Ruby On Rails and GraphQL Part 2

As a second installment to my last post, here is a guide on how to use GraphQL to get all posts by a user and how to get all comments with our post.

First off, we need to create a comments table:

rails g resource Comment content:text user:references post:references
rails db:migrate

Now we need to go in and add the has_many part of the relationships with the posts and users:

# /app/models/post.rb class
Post < ApplicationRecord 
  belongs_to :user
  has_many :comments 
end 
#app/models/user.rb
class User < ApplicationRecord 
  has_many :posts
  has_many :comments
end

Next we need to run a GraphQL generator:

rails g graphql:object comment

After that generator, we should be able to see a new type in /app/graphql/types named comment_type.rb. Let’s edit post_type.rb to add our comments to it.

# /app/graphql/types/post_type.rb
module Types 
  class PostType < Types::BaseObject 
    field :id, ID, null: false
    field :title, String, null: true
    field :content, String, null: true
    field :user, Types::UserType, null: false
   # new code
    field :comments, [Types::CommentType], null: true
   # end new code
    field :created_at, GraphQL::Types::ISO8601DateTime, null: false     
    field :updated_at, GraphQL::Types::ISO8601DateTime, null: false     
  end
end

The brackets around the type tell GraphQL that we want an array of comments, not just one, which makes sense with our has_many relationship.

If you followed the last guide, we generated some posts already, so lets add some comments to that. In the console run the following:

rails c

Comment.create(post_id: 1, content: ‘this is a comment’, user_id: 1)

Comment.create(post_id: 2, content: ‘this is a comment’, user_id: 1)

Comment.create(post_id: 1, content: ‘this is another comment by a different user’, user_id: 2)

Now if you submit the following GraphQL query:

{
  posts {
    title,
    content,
    comments { 
      content
    }
  }
}

You should get this result!

Now let’s add the username to those comments. Keep in mind that the following will create an N+1 situation for you. There are ways to help with this, and I may cover those in future blog posts, but it is beyond the scope of this article.

It’s simply a matter of adding the user type to our comment type:

module Types
  class CommentType < Types::BaseObject
    field :id, ID, null: false
    field :content, String, null: true
  # replace the user_id field with the following
    field :user, Types::UserType, null: false
    field :post_id, Integer, null: false
    field :created_at, GraphQL::Types::ISO8601DateTime, null: false
    field :updated_at, GraphQL::Types::ISO8601DateTime, null: false
  end
end

That’s it! Try the following query out now:

{
  posts {
    title,
    content,
    comments { 
      content, 
      user {
        username
      }
    }
  }
}

And here is the result:

Let’s get all the posts by a user. This one is easy too!

Change your query type file to the following:

module Types
  class QueryType < Types::BaseObject
    field :users, [Types::UserType], null: false
    field :posts, [Types::PostType], null: false do
      argument :user_id, ID, required: false
    end
    field :post, Types::PostType, null: false do
      argument :id, ID, required: true
    end
   def post(id:)
      Post.find(id)
    end
   def posts(args)
      if args
        Post.where(args)
      else
        Post.all
      end
    end
   def users
      User.all
    end
  end
end

If you submit the following query, you should see the posts by first_user:

query ($userId: ID) { 
  posts (userId: $userId) {
    title,
    content,
    comments {
       content,
       user { 
         username
       }
    }
  }
}

With variables set as:

{
  "userId": 1
}

Good job, you did it! Happy Coding!