Apply reviewer feedback

- Setup associations
- Minor stylistics changes

app/graphql/resolvers/project_merge_requests_resolver.rb

@@ -28,14 +28,15 @@ module Resolvers
       argument_names.delete(:merged_before)
       argument_names.delete(:merged_after)
 
+      # no extra filtering arguments are provided
+      return unless argument_names.empty?
+      return unless args[:merged_after] || args[:merged_before]
+
       # Detecting a specific query pattern:
       # mergeRequests(mergedAfter: "X", mergedBefore: "Y") {
       #   count
       # }
-      lookahead.selects?(:count) &&
-        lookahead.selections.size == 1 && # no other nodes are selected
-        (args[:merged_after] || args[:merged_before]) &&
-        argument_names.empty? # no extra filtering arguments are provided
+      lookahead.selects?(:count) && lookahead.selections.size == 1 # no other nodes are selected
     end
   end
 end

app/models/merge_request/metrics.rb

@@ -5,7 +5,7 @@ class MergeRequest::Metrics < ApplicationRecord
   belongs_to :pipeline, class_name: 'Ci::Pipeline', foreign_key: :pipeline_id
   belongs_to :latest_closed_by, class_name: 'User'
   belongs_to :merged_by, class_name: 'User'
-  belongs_to :target_project, class_name: 'Project'
+  belongs_to :target_project, class_name: 'Project', inverse_of: :merge_requests
 
   before_save :ensure_target_project_id
 

app/models/project.rb

@@ -218,6 +218,7 @@ class Project < ApplicationRecord
 
   # Merge Requests for target project should be removed with it
   has_many :merge_requests, foreign_key: 'target_project_id', inverse_of: :target_project
+  has_many :merge_request_metrics, foreign_key: 'target_project', class_name: 'MergeRequest::Metrics', inverse_of: :target_project
   has_many :source_of_merge_requests, foreign_key: 'source_project_id', class_name: 'MergeRequest'
   has_many :issues
   has_many :labels, class_name: 'ProjectLabel'

config/feature_flags/development/optimized_merge_request_count_with_merged_at_filter.yml

@@ -2,7 +2,7 @@
 name: optimized_merge_request_count_with_merged_at_filter
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/52113
 rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/299347
-milestone: '13.8'
+milestone: '13.9'
 type: development
 group: group::optimize
 default_enabled: false

spec/finders/merge_request/metrics_finder_spec.rb

@@ -6,13 +6,13 @@ RSpec.describe MergeRequest::MetricsFinder do
   let_it_be(:current_user) { create(:user) }
   let_it_be(:project) { create(:project, :repository) }
   let_it_be(:merge_request_not_merged) { create(:merge_request, :unique_branches, source_project: project) }
+  let_it_be(:merged_at) { Time.new(2020, 5, 1) }
   let_it_be(:merge_request_merged) do
     create(:merge_request, :unique_branches, :merged, source_project: project).tap do |mr|
-      mr.metrics.update!(merged_at: Time.new(2020, 5, 1))
+      mr.metrics.update!(merged_at: merged_at)
     end
   end
 
-  let(:merged_at) { merge_request_merged.metrics.merged_at }
   let(:params) do
     {
       target_project: project,

spec/lib/gitlab/import_export/all_models.yml

@@ -561,6 +561,7 @@ project:
 - exported_protected_branches
 - incident_management_oncall_schedules
 - debian_distributions
+- merge_request_metrics
 award_emoji:
 - awardable
 - user
@@ -589,6 +590,7 @@ lfs_file_locks:
 project_badges:
 - project
 metrics:
+- target_project
 - merge_request
 - latest_closed_by
 - merged_by

spec/models/merge_request/metrics_spec.rb

@@ -5,6 +5,7 @@ require 'spec_helper'
 RSpec.describe MergeRequest::Metrics do
   describe 'associations' do
     it { is_expected.to belong_to(:merge_request) }
+    it { is_expected.to belong_to(:target_project) }
     it { is_expected.to belong_to(:latest_closed_by).class_name('User') }
     it { is_expected.to belong_to(:merged_by).class_name('User') }
   end
@@ -36,5 +37,15 @@ RSpec.describe MergeRequest::Metrics do
         is_expected.not_to include([metrics_2])
       end
     end
+
+    describe '.by_target_project' do
+      let(:target_project) { metrics_1.target_project }
+
+      subject { described_class.by_target_project(target_project) }
+
+      it 'finds metrics record with the associated target project' do
+        is_expected.to eq([metrics_1])
+      end
+    end
   end
 end

spec/models/project_spec.rb

@@ -21,6 +21,7 @@ RSpec.describe Project, factory_default: :keep do
     it { is_expected.to have_many(:services) }
     it { is_expected.to have_many(:events) }
     it { is_expected.to have_many(:merge_requests) }
+    it { is_expected.to have_many(:merge_request_metrics) }
     it { is_expected.to have_many(:issues) }
     it { is_expected.to have_many(:milestones) }
     it { is_expected.to have_many(:iterations) }