Form Models¶
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You can use Pydantic models to declare form fields in FastAPI.
Info
To use forms, first install python-multipart
.
Make sure you create a virtual environment, activate it, and then install it, for example:
$ pip install python-multipart
Note
This is supported since FastAPI version 0.113.0
. 🤓
Pydantic Models for Forms¶
You just need to declare a Pydantic model with the fields you want to receive as form fields, and then declare the parameter as Form
:
from typing import Annotated
from fastapi import FastAPI, Form
from pydantic import BaseModel
app = FastAPI()
class FormData(BaseModel):
username: str
password: str
@app.post("/login/")
async def login(data: Annotated[FormData, Form()]):
return data
from fastapi import FastAPI, Form
from pydantic import BaseModel
from typing_extensions import Annotated
app = FastAPI()
class FormData(BaseModel):
username: str
password: str
@app.post("/login/")
async def login(data: Annotated[FormData, Form()]):
return data
Tip
Prefer to use the Annotated
version if possible.
from fastapi import FastAPI, Form
from pydantic import BaseModel
app = FastAPI()
class FormData(BaseModel):
username: str
password: str
@app.post("/login/")
async def login(data: FormData = Form()):
return data
FastAPI will extract the data for each field from the form data in the request and give you the Pydantic model you defined.
Check the Docs¶
You can verify it in the docs UI at /docs
:
Forbid Extra Form Fields¶
In some special use cases (probably not very common), you might want to restrict the form fields to only those declared in the Pydantic model. And forbid any extra fields.
Note
This is supported since FastAPI version 0.114.0
. 🤓
You can use Pydantic's model configuration to forbid
any extra
fields:
from typing import Annotated
from fastapi import FastAPI, Form
from pydantic import BaseModel
app = FastAPI()
class FormData(BaseModel):
username: str
password: str
model_config = {"extra": "forbid"}
@app.post("/login/")
async def login(data: Annotated[FormData, Form()]):
return data
from fastapi import FastAPI, Form
from pydantic import BaseModel
from typing_extensions import Annotated
app = FastAPI()
class FormData(BaseModel):
username: str
password: str
model_config = {"extra": "forbid"}
@app.post("/login/")
async def login(data: Annotated[FormData, Form()]):
return data
Tip
Prefer to use the Annotated
version if possible.
from fastapi import FastAPI, Form
from pydantic import BaseModel
app = FastAPI()
class FormData(BaseModel):
username: str
password: str
model_config = {"extra": "forbid"}
@app.post("/login/")
async def login(data: FormData = Form()):
return data
If a client tries to send some extra data, they will receive an error response.
For example, if the client tries to send the form fields:
username
:Rick
password
:Portal Gun
extra
:Mr. Poopybutthole
They will receive an error response telling them that the field extra
is not allowed:
{
"detail": [
{
"type": "extra_forbidden",
"loc": ["body", "extra"],
"msg": "Extra inputs are not permitted",
"input": "Mr. Poopybutthole"
}
]
}
Summary¶
You can use Pydantic models to declare form fields in FastAPI. 😎