Add backend pagination to the environments dashboard

Part of https://gitlab.com/gitlab-org/gitlab/-/issues/33895

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39847

ee/app/controllers/operations_controller.rb

@@ -76,10 +76,13 @@ class OperationsController < ApplicationController
   end
 
   def serialize_as_json(projects)
-    DashboardOperationsSerializer.new(current_user: current_user).represent(projects).as_json
+    DashboardOperationsSerializer.new(current_user: current_user).represent(projects)
   end
 
   def serialize_as_json_for_environments(projects)
-    DashboardEnvironmentsSerializer.new(current_user: current_user).represent(projects).as_json
+    DashboardEnvironmentsSerializer
+      .new(current_user: current_user)
+      .with_pagination(request, response)
+      .represent(projects)
   end
 end

ee/app/serializers/dashboard_environments_serializer.rb

 # frozen_string_literal: true
 
 class DashboardEnvironmentsSerializer < BaseSerializer
+  include WithPagination
+
   entity DashboardEnvironmentsProjectEntity
 end

ee/app/services/dashboard/environments/list_service.rb

@@ -3,8 +3,6 @@
 module Dashboard
   module Environments
     class ListService
-      MAX_NUM_PROJECTS = 7
-
       def initialize(user)
         @user = user
       end
@@ -21,7 +19,7 @@ module Dashboard
       def load_projects(user)
         projects = ::Dashboard::Projects::ListService
           .new(user, feature: :operations_dashboard)
-          .execute(user.ops_dashboard_projects, limit: MAX_NUM_PROJECTS)
+          .execute(user.ops_dashboard_projects)
 
         ActiveRecord::Associations::Preloader.new.preload(projects, [
           :route,

ee/app/services/dashboard/projects/list_service.rb

@@ -3,17 +3,18 @@
 module Dashboard
   module Projects
     class ListService
+      PRESELECT_PROJECTS_LIMIT = 150
+
       def initialize(user, feature:)
         @user = user
         @feature = feature
       end
 
-      def execute(project_ids, include_unavailable: false, limit: nil)
-        return [] unless License.feature_available?(feature)
+      def execute(project_ids, include_unavailable: false)
+        return Project.none unless License.feature_available?(feature)
 
+        project_ids = available_project_ids(project_ids) unless include_unavailable
         projects = find_projects(project_ids)
-        projects = available_projects(projects) unless include_unavailable
-        projects = limit ? projects.first(limit) : projects
 
         projects
       end
@@ -22,8 +23,10 @@ module Dashboard
 
       attr_reader :user, :feature
 
-      def available_projects(projects)
-        projects.select { |project| project.feature_available?(feature) }
+      # see https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39847
+      def available_project_ids(project_ids)
+        projects = Project.with_namespace.id_in(project_ids.first(PRESELECT_PROJECTS_LIMIT))
+        projects.select { |project| project.feature_available?(feature) }.map(&:id)
       end
 
       def find_projects(project_ids)

ee/changelogs/unreleased/33895-expand-supported-number-projects-on-environments-dashboard-by-ad.yml

+---
+title: Add backend pagination to the environments dashboard
+merge_request: 39847
+author:
+type: change

ee/spec/controllers/operations_controller_spec.rb

@@ -400,19 +400,53 @@ RSpec.describe OperationsController do
           expect(last_deployment_json['id']).to eq(deployment.id)
         end
 
-        it 'returns a maximum of seven projects' do
-          projects = Array.new(8).map do
-            project = create(:project)
+        context 'with environments pagination' do
+          shared_examples_for 'environments pagination' do |params, projects_count|
+            specify do
+              get :environments_list, params: params
+
+              expect(response).to have_gitlab_http_status(:ok)
+              expect(response).to match_response_schema('dashboard/operations/environments_list', dir: 'ee')
+              expect(json_response['projects'].count).to eq(projects_count)
+              expect(response).to include_pagination_headers
+            end
+          end
+
+          context 'pagination behaviour' do
+            before do
+              projects = create_list(:project, 8) do |project|
                 project.add_developer(user)
-            project
               end
               user.update!(ops_dashboard_projects: projects)
+            end
 
-          get :environments_list
+            context 'with `per_page`' do
+              it_behaves_like 'environments pagination', { per_page: 7 }, 7
+            end
 
-          expect(response).to have_gitlab_http_status(:ok)
-          expect(response).to match_response_schema('dashboard/operations/environments_list', dir: 'ee')
-          expect(json_response['projects'].count).to eq(7)
+            context 'with `page=1`' do
+              it_behaves_like 'environments pagination', { per_page: 7, page: 1 }, 7
+            end
+
+            context 'with `page=2`' do
+              it_behaves_like 'environments pagination', { per_page: 7, page: 2 }, 1
+            end
+          end
+
+          context 'N+1 queries' do
+            subject { get :environments_list }
+
+            it 'avoids N+1 database queries' do
+              control_count = ActiveRecord::QueryRecorder.new { subject }.count
+
+              projects = create_list(:project, 8) do |project|
+                project.add_developer(user)
+              end
+              user.update!(ops_dashboard_projects: projects)
+
+              expect { subject }.not_to exceed_query_limit(control_count)
+            end
+          end
         end
 
         it 'does not return a project for which the operations dashboard feature is unavailable' do