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@tiangolo any chance this PR will be reviewed?

Rebuilding a response model is a real problem and cannot actually be done correctly because of aliases and other settings (I guess I've already left a comment about this). In normal code your create it by your own from the other sources that could not be converted automatically so it is actually not needed.

Can we expect this to be reviewed and fixed?

@tiangolo hi! Can you answer on this comment?

#4416 (comment)

Hi!
I have this problem too (
This can greatly degrade performance for the complex models with validators or endpoints that return a large number of items.
In example below get_items endpoint already returns a list of items so it is no need to rebuild response again.
And finally we have response in ~2 second instead of ~1 second.

from typing import List
from uuid import UUID, uuid4

from fastapi import FastAPI
from pydantic import BaseModel, validator

app = FastAPI()

class Data(BaseModel):
    i: int

    @validator("i")
    def validate_i(cls, v):
        sleep(0.1)
        return v

class Item(BaseModel):
    id: UUID
    data: Data

@app.get(
    "/items",
    response_model=List[Item],
)
def get_items():
    return [Item(id=uuid4(), data=Data(i=i)) for i in range(10)]

Thank you!

@tiangolo are there any plans on merging or reimplementing this?

@tiangolo is there any way this PR could be merged?

Updated codes and tests.

When users are using Pydantic v2 (fortunately, most applications should be using v2 by now), this issue doesn’t need much attention.

In v2, field.validate will call type_adapter.validator. If you check its schema, you’ll see that the validator will not revalidate instances of response_model (see reference: revalidate_instances).

[This is part of the validator schema for the AutoIncrement object in the test case]

 SchemaValidator(title="AutoIncrement", validator=Model(
    ModelValidator {
        revalidate: Never,
        validator: ModelFields(
            ModelFieldsValidator {
                fields: [
                    Field {
                        name: "count",
                        lookup_key: Simple {
                            key: "count",
...

Although there are some additional function calls, it won’t trigger the validator in a way that would modify the original response_content value in certain cases.

Therefore, this fix is only relevant for applications that are still using Pydantic v1.

The changes from #14099 are interfering with this PR... 🕵️‍♀️

[UPDATE]: solved ✔️