Ignored Serializer Error

Description

This error is thrown when a strawberry.pydantic type or interface customizes how its fields are serialized, for example the following code will throw this error:

from datetime import datetime

import pydantic
import strawberry


@strawberry.pydantic.type
class Event(pydantic.BaseModel):
    name: str
    starts_at: datetime

    @pydantic.field_serializer("starts_at")
    def as_date(self, value: datetime) -> str:
        return value.strftime("%Y-%m-%d")  

This happens because GraphQL resolves the fields of Pydantic types from the model’s attributes, not from model_dump() , so the serializer would silently be ignored: startsAt would return the full date and time. Serializers are often used to hide or redact values, so ignoring them could expose data that the model doesn’t show anywhere else.

The same error is thrown for fields with a PlainSerializer or a WrapSerializer , including inside their type, like list[Annotated[str, PlainSerializer(...)]] , for fields with Field(exclude_if=...) , and for models with a @model_serializer . This also includes PlainSerializer and WrapSerializer in exposed computed fields’ return annotations. Fields that aren’t part of the GraphQL type, like strawberry.Private fields, can have serializers, and so can inputs, which aren’t serialized.

How to fix this error

To change the value GraphQL returns, use a field with a resolver, or a custom scalar:

from datetime import date, datetime

import pydantic
import strawberry


@strawberry.pydantic.type
class Event(pydantic.BaseModel):
    name: str
    starts_at: strawberry.Private[datetime]

    @strawberry.pydantic.field
    def starts_on(self) -> date:
        return self.starts_at.date()  

To hide a value, use strawberry.Private or Field(exclude=True) .

There is no configuration option to bypass this check. If serializers are needed for another API, keep them on a separate model rather than on fields exposed by the GraphQL type or interface.