Create CTE query for clusters hierarchy

- This enables us to use a scope to query all clusters in group
hierarchy order in one query, and also enables us to union to instance
clusters later.

- Handle case where clusters not present at level. In which case the
query should go ahead and return the next level's clusters.

- Swap with new CTE query behind Feature flag. This FF is default
disabled.

2 files changed, 90 insertions, 1 deletions

diff --git a/spec/models/clusters/clusters_hierarchy_spec.rb b/spec/models/clusters/clusters_hierarchy_spec.rb
new file mode 100644
index 00000000000..0470ebe17ea
--- /dev/null
+++ b/spec/models/clusters/clusters_hierarchy_spec.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Clusters::ClustersHierarchy do
+  describe '#base_and_ancestors' do
+    def base_and_ancestors(clusterable)
+      described_class.new(clusterable).base_and_ancestors
+    end
+
+    context 'project in nested group with clusters at every level' do
+      let!(:cluster) { create(:cluster, :project, projects: [project]) }
+      let!(:child) { create(:cluster, :group, groups: [child_group]) }
+      let!(:parent) { create(:cluster, :group, groups: [parent_group]) }
+      let!(:ancestor) { create(:cluster, :group, groups: [ancestor_group]) }
+
+      let(:ancestor_group) { create(:group) }
+      let(:parent_group) { create(:group, parent: ancestor_group) }
+      let(:child_group) { create(:group, parent: parent_group) }
+      let(:project) { create(:project, group: child_group) }
+
+      it 'returns clusters for project' do
+        expect(base_and_ancestors(project)).to eq([cluster, child, parent, ancestor])
+      end
+
+      it 'returns clusters for child_group' do
+        expect(base_and_ancestors(child_group)).to eq([child, parent, ancestor])
+      end
+
+      it 'returns clusters for parent_group' do
+        expect(base_and_ancestors(parent_group)).to eq([parent, ancestor])
+      end
+
+      it 'returns clusters for ancestor_group' do
+        expect(base_and_ancestors(ancestor_group)).to eq([ancestor])
+      end
+    end
+
+    context 'project in a namespace' do
+      let!(:cluster) { create(:cluster, :project) }
+
+      it 'returns clusters for project' do
+        expect(base_and_ancestors(cluster.project)).to eq([cluster])
+      end
+    end
+
+    context 'project in nested group with clusters at some levels' do
+      let!(:child) { create(:cluster, :group, groups: [child_group]) }
+      let!(:ancestor) { create(:cluster, :group, groups: [ancestor_group]) }
+
+      let(:ancestor_group) { create(:group) }
+      let(:parent_group) { create(:group, parent: ancestor_group) }
+      let(:child_group) { create(:group, parent: parent_group) }
+      let(:project) { create(:project, group: child_group) }
+
+      it 'returns clusters for project' do
+        expect(base_and_ancestors(project)).to eq([child, ancestor])
+      end
+
+      it 'returns clusters for child_group' do
+        expect(base_and_ancestors(child_group)).to eq([child, ancestor])
+      end
+
+      it 'returns clusters for parent_group' do
+        expect(base_and_ancestors(parent_group)).to eq([ancestor])
+      end
+
+      it 'returns clusters for ancestor_group' do
+        expect(base_and_ancestors(ancestor_group)).to eq([ancestor])
+      end
+    end
+  end
+end
diff --git a/spec/models/concerns/deployment_platform_spec.rb b/spec/models/concerns/deployment_platform_spec.rb
index 2378f400540..e2fc8a5d127 100644
--- a/spec/models/concerns/deployment_platform_spec.rb
+++ b/spec/models/concerns/deployment_platform_spec.rb
@@ -5,7 +5,7 @@ require 'rails_helper'
 describe DeploymentPlatform do
   let(:project) { create(:project) }
 
-  describe '#deployment_platform' do
+  shared_examples '#deployment_platform' do
     subject { project.deployment_platform }
 
     context 'with no Kubernetes configuration on CI/CD, no Kubernetes Service' do
@@ -84,4 +84,20 @@ describe DeploymentPlatform do
       end
     end
   end
+
+  context 'legacy implementation' do
+    before do
+      stub_feature_flags(clusters_cte: false)
+    end
+
+    include_examples '#deployment_platform'
+  end
+
+  context 'CTE implementation' do
+    before do
+      stub_feature_flags(clusters_cte: true)
+    end
+
+    include_examples '#deployment_platform'
+  end
 end