foo.rb

class ArticleEntity < ArticleCommonEntity; end
  def as_json
    {id: @article.id, thumbnail_url: @article.thumbnail_url}
  end
end

get "/articles" do
  Article.all.map {|a| ArticleEntity.new(a) }.to_json
end

get "/articles/:id" do
  ArticleEntity.new(Article.find(params[:id]).to_json
end

class ArticleListEntity < ArticleCommonEntity; end
class ArticleDetailEntity < ArticleCommonEntity;
  def as_json
    super.merge(thumbnail_url: @article.thumbnail_url)
  end
end

get "/articles" do
  Article.all.map {|a| ArticleListEntity.new(a) }.to_json
end

get "/articles/:id" do
  ArticleDetailEntity.new(Article.find(params[:id]).to_json
end

post "/graphql" do
  query = QueryStore.get(params[:query_id])

  AppSchema.execute(query).to_json
end

post "/graphql" do
  AppSchema.execute(params[:query]).to_json
end

class ArticleType < GraphQL::Schema::Object
  field :id, ID, null: false
  field :title, String, null: false
  field :thumbnail_url, String, null: false
end

class QueryType < Types::BaseObject
  field :articles, [ArticleType], null: true
  field :article, ArticleType, null: true do
    argument :id, ID, required: true
  end

  def articles; Article.all; end
  def article(id:); Article.find(id); end
end

class AppSchema < GraphQL::Schema
  query QueryType
end

post "/graphql" do
  AppSchema.execute(params[:query], params[:variables]).to_json
end

get "/articles" do
  AppSchema.execute(<<~GQL).to_json
    query {
      articles {
        id, title
      }
    }
  GQL
end

get "/articles/:id" do
  AppSchema.execute(<<~GQL, {id: params[:id]}).to_json
    query getArticle($id: ID!) {
      article(id: $id) {
        id, title, thumbnail_url
      }
    }
  GQL
end