How to Submit Both JSON and Files in a FastAPI POST Request?

How to Add Both File and JSON Body in a FastAPI POST Request?

In FastAPI, you cannot send both JSON data and files in a single request if you declare the body as JSON. Instead, you need to use multipart/form-data encoding. Here are a few methods to achieve this:

Method 1: Using File and Form

# Assuming you have a DataConfiguration model for the JSON data
from fastapi import FastAPI, File, UploadFile
from pydantic import BaseModel

app = FastAPI()

class DataConfiguration(BaseModel):
    textColumnNames: list[str]
    idColumn: str

@app.post("/data")
async def data(dataConfiguration: DataConfiguration,
               csvFile: UploadFile = File(...)):
    pass  # read requested id and text columns from csvFile

Method 2: Using Pydantic Models and Dependencies

from fastapi import FastAPI, Form, File, UploadFile, Depends, Request
from pydantic import BaseModel
from typing import List, Optional, Dict
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates

app = FastAPI()
templates = Jinja2Templates(directory="templates")

class Base(BaseModel):
    name: str
    point: Optional[float] = None
    is_accepted: Optional[bool] = False

def validate_json_body(body: str = Form(...)):
    try:
        return Base.model_validate_json(body)
    except ValidationError as e:
        raise HTTPException(
            detail=jsonable_encoder(e.errors()),
            status_code=422,
        )

@app.post("/submit")
async def submit(base: Base = Depends(validate_json_body),
                  files: List[UploadFile] = File(...)):
    return {
        "JSON Payload": base,
        "Filenames": [file.filename for file in files],
    }

@app.get("/", response_class=HTMLResponse)
async def main(request: Request):
    return templates.TemplateResponse("index.html", {"request": request})

Method 3: Passing JSON as String in Body Parameter

from fastapi import FastAPI, Form, UploadFile, File
from pydantic import BaseModel

class Base(BaseModel):
    name: str
    point: float
    is_accepted: bool

app = FastAPI()

@app.post("/submit")
async def submit(data: Base = Form(...), files: List[UploadFile] = File(...)):
    return {
        "JSON Payload": data,
        "Filenames": [file.filename for file in files],
    }

Method 4: Using a Custom Class to Validate JSON

from fastapi import FastAPI, File, UploadFile, Request
from pydantic import BaseModel, model_validator
from typing import Optional, List
from fastapi.responses import HTMLResponse
from fastapi.templating import Jinja2Templates
import json

app = FastAPI()
templates = Jinja2Templates(directory="templates")

class Base(BaseModel):
    name: str
    point: Optional[float] = None
    is_accepted: Optional[bool] = False

    @model_validator(mode='before')
    @classmethod
    def validate_to_json(cls, value):
        if isinstance(value, str):
            return cls(**json.loads(value))
        return value

@app.post("/submit")
async def submit(data: Base = Body(...), files: List[UploadFile] = File(...)):
    return {
        "JSON Payload": data,
        "Filenames": [file.filename for file in files],
    }

@app.get("/", response_class=HTMLResponse)
async def main(request: Request):
    return templates.TemplateResponse("index.html", context={"request": request})

Note: In Method 1, you can use the File and Form classes together because Form is a subclass of Body. However, if you use Body(...) instead of Form(...) in Method 1, it will not work because FastAPI will expect the JSON data to be in the request body, not as form data.

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