Add a method to retrieve projects when selective sync is enabled

This method allow us to enable selective sync support for the
FDW queries.

ee/app/models/geo/fdw/geo_node.rb

@@ -14,6 +14,18 @@ module Geo
       has_many :geo_node_namespace_links, class_name: 'Geo::Fdw::GeoNodeNamespaceLink'
       has_many :namespaces, class_name: 'Geo::Fdw::Namespace', through: :geo_node_namespace_links
 
+      def projects
+        return Geo::Fdw::Project.all unless selective_sync?
+
+        if selective_sync_by_namespaces?
+          projects_for_selected_namespaces
+        elsif selective_sync_by_shards?
+          projects_for_selected_shards
+        else
+          Geo::Fdw::Project.none
+        end
+      end
+
       def project_registries
         return Geo::ProjectRegistry.all unless selective_sync?
 
@@ -28,11 +40,25 @@ module Geo
 
       private
 
+      def projects_for_selected_namespaces
+        Geo::Fdw::Project
+          .within_namespaces(selected_namespaces_and_descendants.select(:id))
+      end
+
+      def projects_for_selected_shards
+        Geo::Fdw::Project.within_shards(selective_sync_shards)
+      end
+
       def registries_for_selected_namespaces
         Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder.new
           .within_namespaces(selected_namespaces_and_descendants.select(:id))
       end
 
+      def registries_for_selected_shards
+        Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder.new
+          .within_shards(selective_sync_shards)
+      end
+
       def selected_namespaces_and_descendants
         relation = selected_namespaces_and_descendants_cte.apply_to(Geo::Fdw::Namespace.all)
         relation.extend(Gitlab::Database::ReadOnlyRelation)
@@ -56,11 +82,6 @@ module Geo
         cte
       end
 
-      def registries_for_selected_shards
-        Gitlab::Geo::Fdw::ProjectRegistryQueryBuilder.new
-          .within_shards(selective_sync_shards)
-      end
-
       def fdw_namespaces_table
         Geo::Fdw::Namespace.arel_table
       end

ee/spec/models/geo/fdw/geo_node_spec.rb

@@ -8,6 +8,46 @@ RSpec.describe Geo::Fdw::GeoNode, :geo, type: :model do
     it { is_expected.to have_many(:namespaces).class_name('Geo::Fdw::Namespace').through(:geo_node_namespace_links) }
   end
 
+  # Disable transactions via :delete method because a foreign table
+  # can't see changes inside a transaction of a different connection.
+  describe '#projects', :delete do
+    before do
+      skip('FDW is not configured') unless Gitlab::Geo::Fdw.enabled?
+    end
+
+    let(:node) { create(:geo_node) }
+    let(:group_1) { create(:group) }
+    let(:group_2) { create(:group) }
+    let(:nested_group_1) { create(:group, parent: group_1) }
+    let(:project_1) { create(:project, group: group_1) }
+    let(:project_2) { create(:project, group: nested_group_1) }
+    let(:project_3) { create(:project, :broken_storage, group: group_2) }
+
+    subject { described_class.find(node.id) }
+
+    it 'returns all registries without selective sync' do
+      expect(subject.projects).to match_ids(project_1, project_2, project_3)
+    end
+
+    it 'returns projects that belong to the namespaces with selective sync by namespace' do
+      node.update!(selective_sync_type: 'namespaces', namespaces: [group_1])
+
+      expect(subject.projects).to match_ids(project_1, project_2)
+    end
+
+    it 'returns projects that belong to the shards with selective sync by shard' do
+      node.update!(selective_sync_type: 'shards', selective_sync_shards: %w[broken])
+
+      expect(subject.projects).to match_ids(project_3)
+    end
+
+    it 'returns nothing if an unrecognised selective sync type is used' do
+      node.update_attribute(:selective_sync_type, 'unknown')
+
+      expect(subject.projects).to be_empty
+    end
+  end
+
   # Disable transactions via :delete method because a foreign table
   # can't see changes inside a transaction of a different connection.
   describe '#project_registries', :delete do
@@ -33,15 +73,15 @@ RSpec.describe Geo::Fdw::GeoNode, :geo, type: :model do
     end
 
     it 'returns registries where projects belong to the namespaces with selective sync by namespace' do
-      node.update!(selective_sync_type: 'namespaces', namespaces: [group_1, nested_group_1])
+      node.update!(selective_sync_type: 'namespaces', namespaces: [group_1])
 
       expect(subject.project_registries).to match_array([registry_1, registry_2])
     end
 
     it 'returns registries where projects belong to the shards with selective sync by shard' do
-      node.update!(selective_sync_type: 'shards', selective_sync_shards: %w[default bar])
+      node.update!(selective_sync_type: 'shards', selective_sync_shards: %w[broken])
 
-      expect(subject.project_registries).to match_array([registry_1, registry_2])
+      expect(subject.project_registries).to match_array([registry_3])
     end
 
     it 'returns nothing if an unrecognised selective sync type is used' do