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2017-02-07/README.md

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+# GraphQL Schema Language Cheat Sheet
+The definitive guide to express your GraphQL schema succinctly
+
+_Last updated: 2017-01-28_
+
+_Prepared by: Hafiz Ismail / @sogko_
+
+## What is GraphQL [Schema Language](http://graphql.org/learn/schema/#type-language)?
+
+It is a shorthand notation to succinctly express the basic shape of your GraphQL schema and its type system.
+
+---
+
+## What does it look like?
+
+Below is an example of a typical GraphQL schema expressed in shorthand.
+
+```graphql
+# define E#ntity interface
+interface Entity {
+  id: ID!
+  name: String
+}
+
+## define custom Url Scalar
+scalar Url
+
+## User type implements Entity interface
+type User implements Entity {
+  id: ID!
+  name: String
+  age: Int
+  balance: Float
+  is_active: Boolean
+  friends: [User]!
+  homepage: Url
+}
+
+## root Query type
+type Query {
+  me: User
+  friends(limit: Int = 10): [User]!
+}
+
+## custom complex input type
+input ListUsersInput {
+  limit: Int
+  since_id: ID
+}
+
+## root mutation type
+type Mutation {
+  users(params: ListUsersInput): [User]!
+}
+
+## GraphQL root schema type
+schema {
+  query: Root
+  mutation: Mutation
+  subscription: ...
+}
+```
+
+## Schema
+
+| keyword        | definition                              |
+|----------------|-----------------------------------------|
+| `schema`       | GraphQL schema definition               |
+| `query`        | A read-only fetch operation             |
+| `mutation`     | A write followed by a fetch operation   |
+| `subscription` | A subscription operation (experimental) |
+
+## [Built-in Scalar Types](http://graphql.org/learn/schema/#scalar-types)
+
+| keyword   | definition                                                                                                                                                                                                                                                 |
+|-----------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `Int`     | A signed 32‐bit integer                                                                                                                                                                                                                                    |
+| `Float`   | A signed double-precision floating-point value                                                                                                                                                                                                             |
+| `String`  | A UTF‐8 character sequence                                                                                                                                                                                                                                 |
+| `Boolean` | `true` or `false`                                                                                                                                                                                                                                          |
+| `ID`      | The ID scalar type represents a unique identifier, often used to refetch an object or as the key for a cache. The ID type is serialized in the same way as a String; however, defining it as an ID signifies that it is not intended to be human‐readable. |
+
+## Type Definitions
+
+| keyword     | definition                                                                                              |
+|-------------|---------------------------------------------------------------------------------------------------------|
+| `scalar`    | Represent the leaves of the query (values of fields)                                                    |
+| `type`      | Simple [object](http://graphql.org/learn/schema/#object-types-and-fields) with fields                                                                               |
+| `interface` | Abstract type that includes a certain set of fields that a type must include to implement the interface |
+| `union`     | Similar to interfaces, but without specifing common fields between types                                |
+| `enum`      | A special kind of scalar that is restricted to a particular set of allowed values                       |
+| `input`     | Represent non-scalars for arguments                                                                     |
+
+## [Type Modifiers](http://graphql.org/learn/schema/#lists-and-non-null)
+
+| keyword      | definition                                |
+|--------------|-------------------------------------------|
+| `String`     | Nullable string                           |
+| `String!`    | Non-nullable string                       |
+| `[String]`   | List of nullable strings                  |
+| `[String]!`  | Non-nullable list of nullable strings     |
+| `[String!]!` | Non-nullable list of non-nullable strings |
+
+## [Input Arguments](http://graphql.org/learn/schema/#arguments)
+
+### Basic input
+
+```graphql
+type Query {
+  users(limit: Int): [User]!
+}
+```
+
+### Input with default value
+
+```graphql
+type Query {
+  users(limit: Int = 10): [User]
+}
+```
+
+### Input with multiple args
+
+```graphql
+type Query {
+  users(limit: Int, sort: String): [User]
+}
+```
+
+### Input with multiple args and default values
+
+```graphql
+type Query {
+  users(limit: Int = 10, sort: String): [User]
+}
+
+## or
+
+type Query {
+  users(limit: Int, sort: String = "asc" ): [User]
+}
+
+## or
+
+type Query {
+  users(limit: Int = 10, sort: String = "asc" ): [User]
+}
+```
+
+## [Input Types](http://graphql.org/learn/schema/#input-types)
+
+```graphql
+input ListUsersInput {
+  limit: Int
+  since_id: ID
+}
+
+type Mutation {
+  users(params: ListUsersInput): [Users]!
+}
+```
+
+## [Custom Scalar](http://graphql.org/learn/schema/#scalar-types)
+
+```graphql
+scalar Url
+
+type User {
+  name: String
+  homepage: Url
+}
+```
+
+## [Interfaces](http://graphql.org/learn/schema/#interfaces)
+
+Object implementing one or more interfaces
+```graphql
+interface Foo {
+  is_foo: Boolean
+}
+
+interface Goo {
+  is_goo: Boolean
+}
+
+type Bar implements Foo {
+  is_foo: Boolean
+  is_bar: Boolean
+}
+
+type Bar implements Foo, Goo {
+  is_foo: Boolean
+  is_goo: Boolean
+  is_bar: Boolean
+}
+```
+
+## [Unions](http://graphql.org/learn/schema/#union-types)
+
+Union of one or more objects
+
+```graphql
+type Foo {
+  name: String
+}
+
+type Bar {
+  is_bar: String
+}
+
+union SingleUnion = Foo
+union MultipleUnion = Foo | Bar
+
+type Root {
+  single: SingleUnion
+  multiple: MultipleUnion
+}
+```
+
+## [Enums](http://graphql.org/learn/schema/#enumeration-types)
+
+```graphql
+enum USER_STATE {
+  NOT_FOUND
+  ACTIVE
+  INACTIVE
+  SUSPENDED
+}
+
+type Root {
+  stateForUser(userID: ID!): USER_STATE!
+  users(state: USER_STATE, limit: Int = 10): [User]
+}
+```