Chap4 Query(READ)

Todo in this chapter

• Implement Query(READ)

Step1. Edit query_type.rb

This is initial graphql/types/query_type.rb file.

module Types
  class QueryType < Types::BaseObject
    # Add root-level fields here.
    # They will be entry points for queries on your schema.

    # TODO: remove me
    field :test_field, String, null: false,
      description: "An example field added by the generator"
    def test_field
      "Hello World!"
    end
  end
end

Add new query field posts

field :posts, [PostType], null: true
def posts
  Post.all
end

So the graphql/types/query_type.rb is...

graphql/types/query_type.rb

module Types
  class QueryType < Types::BaseObject
    # Add root-level fields here.
    # They will be entry points for queries on your schema.

    # TODO: remove me
    field :test_field, String, null: false,
      description: "An example field added by the generator"
    def test_field
      "Hello World!"
    end

    field :posts, [PostType], null: true
    def posts
      Post.all
    end
  end
end

This means...

• field posts is array of PostType and It is ok to return nullable value.
• posts method returns Post.all

Step2. define PostType

Next, We need to define PostType.

https://graphql-ruby.org/getting_started#getting-started

terminal

rails g graphql:object Post title:String body:String

Running via Spring preloader in process 62001
      create  app/graphql/types/post_type.rb

This generates the below code: types/post_type.rb

module Types
  class PostType < Types::BaseObject
    field :title, String, null: true
    field :body, String, null: true
  end
end

Imitate official guide, we will add description and id. https://graphql-ruby.org/getting_started#declare-types

so...

post_type.rb

module Types
  class PostType < Types::BaseObject
    description "A blog post"
    field :id, ID, null: false
    field :title, String, null: false
    field :body, String, null: true
  end
end

​

Step3. Run query from graphiql

Visit: http://api.localhost:3000/graphiql​

Query by using graphiql...

It works!!!

Step4. Recap the flow

(1). query posts from graphiql

​

Check the terminal log!

(2). POST "/graphql" is fired.

(3). It fires GraphqlController#execute action.

terminal

Started POST "/graphql" for 127.0.0.1 at 2019-03-12 15:09:45 +0800
Processing by GraphqlController#execute as */*
  Parameters: {"query"=>"query {\n  posts {\n    id\n    title\n    body\n  }\n}", "variables"=>nil, "subdomain"=>"api", "graphql"=>{"query"=>"query {\n  posts {\n    id\n    title\n    body\n  }\n}", "variables"=>nil}}
  Post Load (0.9ms)  SELECT "posts".* FROM "posts"
  ↳ app/controllers/graphql_controller.rb:10
Completed 200 OK in 40ms (Views: 0.3ms | ActiveRecord: 11.1ms)

(4). In def execute, query is executed.

graphql_controller.rb

class GraphqlController < ApplicationController
  def execute
    variables = ensure_hash(params[:variables])
    query = params[:query]
    operation_name = params[:operationName]
    context = {
      # Query context goes here, for example:
      # current_user: current_user,
    }
    result = RailsApiGraphqlCrudTutoSchema.execute(query, variables: variables, context: context, operation_name: operation_name)
    render json: result
  rescue => e
    raise e unless Rails.env.development?
    handle_error_in_development e
  end
...
end

​

• RailsApiGraphqlCrudTutoSchema is defined in: rails_api_graphql_crud_tuto_schema.rb

  class RailsApiGraphqlCrudTutoSchema < GraphQL::Schema
    mutation(Types::MutationType)
    query(Types::QueryType)
  end
  

• Types::QueryType is defined in: types/query_type.rb

  module Types
    class QueryType < Types::BaseObject
      # Add root-level fields here.
      # They will be entry points for queries on your schema.
  
      # TODO: remove me
      field :test_field, String, null: false,
        description: "An example field added by the generator"
      def test_field
        "Hello World!"
      end
  
      field :posts, [PostType], null: true
      def posts
        Post.all
      end
    end
  end
  

• PostType is defined in: types/post_type.rb

  module Types
    class PostType < Types::BaseObject
      description "A blog post"
      field :id, ID, null: false
      field :title, String, null: false
      field :body, String, null: true
    end
  end
  

So, finally we get the json result!

result

{
  "data": {
    "posts": [
      {
        "id": "1",
        "title": "Death Be Not Proud",
        "body": "Sapiente dignissimos veniam. Et eius velit. Quam dolorem id."
      }
    ]
  }
}

​