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🐛 Fix wrong OpenApi scheme generation for custom models with computed fields in additional responses#12119

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DavideGalilei:fix-responses-model-computed-fields
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🐛 Fix wrong OpenApi scheme generation for custom models with computed fields in additional responses#12119
DavideGalilei wants to merge 3 commits intofastapi:masterfrom
DavideGalilei:fix-responses-model-computed-fields

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@DavideGalilei
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@DavideGalilei DavideGalilei commented Sep 2, 2024

Previously discussed here: @computed_field not showing in OpenAPI Json #9856

📕 Description

  • When using computed fields in a custom Pydantic model, FastAPI incorrectly uses mode="validation" for the additional responses model schema.

  • This causes an issue where the response model is interpreted as an -Input model, thus excluding read-only computed fields from the documentation (note: the fields are correctly returned in the answer even if they are not shown in the documentation).

👀 Example code

from fastapi import FastAPI
from pydantic import BaseModel
from pydantic.fields import computed_field

app = FastAPI()

class Rectangle(BaseModel):
    width: int
    height: int

    @computed_field
    def area(self) -> int:
        return self.width * self.height

@app.get(
    "/rectangle/",
    responses={200: {"model": Rectangle}},
)
async def rectangle() -> Rectangle:
    return Rectangle(width=10, height=5)

❌ Wrong (current) schema

Click to expand

image

{
  "openapi": "3.1.0",
  "info": {
    "title": "FastAPI",
    "version": "0.1.0"
  },
  "paths": {
    "/rectangle/": {
      "get": {
        "summary": "Rectangle",
        "operationId": "rectangle_rectangle__get",
        "responses": {
          "200": {
            "description": "Successful Response",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Rectangle-Input"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "Rectangle-Input": {
        "properties": {
          "width": {
            "type": "integer",
            "title": "Width"
          },
          "height": {
            "type": "integer",
            "title": "Height"
          }
        },
        "type": "object",
        "required": [
          "width",
          "height"
        ],
        "title": "Rectangle"
      },
      "Rectangle-Output": {
        "properties": {
          "width": {
            "type": "integer",
            "title": "Width"
          },
          "height": {
            "type": "integer",
            "title": "Height"
          },
          "area": {
            "type": "integer",
            "title": "Area",
            "readOnly": true
          }
        },
        "type": "object",
        "required": [
          "width",
          "height",
          "area"
        ],
        "title": "Rectangle"
      }
    }
  }
}

✅ Correct (fixed) schema:

Click to expand

image

{
  "openapi": "3.1.0",
  "info": {
    "title": "FastAPI",
    "version": "0.1.0"
  },
  "paths": {
    "/rectangle/": {
      "get": {
        "summary": "Rectangle",
        "operationId": "rectangle_rectangle__get",
        "responses": {
          "200": {
            "description": "Successful Response",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Rectangle"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "Rectangle": {
        "properties": {
          "width": {
            "type": "integer",
            "title": "Width"
          },
          "height": {
            "type": "integer",
            "title": "Height"
          },
          "area": {
            "type": "integer",
            "title": "Area",
            "readOnly": true
          }
        },
        "type": "object",
        "required": [
          "width",
          "height",
          "area"
        ],
        "title": "Rectangle"
      }
    }
  }
}

OpenApi schema diff (wrong ➡️ correct)

18c18
<                   "$ref": "#/components/schemas/Rectangle-Input"
---
>                   "$ref": "#/components/schemas/Rectangle"
29,47c29
<       "Rectangle-Input": {
<         "properties": {
<           "width": {
<             "type": "integer",
<             "title": "Width"
<           },
<           "height": {
<             "type": "integer",
<             "title": "Height"
<           }
<         },
<         "type": "object",
<         "required": [
<           "width",
<           "height"
<         ],
<         "title": "Rectangle"
<       },
<       "Rectangle-Output": {
---
>       "Rectangle": {

💊 Fix

Use mode="serialization" for create_model_field for additional responses model.

🧪 Added tests!

  • All tests pass and the code has been formatted
  • tests/test_additional_responses_custom_model_with_computed_fields.py

@DavideGalilei
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DavideGalilei commented Sep 2, 2024 •
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Edit: I just noticed that this PR might be a duplicate PR of #11517

@alejsdev alejsdev added the bug Something isn't working label Sep 3, 2024
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alejsdev commented Sep 3, 2024

Hi @DavideGalilei, thank you for your interest in contributing to the project! Yes, this is a duplicate. We'll review both PRs in detail later. We currently have a high volume of PRs, we appreciate your patience as we manage the queue. 🙇‍♀️

@flxdot
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flxdot commented Sep 5, 2024

Hi @DavideGalilei, thank you for your interest in contributing to the project! Yes, this is a duplicate. We'll review both PRs in detail later. We currently have a high volume of PRs, we appreciate your patience as we manage the queue. 🙇‍♀️

And the PR is a duplicate of #10895 :)

@svlandeg svlandeg self-assigned this Sep 18, 2024
svlandeg
svlandeg reviewed Sep 18, 2024
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@svlandeg svlandeg left a comment

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Hi @DavideGalilei, thanks for the contribution!

Your fix is correct, but the PR is indeed a duplicate of #11517 and #10895. My suggestion is to merge the earliest PR #10895 and close this one, but I'll leave the final review for Tiangolo.

Thanks again though! 🙏

@tiangolo
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tiangolo commented Oct 12, 2024

Thanks for the interest @DavideGalilei! As @svlandeg was saying, this was handled in #10895. That is now available in FastAPI 0.115.1. So I'll now pass on this one, but thanks for the effort! ☕

@tiangolo tiangolo closed this Oct 12, 2024
@svlandeg svlandeg removed their assignment Feb 19, 2025
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@DavideGalilei @alejsdev @flxdot @tiangolo @svlandeg