List custom integration projects

I've created a new concern to add specific methods related to
integrations.

app/controllers/concerns/integrations_actions.rb

@@ -36,6 +36,10 @@ module IntegrationsActions
     end
   end
 
+  def custom_integration_projects
+    Project.with_custom_integration_compared_to(integration).page(params[:page]).per(20)
+  end
+
   def test
     render json: {}, status: :ok
   end

app/models/concerns/integration.rb

+# frozen_string_literal: true
+
+module Integration
+  extend ActiveSupport::Concern
+
+  class_methods do
+    def with_custom_integration_compared_to(integration)
+      custom_integrations = Service
+        .select('1')
+        .where(type: integration.type, inherit_from_id: nil)
+        .where('services.project_id = projects.id')
+
+      Project.where('EXISTS (?)', custom_integrations)
+    end
+  end
+end

app/models/project.rb

@@ -33,6 +33,7 @@ class Project < ApplicationRecord
   include OptionallySearch
   include FromUnion
   include IgnorableColumns
+  include Integration
   extend Gitlab::Cache::RequestCache
 
   extend Gitlab::ConfigHelper

config/routes/admin.rb

@@ -118,6 +118,7 @@ namespace :admin do
     resources :services, only: [:index, :edit, :update]
     resources :integrations, only: [:edit, :update] do
       member do
+        get :custom_integration_projects
         put :test
       end
     end

spec/controllers/admin/integrations_controller_spec.rb

@@ -4,6 +4,7 @@ require 'spec_helper'
 
 describe Admin::IntegrationsController do
   let(:admin) { create(:admin) }
+  let(:integration) { create(:jira_service, :instance) }
 
   before do
     sign_in(admin)
@@ -33,8 +34,6 @@ describe Admin::IntegrationsController do
   end
 
   describe '#update' do
-    let(:integration) { create(:jira_service, :instance) }
-
     before do
       allow(PropagateIntegrationWorker).to receive(:perform_async)
 
@@ -68,4 +67,14 @@ describe Admin::IntegrationsController do
       end
     end
   end
+
+  describe '#custom_integration_projects' do
+    it 'calls to get the custom integration projects' do
+      allow(Project).to receive_message_chain(:with_custom_integration_compared_to, :page, :per)
+
+      get :custom_integration_projects, params: { id: integration.class.to_param }
+
+      expect(Project).to have_received(:with_custom_integration_compared_to).with(integration)
+    end
+  end
 end

spec/models/integration_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Integration do
+  let(:project_1) { create(:project) }
+  let(:project_2) { create(:project) }
+  let(:instance_integration) { create(:jira_service, :instance) }
+
+  before do
+    create(:jira_service, project: project_1, inherit_from_id: instance_integration.id)
+    create(:jira_service, project: project_2, inherit_from_id: nil)
+    create(:slack_service, project: project_1, inherit_from_id: nil)
+  end
+
+  describe '#with_custom_integration_compared_to' do
+    it 'returns projects with custom integrations' do
+      expect(Project.with_custom_integration_compared_to(instance_integration)).to contain_exactly(project_2)
+    end
+  end
+end