Backport generic methods to CE

Allow to fetch all pipelines for every projects in a group and its
subgroups.
Allow to fetch the latest pipeline id for each projects of a group and
its subgroups.

app/models/ci/pipeline.rb

@@ -238,6 +238,10 @@ module Ci
       end
     end
+    def self.latest_successful_ids_per_project
+      success.group(:project_id).select('max(id) as id')
+    end
+
     def self.truncate_sha(sha)
       sha[0...8]
     end

app/models/namespace.rb

@@ -232,6 +232,12 @@ class Namespace < ActiveRecord::Base
     Project.inside_path(full_path)
   end
+  # Includes pipelines from this namespace and pipelines from all subgroups
+  # that belongs to this namespace
+  def all_pipelines
+    Ci::Pipeline.where(project: all_projects)
+  end
+
   def has_parent?
     parent.present?
   end

spec/models/ci/pipeline_spec.rb

@@ -1148,6 +1148,19 @@ describe Ci::Pipeline, :mailer do
     end
   end
+  describe '.latest_successful_ids_per_project' do
+    let(:projects) { create_list(:project, 2) }
+    let!(:pipeline1) { create(:ci_pipeline, :success, project: projects[0]) }
+    let!(:pipeline2) { create(:ci_pipeline, :success, project: projects[0]) }
+    let!(:pipeline3) { create(:ci_pipeline, :failed, project: projects[0]) }
+    let!(:pipeline4) { create(:ci_pipeline, :success, project: projects[1]) }
+
+    it 'returns expected pipeline ids' do
+      expect(described_class.latest_successful_ids_per_project)
+        .to contain_exactly(pipeline2, pipeline4)
+    end
+  end
+
   describe '.internal_sources' do
     subject { described_class.internal_sources }

spec/models/namespace_spec.rb

@@ -562,6 +562,17 @@ describe Namespace do
     it { expect(group.all_projects.to_a).to match_array([project2, project1]) }
   end
+  describe '#all_pipelines' do
+    let(:group) { create(:group) }
+    let(:child) { create(:group, parent: group) }
+    let!(:project1) { create(:project_empty_repo, namespace: group) }
+    let!(:project2) { create(:project_empty_repo, namespace: child) }
+    let!(:pipeline1) { create(:ci_empty_pipeline, project: project1) }
+    let!(:pipeline2) { create(:ci_empty_pipeline, project: project2) }
+
+    it { expect(group.all_pipelines.to_a).to match_array([pipeline1, pipeline2]) }
+  end
+
   describe '#share_with_group_lock with subgroups', :nested_groups do
     context 'when creating a subgroup' do
       let(:subgroup) { create(:group, parent: root_group )}