How do I accept on a single route objects with array\single items using pydantic/fastapi?

Question

Say I have:

from pydantic import BaseModel
from typing import Optional, List

class Create(BaseModel):
    code: List[str] = []
    args: List[str] = []

Wrapped into something like

@router.post('/new', status_code=201)
async def create_project(data: Create):
    pass

So that code and/or args is an array or single value for the requestor?

Such that request to single rout could contain any of this:

{code: "code", args: "arg"}
{code: ["code"], args: "arg"}
{code: ["code"], args: ["arg"]}
{code: "code", args: ["arg"]}

And always call handler with real type that uses lists?

Answer 1

Pydantic models accept Union for the field definition, e.g.:

from typing import List, Union

class Create(BaseModel):
    code: Union[str, List[str]] = []
    args: Union[str, List[str]] = []

In this case, both code and args will accept either a str or a list/array of strs.

Both code and args will default to an empty list.

The rest of the code stays the same, e.g.:

from fastapi import FastAPI, status

app = FastAPI()

@app.post("/create", status_code=status.HTTP_201_CREATED)
async def create_project(data: Create):
    return data

Calling the endpoint with single item:

$ curl -i -X 'POST' 'http://127.0.0.1:8000/create' \
    -H 'accept: application/json' \
    -H 'Content-Type: application/json' \
    -d '{"code": "code", "args": "arg"}'

HTTP/1.1 201 Created
date: Sun, 29 Aug 2021 10:25:57 GMT
server: uvicorn
content-length: 28
content-type: application/json

{"code":"code","args":"arg"}

Calling the endpoint with multiple items:

$ curl -i -X 'POST' 'http://127.0.0.1:8000/create' \
    -H 'accept: application/json' \
    -H 'Content-Type: application/json' \
    -d '{"code": ["code"], "args": ["arg"]}'

HTTP/1.1 201 Created
date: Sun, 29 Aug 2021 10:27:03 GMT
server: uvicorn
content-length: 32
content-type: application/json

{"code":["code"],"args":["arg"]}