Strawberry Exceptions

    Strawberry defines its library-specific exceptions in strawberry.exceptions.

    Strawberry Schema Exceptions

    FieldWithResolverAndDefaultFactoryError

    This exception is raised when strawberry.field is used with both resolver and default_factory arguments.

    @strawberry.type
    class Query:
    @strawberry.field(default_factory=lambda: "Example C")
    def c(self) -> str:
    return "I'm a resolver"
    # Throws 'Field "c" on type "Query" cannot define a default_factory and a resolver.'

    FieldWithResolverAndDefaultValueError

    This exception is raised when strawberry.field is used with both resolver and default arguments.

    def test_resolver() -> str:
    return "I'm a resolver"
    @strawberry.type
    class Query:
    c: str = strawberry.field(default="Example C", resolver=test_resolver)
    # Throws 'Field "c" on type "Query" cannot define a default value and a resolver.'
    ### MissingTypesForGenericError
    This exception is raised when a `Generic` type is added to the Strawberry Schema without
    passing any type to make it concrete.
    ### MultipleStrawberryArgumentsError
    This exception is raised when `strawberry.argument` is used multiple times in a type
    annotation.
    ```python import strawberry
    from typing_extensions import Annotated
    @strawberry.field
    def name(
    argument: Annotated[
    str,
    strawberry.argument(description="This is a description"),
    strawberry.argument(description="Another description"),
    ]
    ) -> str:
    return "Name"
    # Throws 'Annotation for argument `argument` on field `name` cannot have multiple `strawberry.argument`s'

    UnsupportedTypeError

    This exception is thrown when the type-annotation used is not supported by strawberry.field. At the time of writing this exception is used by Pydantic only

    class Model(pydantic.BaseModel):
    field: pydantic.Json
    @strawberry.experimental.pydantic.type(Model, fields=["field"])
    class Type:
    pass

    WrongNumberOfResultsReturned

    This exception is raised when the DataLoader returns a different number of results than requested.

    async def idx(keys):
    return [1, 2]
    loader = DataLoader(load_fn=idx)
    await loader.load(1)
    # Throws 'Received wrong number of results in dataloader, expected: 1, received: 2'

    Runtime exceptions

    Some errors are also thrown when trying to exectuing queries (mutations or subscriptions).

    MissingQueryError

    This exception is raised when the request is missing the query parameter.

    client.post("/graphql", data={})
    # Throws 'Request data is missing a "query" value'

    UnallowedReturnTypeForUnion

    This error is raised when the return type of a Union is not in the list of Union types.

    @strawberry.type
    class Outside:
    c: int
    @strawberry.type
    class A:
    a: int
    @strawberry.type
    class B:
    b: int
    @strawberry.type
    class Mutation:
    @strawberry.mutation
    def hello(self) -> Union[A, B]:
    return Outside(c=5)
    query = """ mutation { hello { __typename ... on A { a } ... on B { b } } } """
    result = schema.execute_sync(query)
    # result will look like:
    # ExecutionResult(
    # data=None,
    # errors=[
    # GraphQLError(
    # "The type \"<class 'schema.Outside'>\" of the field \"hello\" is not in the list of the types of the union: \"['A', 'B']\"",
    # locations=[SourceLocation(line=3, column=9)],
    # path=["hello"],
    # )
    # ],
    # extensions={},
    # )

    WrongReturnTypeForUnion

    This exception is thrown when the Union type cannot be resolved because it's not a strawberry.field.

    @strawberry.type
    class A:
    a: int
    @strawberry.type
    class B:
    b: int
    @strawberry.type
    class Query:
    ab: Union[A, B] = "ciao" // missing `strawberry.field` !
    query = """{ ab { __typename, ... on A { a } } }"""
    result = schema.execute_sync(query, root_value=Query())
    # result will look like:
    # ExecutionResult(
    # data=None,
    # errors=[
    # GraphQLError(
    # 'The type "<class \'str\'>" cannot be resolved for the field "ab" , are you using a strawberry.field?',
    # locations=[SourceLocation(line=2, column=9)],
    # path=["ab"],
    # )
    # ],
    # extensions={},
    # )

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