Remove dependent destroy for project builds

This commit removes the ActiveRecord callback and leverages
the foreign key when deleting builds attached to a project.

app/models/project.rb

@@ -341,12 +341,8 @@ class Project < ApplicationRecord
   has_many :stages, class_name: 'Ci::Stage', inverse_of: :project
   has_many :ci_refs, class_name: 'Ci::Ref', inverse_of: :project
 
-  # Ci::Build objects store data on the file system such as artifact files and
-  # build traces. Currently there's no efficient way of removing this data in
-  # bulk that doesn't involve loading the rows into memory. As a result we're
-  # still using `dependent: :destroy` here.
   has_many :pending_builds, class_name: 'Ci::PendingBuild'
-  has_many :builds, class_name: 'Ci::Build', inverse_of: :project, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :builds, class_name: 'Ci::Build', inverse_of: :project
   has_many :processables, class_name: 'Ci::Processable', inverse_of: :project
   has_many :build_trace_chunks, class_name: 'Ci::BuildTraceChunk', through: :builds, source: :trace_chunks
   has_many :build_report_results, class_name: 'Ci::BuildReportResult', inverse_of: :project

spec/models/concerns/batch_destroy_dependent_associations_spec.rb

@@ -6,10 +6,10 @@ RSpec.describe BatchDestroyDependentAssociations do
   class TestProject < ActiveRecord::Base
     self.table_name = 'projects'
 
-    has_many :builds, dependent: :destroy
+    has_many :builds
     has_many :notification_settings, as: :source, dependent: :delete_all
     has_many :pages_domains
-    has_many :todos
+    has_many :todos, dependent: :destroy
 
     include BatchDestroyDependentAssociations
   end
@@ -18,7 +18,7 @@ RSpec.describe BatchDestroyDependentAssociations do
     let_it_be(:project) { TestProject.new }
 
     it 'returns the right associations' do
-      expect(project.dependent_associations_to_destroy.map(&:name)).to match_array([:builds])
+      expect(project.dependent_associations_to_destroy.map(&:name)).to match_array([:todos])
     end
   end
 
@@ -26,36 +26,35 @@ RSpec.describe BatchDestroyDependentAssociations do
     let_it_be(:project) { create(:project) }
     let_it_be(:build) { create(:ci_build, project: project) }
     let_it_be(:notification_setting) { create(:notification_setting, project: project) }
+    let_it_be(:note) { create(:note, project: project) }
 
-    let!(:todos) { create(:todo, project: project) }
+    it 'destroys multiple notes' do
+      create(:note, project: project)
 
-    it 'destroys multiple builds' do
-      create(:ci_build, project: project)
-
-      expect(Ci::Build.count).to eq(2)
+      expect(Note.count).to eq(2)
 
       project.destroy_dependent_associations_in_batches
 
-      expect(Ci::Build.count).to eq(0)
+      expect(Note.count).to eq(0)
     end
 
-    it 'destroys builds in batches' do
-      expect(project).to receive_message_chain(:builds, :find_each).and_yield(build)
-      expect(build).to receive(:destroy).and_call_original
+    it 'destroys note in batches' do
+      expect(project).to receive_message_chain(:notes, :find_each).and_yield(note)
+      expect(note).to receive(:destroy).and_call_original
 
       project.destroy_dependent_associations_in_batches
 
-      expect(Ci::Build.count).to eq(0)
-      expect(Todo.count).to eq(1)
+      expect(Ci::Build.count).to eq(1)
+      expect(Note.count).to eq(0)
       expect(User.count).to be > 0
       expect(NotificationSetting.count).to eq(User.count)
     end
 
     it 'excludes associations' do
-      project.destroy_dependent_associations_in_batches(exclude: [:builds])
+      project.destroy_dependent_associations_in_batches(exclude: [:notes])
 
+      expect(Note.count).to eq(1)
       expect(Ci::Build.count).to eq(1)
-      expect(Todo.count).to eq(1)
       expect(User.count).to be > 0
       expect(NotificationSetting.count).to eq(User.count)
     end