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.

List¶

import { ObjectType, List } from "graphene-js";

@ObjectType()
class Character {
    @Field(List(String)) appearsIn;
}

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.

For ease of development, we can directly use js lists with one element [].

Like:

import { ObjectType, Field } from "graphene-js";

@ObjectType()
class Character {
    @Field([String]) appearsIn;
}

NonNull¶

import { ObjectType, Field, NonNull } from "graphene-js";

@ObjectType()
class Character {
    @Field(NonNull(String)) name;
}

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.

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