Getting Started

Overview

• An alternative approach to RESTful APIs
• GraphQL is a query language for APIs
• Easily describe the shape of the GraphQL API using clear shared terms.
• Clients issue queries/mutations to read and update data
• GraphQL syntax can express complex entity relations
• Libraries to implement GraphQL in different languages

GraphQL

Schema

schema	GraphQL schema definition
query	Read and traverse data
mutation	Modify data or trigger an action
subscription	Run a query when an event occurs

Built-in Scalar Types

Int	Signed 32‐bit integer
Float	Signed double-precision floating-point value
String	UTF‐8 character sequence
Boolean	true or false
ID	A Unique identifier

Type Definitions

scalar	Scalar Type
type	Object Type
interface	Interface Type
union	Union Type
enum	Enum Type
input	Input Object Type

Type Modifiers

String	Nullable String
String!	Non-null String
[String]	List of nullable Strings
[String]!	Non-null list of nullable Strings
[String!]!	Non-null list of non-null Strings

Input Arguments

Basic Input

type Query {
    users(limit: Int): [User]
}

Input with default value

type Query {
    users(limit: Int = 10): [User]
}

Input with multiple arguments

type Query {
    users(limit: Int, sort: String): [User]
}

Input with multiple arguments and default values

type Query {
    users(limit: Int = 10, sort: String): [User]
}
type Query {
    users(limit: Int, sort: String = "asc"): [User]
}
type Query {
    users(limit: Int = 10, sort: String = "asc"): [User]
}

Input Types

input ListUsersInput {
    limit: Int
    since_id: ID
}

type Mutation {
    users(params: ListUsersInput): [User]!
}

Custom Scalars

scalar Url
type User {
    name: String
    homepage: Url
}

Interfaces

interface Foo {
    is_foo: Boolean
}
interface Goo {
    is_goo: Boolean
}
type Bar implements Foo {
    is_foo: Boolean
    is_bar: Boolean
}
type Baz implements Foo, Goo {
    is_foo: Boolean
    is_goo: Boolean
    is_baz: Boolean
}

Object implementing one or more Interfaces

Unions

type Foo {
    name: String
}
type Bar {
    is_bar: String
}
union SingleUnion = Foo
union MultipleUnion = Foo | Bar
type Root {
    single: SingleUnion
    multiple: MultipleUnion
}

Union of one or more Objects

Enums

enum USER_STATE {
    NOT_FOUND
    ACTIVE
    INACTIVE
    SUSPENDED
}
type Root {
    stateForUser(userID: ID!): USER_STATE!
    users(state: USER_STATE, limit: Int = 10): [User]
}

Also see

• GraphQL Schema Language Cheat Sheet (github.com)