graphql/type

The graphql/type module is responsible for defining GraphQL types and schema. You can import either from the graphql/type module, or from the root graphql module. For example:

import { GraphQLSchema } from 'graphql'; // ES6
var { GraphQLSchema } = require('graphql'); // CommonJS

Overview #

Schema

Definitions

Predicates

Un-modifiers

Scalars

Schema #

GraphQLSchema #

class GraphQLSchema {
  constructor(config: GraphQLSchemaConfig)
}

type GraphQLSchemaConfig = {
  query: GraphQLObjectType;
  mutation?: ?GraphQLObjectType;
}

A Schema is created by supplying the root types of each type of operation, query and mutation (optional). A schema definition is then supplied to the validator and executor.

Example #

var MyAppSchema = new GraphQLSchema({
  query: MyAppQueryRootType
  mutation: MyAppMutationRootType
});

Definitions #

GraphQLScalarType #

class GraphQLScalarType<InternalType> {
  constructor(config: GraphQLScalarTypeConfig<InternalType>)
}

type GraphQLScalarTypeConfig<InternalType> = {
  name: string;
  description?: ?string;
  serialize: (value: mixed) => ?InternalType;
  parseValue?: (value: mixed) => ?InternalType;
  parseLiteral?: (valueAST: Value) => ?InternalType;
}

The leaf values of any request and input values to arguments are Scalars (or Enums) and are defined with a name and a series of serialization functions used to ensure validity.

Example #

var OddType = new GraphQLScalarType({
  name: 'Odd',
  serialize: oddValue,
  parseValue: oddValue,
  parseLiteral(ast) {
    if (ast.kind === Kind.INT) {
      return oddValue(parseInt(ast.value, 10));
    }
    return null;
  }
});

function oddValue(value) {
  return value % 2 === 1 ? value : null;
}

GraphQLObjectType #

class GraphQLObjectType {
  constructor(config: GraphQLObjectTypeConfig)
}

type GraphQLObjectTypeConfig = {
  name: string;
  interfaces?: GraphQLInterfacesThunk | Array<GraphQLInterfaceType>;
  fields: GraphQLFieldConfigMapThunk | GraphQLFieldConfigMap;
  isTypeOf?: (value: any, info?: GraphQLResolveInfo) => boolean;
  description?: ?string
}

type GraphQLInterfacesThunk = () => Array<GraphQLInterfaceType>;

type GraphQLFieldConfigMapThunk = () => GraphQLFieldConfigMap;

// See below about resolver functions.
type GraphQLFieldResolveFn = (
  source?: any,
  args?: {[argName: string]: any},
  context?: any,
  info?: GraphQLResolveInfo
) => any

type GraphQLResolveInfo = {
  fieldName: string,
  fieldNodes: Array<Field>,
  returnType: GraphQLOutputType,
  parentType: GraphQLCompositeType,
  schema: GraphQLSchema,
  fragments: { [fragmentName: string]: FragmentDefinition },
  rootValue: any,
  operation: OperationDefinition,
  variableValues: { [variableName: string]: any },
}

type GraphQLFieldConfig = {
  type: GraphQLOutputType;
  args?: GraphQLFieldConfigArgumentMap;
  resolve?: GraphQLFieldResolveFn;
  deprecationReason?: string;
  description?: ?string;
}

type GraphQLFieldConfigArgumentMap = {
  [argName: string]: GraphQLArgumentConfig;
};

type GraphQLArgumentConfig = {
  type: GraphQLInputType;
  defaultValue?: any;
  description?: ?string;
}

type GraphQLFieldConfigMap = {
  [fieldName: string]: GraphQLFieldConfig;
};

Almost all of the GraphQL types you define will be object types. Object types have a name, but most importantly describe their fields.

When two types need to refer to each other, or a type needs to refer to itself in a field, you can use a function expression (aka a closure or a thunk) to supply the fields lazily.

Note that resolver functions are provided the source object as the first parameter. However, if a resolver function is not provided, then the default resolver is used, which looks for a method on source of the same name as the field. If found, the method is called with (args, context, info). Since it is a method on source, that value can always be referenced with this.

Examples #

var AddressType = new GraphQLObjectType({
  name: 'Address',
  fields: {
    street: { type: GraphQLString },
    number: { type: GraphQLInt },
    formatted: {
      type: GraphQLString,
      resolve(obj) {
        return obj.number + ' ' + obj.street
      }
    }
  }
});

var PersonType = new GraphQLObjectType({
  name: 'Person',
  fields: () => ({
    name: { type: GraphQLString },
    bestFriend: { type: PersonType },
  })
});

GraphQLInterfaceType #

class GraphQLInterfaceType {
  constructor(config: GraphQLInterfaceTypeConfig)
}

type GraphQLInterfaceTypeConfig = {
  name: string,
  fields: GraphQLFieldConfigMapThunk | GraphQLFieldConfigMap,
  resolveType?: (value: any, info?: GraphQLResolveInfo) => ?GraphQLObjectType,
  description?: ?string
};

When a field can return one of a heterogeneous set of types, a Interface type is used to describe what types are possible, what fields are in common across all types, as well as a function to determine which type is actually used when the field is resolved.

Example #

var EntityType = new GraphQLInterfaceType({
  name: 'Entity',
  fields: {
    name: { type: GraphQLString }
  }
});

GraphQLUnionType #

class GraphQLUnionType {
  constructor(config: GraphQLUnionTypeConfig)
}

type GraphQLUnionTypeConfig = {
  name: string,
  types: GraphQLObjectsThunk | Array<GraphQLObjectType>,
  resolveType?: (value: any, info?: GraphQLResolveInfo) => ?GraphQLObjectType;
  description?: ?string;
};

type GraphQLObjectsThunk = () => Array<GraphQLObjectType>;

When a field can return one of a heterogeneous set of types, a Union type is used to describe what types are possible as well as providing a function to determine which type is actually used when the field is resolved.

