GraphQL

GraphQL is a query language for APIs

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