Avoid plucking Todo ids and use sub-queries instead

TodoService should not call `.select(&:id)` on todos, because this is
bad performance. So instead use sub-queries, which will result in a
single SQL query to the database.

https://docs.gitlab.com/ee/development/sql.html#plucking-ids

app/controllers/dashboard/todos_controller.rb

@@ -13,7 +13,7 @@ class Dashboard::TodosController < Dashboard::ApplicationController
   end
   def destroy
-    TodoService.new.mark_todos_as_done_by_ids([params[:id]], current_user)
+    TodoService.new.mark_todos_as_done_by_ids(params[:id], current_user)
     respond_to do |format|
       format.html do
@@ -37,7 +37,7 @@ class Dashboard::TodosController < Dashboard::ApplicationController
   end
   def restore
-    TodoService.new.mark_todos_as_pending_by_ids([params[:id]], current_user)
+    TodoService.new.mark_todos_as_pending_by_ids(params[:id], current_user)
     render json: todos_counts
   end

app/services/issuable_base_service.rb

@@ -288,7 +288,7 @@ class IssuableBaseService < BaseService
       todo_service.mark_todo(issuable, current_user)
     when 'done'
       todo = TodosFinder.new(current_user).execute.find_by(target: issuable)
-      todo_service.mark_todos_as_done([todo], current_user) if todo
+      todo_service.mark_todos_as_done_by_ids(todo, current_user) if todo
     end
   end

app/services/todo_service.rb

@@ -170,20 +170,22 @@ class TodoService
   # When user marks some todos as done
   def mark_todos_as_done(todos, current_user)
-    update_todos_state_by_ids(todos.select(&:id), current_user, :done)
+    update_todos_state(todos, current_user, :done)
   end
   def mark_todos_as_done_by_ids(ids, current_user)
-    update_todos_state_by_ids(ids, current_user, :done)
+    todos = todos_by_ids(ids, current_user)
+    mark_todos_as_done(todos, current_user)
   end
   # When user marks some todos as pending
   def mark_todos_as_pending(todos, current_user)
-    update_todos_state_by_ids(todos.select(&:id), current_user, :pending)
+    update_todos_state(todos, current_user, :pending)
   end
   def mark_todos_as_pending_by_ids(ids, current_user)
-    update_todos_state_by_ids(ids, current_user, :pending)
+    todos = todos_by_ids(ids, current_user)
+    mark_todos_as_pending(todos, current_user)
   end
   # When user marks an issue as todo
@@ -198,9 +200,11 @@ class TodoService
   private
-  def update_todos_state_by_ids(ids, current_user, state)
-    todos = current_user.todos.where(id: ids)
+  def todos_by_ids(ids, current_user)
+    current_user.todos.where(id: Array(ids))
+  end
+  def update_todos_state(todos, current_user, state)
     # Only update those that are not really on that state
     todos = todos.where.not(state: state)
     todos_ids = todos.pluck(:id)

changelogs/unreleased/tc-no-todo-service-select.yml

+---
+title: Avoid plucking Todo ids in TodoService
+merge_request: 10845
+author:

lib/api/todos.rb

@@ -59,10 +59,10 @@ module API
         requires :id, type: Integer, desc: 'The ID of the todo being marked as done'
       end
       post ':id/mark_as_done' do
-        todo = current_user.todos.find(params[:id])
-        TodoService.new.mark_todos_as_done([todo], current_user)
-        present todo.reload, with: Entities::Todo, current_user: current_user
+        TodoService.new.mark_todos_as_done_by_ids(params[:id], current_user)
+        todo = Todo.find(params[:id])
+        present todo, with: Entities::Todo, current_user: current_user
       end
       desc 'Mark all todos as done'

lib/api/v3/todos.rb

@@ -11,10 +11,10 @@ module API
           requires :id, type: Integer, desc: 'The ID of the todo being marked as done'
         end
         delete ':id' do
-          todo = current_user.todos.find(params[:id])
-          TodoService.new.mark_todos_as_done([todo], current_user)
-          present todo.reload, with: ::API::Entities::Todo, current_user: current_user
+          TodoService.new.mark_todos_as_done_by_ids(params[:id], current_user)
+          todo = Todo.find(params[:id])
+          present todo, with: ::API::Entities::Todo, current_user: current_user
         end
         desc 'Mark all todos as done'

spec/services/todo_service_spec.rb

@@ -336,7 +336,7 @@ describe TodoService do
     describe '#mark_todos_as_done' do
       it_behaves_like 'updating todos state', :mark_todos_as_done, :pending, :done do
-        let(:collection) { [first_todo, second_todo] }
+        let(:collection) { Todo.all }
       end
     end
@@ -348,7 +348,7 @@ describe TodoService do
     describe '#mark_todos_as_pending' do
       it_behaves_like 'updating todos state', :mark_todos_as_pending, :done, :pending do
-        let(:collection) { [first_todo, second_todo] }
+        let(:collection) { Todo.all }
       end
     end
@@ -880,14 +880,16 @@ describe TodoService do
     it 'marks an array of todos as done' do
       todo = create(:todo, :mentioned, user: john_doe, target: issue, project: project)
-      expect { described_class.new.mark_todos_as_done([todo], john_doe) }
+      todos = TodosFinder.new(john_doe, {}).execute
+      expect { described_class.new.mark_todos_as_done(todos, john_doe) }
         .to change { todo.reload.state }.from('pending').to('done')
     end
     it 'returns the ids of updated todos' do # Needed on API
       todo = create(:todo, :mentioned, user: john_doe, target: issue, project: project)
-      expect(described_class.new.mark_todos_as_done([todo], john_doe)).to eq([todo.id])
+      todos = TodosFinder.new(john_doe, {}).execute
+      expect(described_class.new.mark_todos_as_done(todos, john_doe)).to eq([todo.id])
     end
     context 'when some of the todos are done already' do
@@ -907,11 +909,32 @@ describe TodoService do
         expect(described_class.new.mark_todos_as_done(Todo.all, john_doe)).to eq([])
       end
     end
+  end
+
+  describe '#mark_todos_as_done_by_ids' do
+    let(:issue) { create(:issue, project: project, author: author, assignees: [john_doe]) }
+    let(:another_issue) { create(:issue, project: project, author: author, assignees: [john_doe]) }
+
+    it 'marks an array of todo ids as done' do
+      todo = create(:todo, :mentioned, user: john_doe, target: issue, project: project)
+      another_todo = create(:todo, :mentioned, user: john_doe, target: another_issue, project: project)
+
+      expect { described_class.new.mark_todos_as_done_by_ids([todo.id, another_todo.id], john_doe) }
+        .to change { john_doe.todos.done.count }.from(0).to(2)
+    end
+
+    it 'marks a single todo id as done' do
+      todo = create(:todo, :mentioned, user: john_doe, target: issue, project: project)
+
+      expect { described_class.new.mark_todos_as_done_by_ids(todo.id, john_doe) }
+        .to change { todo.reload.state }.from('pending').to('done')
+    end
     it 'caches the number of todos of a user', :use_clean_rails_memory_store_caching do
       create(:todo, :mentioned, user: john_doe, target: issue, project: project)
       todo = create(:todo, :mentioned, user: john_doe, target: issue, project: project)
-      described_class.new.mark_todos_as_done([todo], john_doe)
+
+      described_class.new.mark_todos_as_done_by_ids(todo, john_doe)
       expect_any_instance_of(TodosFinder).not_to receive(:execute)