Another major use case for GraphQL is the integration of multiple existing systems behind a single, coherent GraphQL API. This is particularly compelling for companies with legacy infrastructures and many different APIs that have grown over years and now impose a high maintenance burden. One major problem with these legacy systems is that they make it practically impossible to build innovative products that need access to multiple systems.

In that context, GraphQL can be used to unify these existing systems and hide their complexity behind a nice GraphQL API. This way, new client applications can be developed that simply talk to the GraphQL server to fetch the data they need. The GraphQL server is then responsible for fetching the data from the existing systems and package it up in the GraphQL response format.

Just like in the previous architecture where the GraphQL server didn’t care about the type of database being used, this time it doesn’t care about the data sources that it needs to fetch the data that’s needed to resolve a query.

List:
  query usersQuery {
    photos{
      total
      items{
        id
        url
      }
    } 
  }

Get detail
  query userQuery {
    user(id: 1) {
      id
      name
      username
      email
    }
  }

mutation addUser($name: String, $username: String!, $email: String!, $avatar: String){
createNewUser(input:{
 	name: $name,
  username: $username,
  avatar: $avatar,
  email: $email
}){
  user{
    id
  }
}
}

varialbes:
{
  "name": "Son",
  "username": "sondeptrai",
  "email": "[email protected]",
  "avatar": "http://avatar.com/img.png"
}

config // config env for project
  default.js //default config env 
  development
  production
src
  graphql
    connectors #
      httpConnecttor //defind HTTPConnecttor call to ms-service
      index.js
    errors // To 
      apolloError.js //Show apollo error
      formatError.js
      index.js
      microserviceError.js //Show error when call to ms-service
    models
      ...#You can add more Models look like User
      User
        resolvers //Resolver for schema
          index.js
          mutation.js
          queries.js
          type.js
        schema
          index.js
          schema.gql //Defined schema type
          mutation.gql //Defined Mutation type
          input.gql // Defined Input type
        index.js // Exports resolvers, schema, userList, userModel.js // Defind User class
        userList.js // Defind UserList class
      index.js //Import all models of GraphQL
      root.js //Export rootSchema
      rootSchema.gql Defined all Mutation & Query
    utils
    index.js
  index.js
  plugin.js
  server.js
Dockerfile
docker-compose.yml