Validate queuing entry before we upsert it into database

This ensures that only valid objects can be upserted into the database.

app/models/ci/build.rb

@@ -37,7 +37,7 @@ module Ci
 
     has_one :deployment, as: :deployable, class_name: 'Deployment'
     has_one :pending_state, class_name: 'Ci::BuildPendingState', inverse_of: :build
-    has_one :queuing_entry, class_name: 'Ci::PendingBuild', foreign_key: :build_id
+    has_one :queuing_entry, class_name: 'Ci::PendingBuild', foreign_key: :build_id, inverse_of: :build
     has_many :trace_sections, class_name: 'Ci::BuildTraceSection'
     has_many :trace_chunks, class_name: 'Ci::BuildTraceChunk', foreign_key: :build_id, inverse_of: :build
     has_many :report_results, class_name: 'Ci::BuildReportResult', inverse_of: :build
@@ -1038,6 +1038,14 @@ module Ci
       options.dig(:allow_failure_criteria, :exit_codes).present?
     end
 
+    def all_queuing_entries
+      # We can have only one queuing entry, because there is a unique index on
+      # `build_id`, but we need a relation to remove this single queuing entry
+      # more efficiently in a single statement without actually load data.
+
+      ::Ci::PendingBuild.where(build_id: self.id)
+    end
+
     protected
 
     def run_status_commit_hooks!

app/models/ci/pending_build.rb

@@ -5,6 +5,14 @@ module Ci
     extend Gitlab::Ci::Model
 
     belongs_to :project
-    belongs_to :build, class_name: 'Ci::Build'
+    belongs_to :build, class_name: 'Ci::Build', inverse_of: :queuing_entry
+
+    def self.upsert!(build)
+      entry = self.new(build: build, project: build.project)
+
+      raise ArgumentError, 'queuing entry invalid' unless entry.valid?
+
+      upsert({ build_id: entry.build_id, project_id: entry.project_id })
+    end
   end
 end

app/services/ci/update_build_queue_service.rb

@@ -19,11 +19,9 @@ module Ci
       raise InvalidQueueTransition unless transition.to == 'pending'
 
       transition.within_transaction do
-        attributes = { build_id: build.id, project_id: build.project.id }
-
-        ::Ci::PendingBuild.upsert(attributes).then do |result|
-          raise ArgumentError if result.length > 1
+        result = ::Ci::PendingBuild.upsert!(build)
 
+        unless result.empty?
           metrics.increment_queue_operation(:build_queue_push)
 
           result.rows.dig(0, 0)
@@ -40,12 +38,12 @@ module Ci
       raise InvalidQueueTransition unless transition.from == 'pending'
 
       transition.within_transaction do
-        ::Ci::PendingBuild.where(build_id: build.id).delete_all.then do |removed| # rubocop:disable CodeReuse/ActiveRecord
+        removed = build.all_queuing_entries.delete_all
+
         if removed > 0
           metrics.increment_queue_operation(:build_queue_pop)
-          end
 
-          removed > 0
+          build.id
         end
       end
     end

spec/services/ci/update_build_queue_service_spec.rb

@@ -44,7 +44,7 @@ RSpec.describe Ci::UpdateBuildQueueService do
 
     context 'when duplicate entry exists' do
       before do
-        ::Ci::PendingBuild.create(build: build, project: project)
+        ::Ci::PendingBuild.create!(build: build, project: project)
       end
 
       it 'does nothing and returns updated build id' do
@@ -71,7 +71,7 @@ RSpec.describe Ci::UpdateBuildQueueService do
       it 'removes pending build in a transaction' do
         dequeued = subject.pop(build, transition)
 
-        expect(dequeued).to be true
+        expect(dequeued).to eq build.id
       end
 
       it 'increments queue pop metric' do
@@ -89,7 +89,7 @@ RSpec.describe Ci::UpdateBuildQueueService do
       it 'does nothing if there is no pending build to remove' do
         dequeued = subject.pop(build, transition)
 
-        expect(dequeued).to be false
+        expect(dequeued).to be_nil
       end
     end