Use _subscriptions join table to count upstream/downstream projects

Prior to this change we were joining through `upstream_subscriptions`
and `downstream_subscriptions` relations to count `upstream_projects`
and `downstream_projects`. This uses the `ci_subscriptions_projects`
table. Since we've added `disable_joins` to these
`has_many ... through: ...` relations these queries will now be less
efficient. So instead we've simplified the query to not join at all as
the `ci_subscriptions_projects.upstream_project_id` and
`ci_subscriptions_projects.downstream_project_id` are already both
`NOT NULL` foreign keys which means we already know for sure that
counting the `ci_subscriptions_projects` rows is equivalent to counting
the `projects` rows.

ee/app/models/ee/ci/pipeline.rb

@@ -191,7 +191,7 @@ module EE
 
       def project_has_subscriptions?
         project.feature_available?(:ci_project_subscriptions) &&
-          project.downstream_projects.any?
+          project.downstream_project_subscriptions.any?
       end
 
       def merge_train_ref?

ee/app/models/ee/project.rb

@@ -794,6 +794,14 @@ module EE
       available_features[feature]
     end
 
+    def upstream_projects_count
+      upstream_project_subscriptions.count
+    end
+
+    def downstream_projects_count
+      downstream_project_subscriptions.count
+    end
+
     def merge_pipelines_enabled?
       return false unless ci_cd_settings
 

ee/app/views/projects/settings/subscriptions/_index.html.haml

@@ -13,7 +13,7 @@
     %h5
       = _("Subscriptions")
       %span.badge.badge-pill
-        = @project.upstream_projects.count + @project.downstream_projects.count
+        = @project.upstream_projects_count + @project.downstream_projects_count
 
     %table.table.gl-mt-3
       %thead

ee/spec/models/project_spec.rb

@@ -3006,6 +3006,18 @@ RSpec.describe Project do
     end
   end
 
+  describe '#upstream_projects_count' do
+    it 'returns the upstream projects count' do
+      primary_project = create(:project, :public)
+      upstream_projects = create_list(:project, 2, :public)
+      primary_project.upstream_projects = upstream_projects
+
+      with_cross_joins_prevented do
+        expect(primary_project.upstream_projects_count).to eq(2)
+      end
+    end
+  end
+
   describe '#downstream_projects' do
     it 'returns the downstream projects' do
       primary_project = create(:project, :public)
@@ -3018,6 +3030,18 @@ RSpec.describe Project do
     end
   end
 
+  describe '#downstream_projects_count' do
+    it 'returns the downstream projects count' do
+      primary_project = create(:project, :public)
+      downstream_projects = create_list(:project, 2, :public)
+      primary_project.downstream_projects = downstream_projects
+
+      with_cross_joins_prevented do
+        expect(primary_project.downstream_projects_count).to eq(2)
+      end
+    end
+  end
+
   describe '#vulnerability_report_rule' do
     subject { project.vulnerability_report_rule }