Lists and Non-Null¶
Object types, scalars, and enums are the only kinds of types you can define in Graphene. But when you use the types in other parts of the schema, or in your query variable declarations, you can apply additional type modifiers that affect validation of those values.
import graphene class Character(graphene.ObjectType): name = graphene.NonNull(graphene.String)
Here, we’re using a
String type and marking it as Non-Null by wrapping
it using the
NonNull class. This means that our server always expects
to return a non-null value for this field, and if it ends up getting a
null value that will actually trigger a GraphQL execution error,
letting the client know that something has gone wrong.
NonNull code snippet is also equivalent to:
import graphene class Character(graphene.ObjectType): name = graphene.String(required=True)
import graphene class Character(graphene.ObjectType): appears_in = graphene.List(graphene.String)
Lists work in a similar way: We can use a type modifier to mark a type as a
List, which indicates that this field will return a list of that type.
It works the same for arguments, where the validation step will expect a list
for that value.