`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

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 | 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 | GraphQLObjectType[]
  resolveType?: (value: any, info?: GraphQLResolveInfo) => GraphQLObjectType
  description?: string
}
 
type GraphQLObjectsThunk = () => 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: GraphQLInputObjectConfig)
}
 
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(PersonType) },
    children: { type: new GraphQLList(PersonType) }
  })
})

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

let GraphQLInt: GraphQLScalarType

A GraphQLScalarType that represents an int.

GraphQLFloat

let GraphQLFloat: GraphQLScalarType

A GraphQLScalarType that represents a float.

GraphQLString

let GraphQLString: GraphQLScalarType

A GraphQLScalarType that represents a string.

GraphQLBoolean

let GraphQLBoolean: GraphQLScalarType

A GraphQLScalarType that represents a boolean.

GraphQLID

let GraphQLID: GraphQLScalarType

A GraphQLScalarType that represents an ID.

graphql/language graphql/utilities