scalar-already-registered.md

title
Scalar already registered Error

Scalar already registered Error

Description

This error is thrown when trying to use a scalar that is already registered. This usually happens when using the same name for different scalars, for example the following code will throw this error:

import strawberry
from typing import NewType
from strawberry.schema.config import StrawberryConfig

MyCustomScalar = NewType("MyCustomScalar", str)
MyCustomScalar2 = NewType("MyCustomScalar2", int)


@strawberry.type
class Query:
    scalar_1: MyCustomScalar
    scalar_2: MyCustomScalar2


strawberry.Schema(
    Query,
    config=StrawberryConfig(
        scalar_map={
            MyCustomScalar: strawberry.scalar(
                name="MyCustomScalar", serialize=str, parse_value=str
            ),
            MyCustomScalar2: strawberry.scalar(
                name="MyCustomScalar", serialize=int, parse_value=int
            ),
        }
    ),
)

This happens because different types in Strawberry (and GraphQL) cannot have the same name.

This error might happen also when trying to defined a scalar with the same name as a type.

How to fix this error

You can fix this error by either reusing the existing scalar, or by changing the name of one of them, for example in this code we renamed the second scalar:

import strawberry
from typing import NewType
from strawberry.schema.config import StrawberryConfig

MyCustomScalar = NewType("MyCustomScalar", str)
MyCustomScalar2 = NewType("MyCustomScalar2", int)


@strawberry.type
class Query:
    scalar_1: MyCustomScalar
    scalar_2: MyCustomScalar2


strawberry.Schema(
    Query,
    config=StrawberryConfig(
        scalar_map={
            MyCustomScalar: strawberry.scalar(
                name="MyCustomScalar", serialize=str, parse_value=str
            ),
            MyCustomScalar2: strawberry.scalar(
                name="MyCustomScalar2", serialize=int, parse_value=int
            ),
        }
    ),
)