RedisOM Pydantic objects cause POST request errors with FastAPI

[aleexharris]

If using a Redis-OM Pydantic object as the input for a FastAPI route with a version greater than 0.112, you get the error shown below. NOTE: You don't even need to be trying to access the underlying RedisDB for this issue to occur, it is native to the Redis-OM wrapper around Pydantic.

To recreate for yourself:

# pyproject.toml

dependencies = [
    "fastapi[standard]==0.113",
    "redis-om>=0.3.3",
]

# main.py

from fastapi import FastAPI
from redis_om import JsonModel

class Name(JsonModel):
    greet: str

app = FastAPI()

@app.post("/greet")
async def greet(name: Name):
    # NOTE: You don't even need to interact with name to cause an error
    return {"message": "Hello World"}

The error:

pydantic.errors.PydanticSchemaGenerationError: Unable to generate pydantic-core schema for <class 'redis_om.model.model.ExpressionProxy'>. Set arbitrary_types_allowed=True in the model_config to ignore this error or implement __get_pydantic_core_schema__ on your type to fully support it.
If you got this error by calling handler() within __get_pydantic_core_schema__ then you likely need to call handler.generate_schema(<some type>) since we do not call __get_pydantic_core_schema__ on <some type> otherwise to avoid infinite recursion.
For further information visit https://errors.pydantic.dev/2.10/u/schema-for-unknown-type

[AdolfoVillalobos]

Hi! Im experiencing the same issue. Did you find a solution?

[aleexharris]

Hi! Im experiencing the same issue. Did you find a solution?

The only solution I have found is to cap the version of my FastAPI import to 0.112 and then work everything around that.

# pyproject.toml
dependencies = [
    "fastapi[standard]==0.112",
    "redis-om>=0.3.3",
]

I believe this means that under-the-hood, you end up using Pydantic version 2.8.2 via RedisOM.