Graphql

Introduction

This is a query language for your API.

Example

A example Query and Response provides an example. It is used by

• Facebook
• PsyPal
• Twitter
• Github

Core Concepts

Data Types

• Int signed 32-bit integer
• Float signed double-precision floating-point value
• String utf8 character sequence
• Boolean true or false values
• ID Unique identifier, Used to re-fetch an object or a the key for a cache

Structure Types

type Author {
  id: ID,
  firstName: String
  lastName: String
  rating: Float
  numOfCourses: Int
}

Enums

enum language {
  ENGLISH
  SPANISH
  FRENCH
}

Query and Mutation Types

Every GraphQL service has a query type. It may or may not have a mutation type. Tyey act as an entry point into the schema.

schema {
  query: Query
  mutation: Mutation
}

Examples

type Query {
   author_details: [Author]
}

type Mutation {
   addAuthor: [firstName: String, lastName: String_):Author
}

Allowing Null values

Adding a bang to the fields means the field is allowed to be nullable.

type Author {
  id: ID!,
  firstName: String
  lastName: String
  rating: Float
  numOfCourses: Int
}

Queries

Arguments

Creating queries is straight forward

query viewInfo {
    viewer {
        login
        bio
        id
        name
        followers (last : 3) {
           nodes {
              id,
              bio
           }
        } 
    }
}

Alias

To prevent duplicate returned data names you need to add aliases.

query viewInfo {
    viewer {
        login
        bio
        id
        name
        firstfollowers: followers (first : 3) {
           nodes {
              id,
              bio
           }
        }
        lastfollowers: followers (last : 3) {
           nodes {
              id,
              bio
           }
        } 
    }
}

Fragments

To make query less duplicated you can write macros and use the eclipse.

query viewInfo {
    viewer {
        login
        bio
        id
        name
        firstfollowers: followers (first : 3) {
           nodes {
              ...userInfo
           }
        }
        lastfollowers: followers (last : 3) {
           nodes {
              ...userInfo
           }
        } 
    }
}

fragment userInfo on User {
    id
    bio
    bioHTML

Operation Names

This is just the name given to the query, in out case viewerInfo.

Variables

Add to the input with brackets and use specifying the field. e.g.

query viewInfo($isOwner: Boolean!) {
    viewer {
        login
        bio
        id
        name
        starredRepositories(ownedByViewer: $isOwner, last 5) {
           nodes {
              ...userInfo
           }
        }
    }
}

Mutations

Intro

• Mutation are used to make changes to the data (Create, update, delete data)
• GraphQL assume side-effects after mutations and changes the dataset after a mutation
• While query fields are executed in parallel, mutation fields are run in series. one after the other.

Example

Below is an example mutation

mutation NewStatus($input: ChangeUserStatusInput!) {
    changeUserStatus(input: $input) {
        clientMutationId
        status {
            message
        }
    }
}

query viewInfo($isOwner: Boolean!) {
    viewer {
        login
        name
        status {
           id
           message
        }
    }
}

Input data.

{
    "input" : {
        "clientMuationId": "10101020",
        "message": "Demo message"
    }
}

GraphQL Ecosystem and Tooling

GraphQL Clients

• Apollo client (Used in Angular and Vue)
• Relay (Facebook use this in React)

GraphQL Server

• Apollo Server
• Express GraphQL
• GraphQL yoga

Tools

• GraphiQL An in-browswer IDE for writing and testing GraphQL queries
• GraphQL Voyager Represents any GraphQL API as an interactive graph
• GraphQL Faker Mocks your API and realistic data
• GraphQL Visual Editor Create schemas