@computed_field not showing in OpenAPI Json

[Galarzaa90]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google "How to X in FastAPI" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from fastapi import FastAPI
import pydantic
import uvicorn

class StudentGrades(pydantic.BaseModel):
    english: int
    history: int
    geography: int

    @pydantic.computed_field()
    @property
    def grade(self) -> float:
        return (self.english + self.history + self.geography)/ 3
    

app = FastAPI()

@app.get("/")
def sample() -> StudentGrades:
    return StudentGrades(english=100, history=100, geography=70)

Description

When using model with a computed field, if I check the content of the response:

{
  "english": 100,
  "history": 100,
  "geography": 70,
  "grade": 90.0   // computed field
}

The computed field is in the response, as expected.

However, the computed field is not being added to the json schema:

{
  "openapi": "3.1.0",
  "info": {
    "title": "FastAPI",
    "version": "0.1.0"
  },
  "paths": {
    "/": {
      "get": {
        "summary": "Sample",
        "operationId": "sample__get",
        "responses": {
          "200": {
            "description": "Successful Response",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/StudentGrades"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "StudentGrades": {
        "properties": {
          "english": {
            "type": "integer",
            "title": "English"
          },
          "history": {
            "type": "integer",
            "title": "History"
          },
          "geography": {
            "type": "integer",
            "title": "Geography"
          }
        },
        "type": "object",
        "required": [
          "english",
          "history",
          "geography"
        ],
        "title": "StudentGrades"
      }
    }
  }
}

And therefore, not showing in Swagger UI:

Operating System

Windows, macOS

Operating System Details

No response

FastAPI Version

0.100.0

Python Version

Python 3.10.11

Additional Context

I initially thought this was an issue on Pydantic, and i even opend an issue

But as explained there, the computed field appears when using model_json_schema(mode='serialization'), and not without it.

[ac130kz]

cached_property shows up in the example, but not in the schema for me. Why not make this an issue?

[Kludex]

@tiangolo is already aware of this. This will shortly be supported.

[carlosdorneles-mb]

In FastAPI 0.111.0, fields with the computed_field decorator are not appearing in the documentation.

    @computed_field(description="Operation type group.", examples=OperationGroupTypeEnum.get_values())
    @property
    def type_group(self) -> str:
        return self.type.group

[asparagusbeef]

In FastAPI 0.111.0, fields with the computed_field decorator are not appearing in the documentation.

    @computed_field(description="Operation type group.", examples=OperationGroupTypeEnum.get_values())
    @property
    def type_group(self) -> str:
        return self.type.group

I am having a reverse issue. the computed_field appears in the documentation but not in the actual response.

[filias]

In FastAPI 0.111.0, fields with the computed_field decorator are not appearing in the documentation.

    @computed_field(description="Operation type group.", examples=OperationGroupTypeEnum.get_values())
    @property
    def type_group(self) -> str:
        return self.type.group

This is still valid for me. Will there be any fix or do we need to change anything in our code?

[xiaoling]

In FastAPI 0.111.0, fields with the computed_field decorator are not appearing in the documentation.

    @computed_field(description="Operation type group.", examples=OperationGroupTypeEnum.get_values())
    @property
    def type_group(self) -> str:
        return self.type.group

and not in the response of /api/v1/openapi.json
cc @tiangolo @Kludex 🙏

[PHvL]

In FastAPI 0.111.0, fields with the computed_field decorator are not appearing in the documentation.

    @computed_field(description="Operation type group.", examples=OperationGroupTypeEnum.get_values())
    @property
    def type_group(self) -> str:
        return self.type.group

Are you using separate_input_output_schemas=False? This seems to use validation instead of serialization schema.

[rossmacarthur]

In the API route __init__ the following code is called for

            self.response_field = create_response_field(
                name=response_name,
                type_=self.response_model,
                # TODO: This should actually set mode='serialization', just, that changes the schemas
                # mode="serialization",
                mode="validation",
            )

Is it possible mode could be configurable? Or is the plan to make it the default

[tiangolo]

Yep, that was the change in the internal code ...plus some other thousand lines of test updates.