feat: add index to verifications table to improve performance of 'lat…

…est verification' query

db/migrations/20210815_add_provider_version_id_index_to_verifications.rb

@@ -0,0 +1,7 @@
+Sequel.migration do
+  change do
+    alter_table(:verifications) do
+      add_index([:pact_version_id, :id], name: "verifications_pact_version_id_id_index")
+    end
+  end
+end

lib/pact_broker/pacts/pact_version.rb

@@ -1,6 +1,7 @@
 require "sequel"
 require "pact_broker/repositories/helpers"
 require "pact_broker/verifications/latest_verification_for_pact_version"
+require "pact_broker/verifications/latest_verification_id_for_pact_version_and_provider_version"
 
 module PactBroker
   module Pacts
@@ -17,7 +18,7 @@ class PactVersion < Sequel::Model(:pact_versions)
       one_to_one(:latest_verification,
         class: "PactBroker::Domain::Verification",
         read_only: true,
-        dataset: lambda { PactBroker::Domain::Verification.where(id: PactBroker::Domain::Verification.select(Sequel.function(:max, :id)).where(pact_version_id: id)) },
+        dataset: lambda { PactBroker::Domain::Verification.where(id: PactBroker::Verifications::LatestVerificationIdForPactVersionAndProviderVersion.select(Sequel.function(:max, :verification_id)).where(pact_version_id: id)) },
         key: :pact_version_id, primary_key: :id,
         eager_block: lambda { | ds | ds.latest_by_pact_version }
       )