FastAPI, Pydantic, and OpenAPI with recursive models

README.md

Exploring limitations of FastAPI with recursive models

References

• pydantic/pydantic#3251
• tiangolo/fastapi#836

app.py

## Models

from __future__ import annotations
from dataclasses import dataclass
import pydantic
from typing import Optional


# @dataclass
# class Node:
#     left: Optional[Node] = None
#     right: Optional[Node] = None
#
#
# class Tree(pydantic.BaseModel): # This raises: Exception has occurred: RecursionError
#     root_node: Node
#
#
# PydanticNode = pydantic.dataclasses.dataclass(Node) # This raises: Exception has occurred: RecursionError


class Node(pydantic.BaseModel):
    left: Optional[Node] = None
    right: Optional[Node] = None


class Tree(pydantic.BaseModel):
    root_node: Node


## App

from fastapi import FastAPI


app = FastAPI()


@app.post("/")
def index(tree: Tree):
    return tree


if __name__ == "__main__":
    import uvicorn

    uvicorn.run(app)