fix: fix performance issue loading latest version for pacticipant

lib/pact_broker/domain/pacticipant.rb

@@ -1,14 +1,44 @@
 require "pact_broker/db"
 require "pact_broker/messages"
 require "pact_broker/repositories/helpers"
-require "pact_broker/versions/latest_version"
 require "pact_broker/domain/label"
 require "pact_broker/string_refinements"
 require "pact_broker/pacticipants/generate_display_name"
 
 module PactBroker
   module Domain
+    class LatestVersionForPacticipantEagerLoader
+      def self.call(eo, **_other)
+        populate_associations(eo[:rows])
+      end
+
+      def self.populate_associations(pacticipants)
+        pacticipants.each { | pacticipant | pacticipant.associations[:latest_version] = nil }
+        pacticipant_ids = pacticipants.collect(&:id)
+
+        max_orders = PactBroker::Domain::Version
+                      .where(pacticipant_id: pacticipant_ids)
+                      .select_group(:pacticipant_id)
+                      .select_append { max(order).as(latest_order) }
+
+        max_orders_join = {
+          Sequel[:max_orders][:latest_order] => Sequel[:versions][:order],
+          Sequel[:max_orders][:pacticipant_id] => Sequel[:versions][:pacticipant_id]
+        }
+
+        latest_versions = PactBroker::Domain::Version
+                            .select_all_qualified
+                            .join(max_orders, max_orders_join, { table_alias: :max_orders})
+
+        latest_versions.each do | version |
+          pacticipant = pacticipants.find{ | pacticipant | pacticipant.id == version.pacticipant_id }
+          pacticipant.associations[:latest_version] = version
+        end
+      end
+    end
+
     class Pacticipant < Sequel::Model
+
       include Messages
       include PactBroker::Pacticipants::GenerateDisplayName
       using PactBroker::StringRefinements
@@ -21,7 +51,11 @@ class Pacticipant < Sequel::Model
       one_to_many :versions, :order => :order, :reciprocal => :pacticipant
       one_to_many :labels, :order => :name, :reciprocal => :pacticipant
       one_to_many :pacts
-      one_to_one :latest_version, :class => "PactBroker::Versions::LatestVersion", primary_key: :id, key: :pacticipant_id
+      one_to_one :latest_version, :class => "PactBroker::Domain::Version",
+        primary_key: :id, key: :pacticipant_id,
+        dataset: lambda { PactBroker::Domain::Version.where(pacticipant_id: id).order(Sequel.desc(:order)).limit(1) },
+        eager_loader: LatestVersionForPacticipantEagerLoader
+
       one_to_many :branch_heads, class: "PactBroker::Versions::BranchHead", primary_key: :id, key: :pacticipant_id
       one_to_many :branches, class: "PactBroker::Versions::Branch", primary_key: :id, key: :pacticipant_id
 

spec/lib/pact_broker/domain/pacticipant_spec.rb

@@ -0,0 +1,32 @@
+require "pact_broker/domain/pacticipant"
+
+module PactBroker
+  module Domain
+    describe Pacticipant do
+      describe "#latest_version" do
+        before do
+          td.create_consumer("Foo")
+            .create_consumer_version("1")
+            .create_consumer_version("2")
+            .create_consumer_version("3")
+            .create_consumer("Bar")
+            .create_consumer_version("10")
+            .create_consumer_version("11")
+            .create_consumer_version("12")
+        end
+
+        it "lazy loads" do
+          pacticipants = Pacticipant.order(:id).all
+          expect(pacticipants.first.latest_version.number).to eq "3"
+          expect(pacticipants.last.latest_version.number).to eq "12"
+        end
+
+        it "eager_loads" do
+          pacticipants = Pacticipant.order(:id).eager(:latest_version).all
+          expect(pacticipants.first.associations[:latest_version].number).to eq "3"
+          expect(pacticipants.last.associations[:latest_version].number).to eq "12"
+        end
+      end
+    end
+  end
+end