Query parameters from pydantic model

Question

Is there a way to convert a pydantic model to query parameters in fastapi?

Some of my endpoints pass parameters via the body, but some others pass them directly in the query. All this endpoints share the same data model, for example:

class Model(BaseModel):
    x: str
    y: str

I would like to avoid duplicating my definition of this model in the definition of my "query-parameters endpoints", like for example test_query in this code:

class Model(BaseModel):
    x: str
    y: str

@app.post("/test-body")
def test_body(model: Model): pass

@app.post("/test-query-params")
def test_query(x: str, y: str): pass

What's the cleanest way of doing this?

Answer 1

The documentation gives a shortcut to avoid this kind of repetitions. In this case, it would give:

from fastapi import Depends

@app.post("/test-query-params")
def test_query(model: Model = Depends()): pass

This will allow you to request /test-query-params?x=1&y=2 and will also produce the correct OpenAPI description for this endpoint.

Similar solutions can be used for using Pydantic models as form-data descriptors.

Answer 2

This solution is very apt if your schema is "minimal".

But, when it comes to a complicated one like this, Set description for query parameter in swagger doc using Pydantic model, it is better to use a "custom dependency class"

from fastapi import Depends, FastAPI, Query

app = FastAPI()


class Model:
    def __init__(
            self,
            y: str,
            x: str = Query(
                default='default for X',
                title='Title for X',
                deprecated=True
            )

    ):
        self.x = x
        self.y = y


@app.post("/test-body")
def test_body(model: Model = Depends()):
    return model

If you are using this method, you will have more control over the OpenAPI doc.

Answer 3

Special case that isn't mentioned in the documentation for Query Parameters Lists, for example with:

/members/&member_ids=1&member_ids=2

The answer provided by @cglacet will unfortunately ignore the array for such a model:

class Model(BaseModel):
    member_ids: List[str]

You need to modify your model like so:

 class Model(BaseModel):
     member_ids: List[str] = Field(Query([]))

Answer from @fnep on GitHub here