Save extra query

Combine management project query in cluster hierarchy so that we save a
query in DeploymentPlatform.

app/models/clusters/clusters_hierarchy.rb

@@ -38,12 +38,25 @@ module Clusters
                      raise ArgumentError, "unknown type for #{clusterable}"
                    end
 
+      if clusterable.is_a?(::Project)
+        cte << management_clusters_query
+      end
+
       cte << base_query
       cte << parent_query(cte)
 
       cte
     end
 
+    # Management clusters should be first in the hierarchy so we use 0 for the
+    # depth column.
+    #
+    # group_parent_id is un-used but we still need to match the same number of
+    # columns as other queries in the CTE.
+    def management_clusters_query
+      clusterable.management_clusters.select([clusters_star, 'NULL AS group_parent_id', "0 AS #{DEPTH_COLUMN}"])
+    end
+
     def group_clusters_base_query
       group_parent_id_alias = alias_as_column(groups[:parent_id], 'group_parent_id')
       join_sources = ::Group.left_joins(:clusters).arel.join_sources

app/models/concerns/deployment_platform.rb

@@ -12,16 +12,10 @@ module DeploymentPlatform
   private
 
   def find_deployment_platform(environment)
-    find_management_cluster(environment) ||
     find_platform_kubernetes_with_cte(environment) ||
       find_instance_cluster_platform_kubernetes(environment: environment)
   end
 
-  # EE would override this and utilize environment argument
-  def find_management_cluster(_environment)
-    management_clusters.enabled.default_environment.first&.platform_kubernetes
-  end
-
   # EE would override this and utilize environment argument
   def find_platform_kubernetes_with_cte(_environment)
     Clusters::ClustersHierarchy.new(self).base_and_ancestors

ee/app/models/concerns/ee/deployment_platform.rb

@@ -4,14 +4,6 @@ module EE
   module DeploymentPlatform
     extend ::Gitlab::Utils::Override
 
-    override :find_management_cluster
-    def find_management_cluster(environment)
-      management_clusters
-        .enabled
-        .on_environment(environment, relevant_only: true)
-        .first&.platform_kubernetes
-    end
-
     override :find_platform_kubernetes_with_cte
     def find_platform_kubernetes_with_cte(environment)
       return super unless environment && feature_available?(:multiple_clusters)

spec/models/clusters/clusters_hierarchy_spec.rb

@@ -44,14 +44,40 @@ describe Clusters::ClustersHierarchy do
       end
     end
 
+    context 'cluster has management project' do
+      let!(:project_cluster) { create(:cluster, :project, projects: [project]) }
+      let!(:group_cluster) { create(:cluster, :group, groups: [group], management_project: management_project) }
+
+      let(:group) { create(:group) }
+      let(:project) { create(:project, group: group) }
+      let(:management_project) { create(:project) }
+
+      it 'returns clusters for management_project' do
+        expect(base_and_ancestors(management_project)).to eq([group_cluster])
+      end
+
+      it 'returns clusters for project' do
+        expect(base_and_ancestors(project)).to eq([project_cluster, group_cluster])
+      end
+
+      it 'returns clusters for group' do
+        expect(base_and_ancestors(group)).to eq([group_cluster])
+      end
+    end
+
     context 'project in nested group with clusters at some levels' do
-      let!(:child) { create(:cluster, :group, groups: [child_group]) }
+      let!(:child) { create(:cluster, :group, groups: [child_group], management_project: management_project) }
       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) }
+      let(:management_project) { create(:project) }
+
+      it 'returns clusters for management_project' do
+        expect(base_and_ancestors(management_project)).to eq([child])
+      end
 
       it 'returns clusters for project' do
         expect(base_and_ancestors(project)).to eq([child, ancestor])