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Dependencies

FastAPI Batteries comes with some handful dependencies that are common in most FastAPI projects.

File Validator

This dependency uses python-magic to accurately determine the file type of the uploaded file.

You can use this validator to:

  • Validate the file type (via mime type)
  • Validate File Size
from typing import Annotated

from fastapi import Depends, FastAPI, UploadFile

from fastapi_batteries.fastapi.deps import FileValidator
from fastapi_batteries.utils.size import mb_to_bytes

app = FastAPI()


img_validator_upto_1mb = FileValidator(
    max_size_bytes=mb_to_bytes(1),
    allowed_mime_types=["image/jpeg", "image/png", "image/svg+xml", "image/webp"],
)

pdf_validator_upto_5mb = FileValidator(max_size_bytes=mb_to_bytes(5), allowed_mime_types=["application/pdf"])


@app.post("/upload/")
async def upload_file(file: Annotated[UploadFile, Depends(img_validator_upto_1mb)]): ...

fastapi_batteries__file_validator_mime_type_err

Pagination Query Params

FastAPI allows using Pydantic model as query parameter model.

Thanks to that you can have reusable pagination query parameters. This is minimal but faster and when you pair it with our CRUD helper it becomes more powerful.

from typing import Annotated

from fastapi import FastAPI, Query

from fastapi_batteries.pydantic.schemas import PaginationOffsetLimit, PaginationPageSize

app = FastAPI()


@app.get("/items/")
async def get_items_page_size_pagination(pagination: Annotated[PaginationPageSize, Query()]):
    return pagination


@app.get("/products/")
async def get_products_offset_limit_pagination(pagination: Annotated[PaginationOffsetLimit, Query()]):
    return pagination

fastapi_batteries__pagination_ss

Using with other query params

When you use Pydantic model schema along with other query params you'll get Pydantic model schema in request body which is wrong:

from typing import Annotated

from fastapi import FastAPI, Query

from fastapi_batteries.pydantic.schemas import PaginationPageSize

app = FastAPI()


@app.get("/items/")
async def get_items_page_size_pagination(
    pagination: Annotated[PaginationPageSize, Query()],
    q: str = "",
):
    return {"q": q, "pagination": pagination}

fastapi_pydantic_model_n_query_param_issue

This is limitation (or bug) from FastAPI. There's already open issue and related discussions for this. However, we've nice workaround for this.

We just have to replace Query() with Depends() and it'll work as expected:

- pagination: Annotated[PaginationPageSize, Query()],
+ pagination: Annotated[PaginationPageSize, Depends()],

from typing import Annotated

from fastapi import Depends, FastAPI

from fastapi_batteries.pydantic.schemas import PaginationPageSize

app = FastAPI()


@app.get("/items/")
async def get_items_page_size_pagination(
    pagination: Annotated[PaginationPageSize, Depends()],
    q: str = "",
):
    return {"q": q, "pagination": pagination}

fastapi_batteries__