annotated[str, Header()]):
if x_key != "fake-super-secret-key":
raise HTTPException(status_code=400, detail="X-Key header invalid")
return x_key
@app.get("/items/", dependencies=[Depends(verify_token), Depends(verify_key)])
async def read_items():
return [{"item": "Foo"}, {"item": "Bar"}]Dependencies for a group of path operations
Section titled “Dependencies for a group of path operations”Later, when reading about how to structure bigger applications (Bigger Applications - Multiple Files), possibly with multiple files, you will learn how to declare a single dependencies parameter for a group of path operations.
Global Dependencies
Section titled “Global Dependencies”Next we will see how to add dependencies to the whole FastAPI application, so that they apply to each path operation.