Example #

var PetType = new GraphQLUnionType({
  name: 'Pet',
  types: [ DogType, CatType ],
  resolveType(value) {
    if (value instanceof Dog) {
      return DogType;
    }
    if (value instanceof Cat) {
      return CatType;
    }
  }
});

GraphQLEnumType #

class GraphQLEnumType {
  constructor(config: GraphQLEnumTypeConfig)
}

type GraphQLEnumTypeConfig = {
  name: string;
  values: GraphQLEnumValueConfigMap;
  description?: ?string;
}

type GraphQLEnumValueConfigMap = {
  [valueName: string]: GraphQLEnumValueConfig;
};

type GraphQLEnumValueConfig = {
  value?: any;
  deprecationReason?: string;
  description?: ?string;
}

type GraphQLEnumValueDefinition = {
  name: string;
  value?: any;
  deprecationReason?: string;
  description?: ?string;
}

Some leaf values of requests and input values are Enums. GraphQL serializes Enum values as strings, however internally Enums can be represented by any kind of type, often integers.

Note: If a value is not provided in a definition, the name of the enum value will be used as its internal value.

Example #

var RGBType = new GraphQLEnumType({
  name: 'RGB',
  values: {
    RED: { value: 0 },
    GREEN: { value: 1 },
    BLUE: { value: 2 }
  }
});

GraphQLInputObjectType #

class GraphQLInputObjectType {
  constructor(config: GraphQLInputObjectTypeConfig)
}

type GraphQLInputObjectConfig = {
  name: string;
  fields: GraphQLInputObjectConfigFieldMapThunk | GraphQLInputObjectConfigFieldMap;
  description?: ?string;
}

type GraphQLInputObjectConfigFieldMapThunk = () => GraphQLInputObjectConfigFieldMap;

type GraphQLInputObjectFieldConfig = {
  type: GraphQLInputType;
  defaultValue?: any;
  description?: ?string;
}

type GraphQLInputObjectConfigFieldMap = {
  [fieldName: string]: GraphQLInputObjectFieldConfig;
};

type GraphQLInputObjectField = {
  name: string;
  type: GraphQLInputType;
  defaultValue?: any;
  description?: ?string;
}

type GraphQLInputObjectFieldMap = {
  [fieldName: string]: GraphQLInputObjectField;
};

An input object defines a structured collection of fields which may be supplied to a field argument.

Using NonNull will ensure that a value must be provided by the query

Example #

var GeoPoint = new GraphQLInputObjectType({
  name: 'GeoPoint',
  fields: {
    lat: { type: new GraphQLNonNull(GraphQLFloat) },
    lon: { type: new GraphQLNonNull(GraphQLFloat) },
    alt: { type: GraphQLFloat, defaultValue: 0 },
  }
});

GraphQLList #

class GraphQLList {
  constructor(type: GraphQLType)
}

A list is a kind of type marker, a wrapping type which points to another type. Lists are often created within the context of defining the fields of an object type.

Example #

var PersonType = new GraphQLObjectType({
  name: 'Person',
  fields: () => ({
    parents: { type: new GraphQLList(Person) },
    children: { type: new GraphQLList(Person) },
  })
});

GraphQLNonNull #

class GraphQLNonNull {
  constructor(type: GraphQLType)
}

A non-null is a kind of type marker, a wrapping type which points to another type. Non-null types enforce that their values are never null and can ensure an error is raised if this ever occurs during a request. It is useful for fields which you can make a strong guarantee on non-nullability, for example usually the id field of a database row will never be null.

Example #

var RowType = new GraphQLObjectType({
  name: 'Row',
  fields: () => ({
    id: { type: new GraphQLNonNull(String) },
  })
});

Predicates #

isInputType #

function isInputType(type: ?GraphQLType): boolean

These types may be used as input types for arguments and directives.

isOutputType #

function isOutputType(type: ?GraphQLType): boolean

These types may be used as output types as the result of fields

isLeafType #

function isLeafType(type: ?GraphQLType): boolean

These types may describe types which may be leaf values

isCompositeType #

function isCompositeType(type: ?GraphQLType): boolean

These types may describe the parent context of a selection set

isAbstractType #

function isAbstractType(type: ?GraphQLType): boolean

These types may describe a combination of object types

Un-modifiers #

getNullableType #

function getNullableType(type: ?GraphQLType): ?GraphQLNullableType

If a given type is non-nullable, this strips the non-nullability and returns the underlying type.

getNamedType #

function getNamedType(type: ?GraphQLType): ?GraphQLNamedType

If a given type is non-nullable or a list, this repeated strips the non-nullability and list wrappers and returns the underlying type.

Scalars #

GraphQLInt #

var GraphQLInt: GraphQLScalarType;

A GraphQLScalarType that represents an int.

GraphQLFloat #

var GraphQLFloat: GraphQLScalarType;

A GraphQLScalarType that represents a float.

GraphQLString #

var GraphQLString: GraphQLScalarType;

A GraphQLScalarType that represents a string.

GraphQLBoolean #

var GraphQLBoolean: GraphQLScalarType;

A GraphQLScalarType that represents a boolean.

GraphQLID #

var GraphQLID: GraphQLScalarType;

A GraphQLScalarType that represents an ID.