17_ Form Data

17_ The form data

This section describes how to use Form Declare form data input parameters .

When we need to pass JSON When receiving field data , You can use forms Form.

To use forms , You need to install python-multipart

pip install python-multipart

Then you can go from fastapi Import Form Used ：

from fastapi import FastAPI, Form

---

1. Definition Form Parameters ：

create form （Form） Parameter mode and Body, Query equally ：

from fastapi import FastAPI, Form

app = FastAPI()


@app.post("/login/")
async def login(username: str = Form(), password: str = Form()):
    return {
    "username": username}

for example ,OAuth2 canonical “ Cryptoflow ” The mode specifies to send... Through form fields username and password. It requires that the field must be named username and password, And send... Through the form field , Out of commission JSON.

Use Form Can declare and Body( And Query, Path, Cookie) Same metadata and validation .

explain ： Form It is directly inherited from Body Class .

Be careful ：

Declare that the form body should explicitly use Form, otherwise ,FastAPI Parameters will be treated as query parameters or request body （JSON） Parameters .

---

2. About “ form field ”：

And JSON Different , HTML Forms （<form></form>） Data sent to the server is usually encoded in a special way .

FastAPI Make sure you read the data from the correct location , Instead of reading JSON.

Technical details ：

Form data “ Media type MIME” The code is generally application/x-www-form-urlencoded.

But the form containing the file is encoded as multipart/form-data . Document processing will be described later .

For details of codes and form fields, see MDN web Document POST Section .

Warning ：

Multiple... Can be declared in one path operation Form Parameters , But you can't declare to receive at the same time JSON Of Body Field . Because the code of the request body is application/x-www-form-urlencoded, No application/json.

This is not FastAPI The problem of , It is HTTP Provisions of the agreement .