Fix Elasticsearch sorting incorrectly from DB

Before this our search results were getting mixed up within a page. The
[`Records#records`](
https://github.com/elastic/elasticsearch-rails/blob/v6.1.0/elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb#L21
)
method is meant to sort again the query results based on the original
Elasticsearch ordering after loading from the DB, but this was not
working correctly in our code due to us monkey patching the
elasticsearch-model Gem and changing the value of
[`_id`](
https://gitlab.com/gitlab-org/gitlab/blob/8214da073b9692ffb75095390bc2fa5d862b5c05/ee/lib/gem_extensions/elasticsearch/model/response/records.rb#L9
)
for Elasticsearch records.

As such we needed to dig ourselves further into the monkey patch hole.
This MR replaces a single line inside `Records#records` method, which,
unfortunately, required us to replace the entire lengthy method.

https://gitlab.com/gitlab-org/gitlab/-/issues/229982

config/initializers/elastic_client_setup.rb

@@ -13,6 +13,7 @@ Gitlab.ee do
   Elasticsearch::Model::Adapter::Multiple::Records.prepend GemExtensions::Elasticsearch::Model::Adapter::Multiple::Records
   Elasticsearch::Model::Indexing::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Indexing::InstanceMethods
   Elasticsearch::Model::Adapter::ActiveRecord::Importing.prepend GemExtensions::Elasticsearch::Model::Adapter::ActiveRecord::Importing
+  Elasticsearch::Model::Adapter::ActiveRecord::Records.prepend GemExtensions::Elasticsearch::Model::Adapter::ActiveRecord::Records
   Elasticsearch::Model::Client::InstanceMethods.prepend GemExtensions::Elasticsearch::Model::Client
   Elasticsearch::Model::Client::ClassMethods.prepend GemExtensions::Elasticsearch::Model::Client
   Elasticsearch::Model::ClassMethods.prepend GemExtensions::Elasticsearch::Model::Client

ee/changelogs/unreleased/229982-fix-in-page-sort-order.yml

+---
+title: Fix Elasticsearch sorting incorrectly from DB
+merge_request: 37665
+author:
+type: fixed

ee/lib/gem_extensions/elasticsearch/model/adapter/active_record/records.rb

+# frozen_string_literal: true
+
+module GemExtensions
+  module Elasticsearch
+    module Model
+      module Adapter
+        module ActiveRecord
+          # rubocop:disable all
+          module Records
+            # Original method
+            # https://github.com/elastic/elasticsearch-rails/blob/v6.1.0/elasticsearch-model/lib/elasticsearch/model/adapters/active_record.rb#L21
+            def records
+              sql_records = klass.where(klass.primary_key => ids)
+              sql_records = sql_records.includes(self.options[:includes]) if self.options[:includes]
+
+              # Re-order records based on the order from Elasticsearch hits
+              # by redefining `to_a`, unless the user has called `order()`
+              #
+              sql_records.instance_exec(response.response['hits']['hits']) do |hits|
+                ar_records_method_name = :to_a
+                ar_records_method_name = :records if defined?(::ActiveRecord) && ::ActiveRecord::VERSION::MAJOR >= 5
+
+                define_singleton_method(ar_records_method_name) do
+                  if defined?(::ActiveRecord) && ::ActiveRecord::VERSION::MAJOR >= 4
+                    self.load
+                  else
+                    self.__send__(:exec_queries)
+                  end
+                  if !self.order_values.present?
+                    # BEGIN_MONKEY_PATCH
+                    #
+                    # Monkey patch sorting because we monkey patch ids and the
+                    # previous code uses `hit['_id']` which does not match our
+                    # record.id. We instead need `hit['_source']['id']`.
+                    @records.sort_by { |record| hits.index { |hit| hit['_source']['id'].to_s == record.id.to_s } }
+                    # END_MONKEY_PATCH
+                  else
+                    @records
+                  end
+                end if self
+              end
+
+              sql_records
+            end
+          end
+          # rubocop:enable all
+        end
+      end
+    end
+  end
+end

ee/spec/lib/gem_extensions/elasticsearch/model/adapter/active_record/records_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Elasticsearch::Model::Adapter::ActiveRecord::Records, :elastic do
+  describe '#records' do
+    let(:user) { create(:user) }
+    let(:search_options) { { options: { current_user: user, project_ids: :any } } }
+
+    before do
+      stub_ee_application_setting(elasticsearch_indexing: true)
+
+      @middle_relevant = create(
+        :issue,
+        title: 'Sorting could improve', # Some keywords in title
+        description: 'I think you could make it better'
+      )
+      @least_relevant = create(
+        :issue,
+        title: 'I love GitLab', # No keywords in title
+        description: 'There is so much to love! For example, you could not possibly make sorting any better'
+      )
+
+      @most_relevant = create(
+        :issue,
+        title: 'Make sorting better', # All keywords in title
+        description: 'This issue is here to make the sorting better'
+      )
+
+      ensure_elasticsearch_index!
+    end
+
+    it 'returns results in the same sorted order as they come back from Elasticsearch' do
+      expect(Issue.elastic_search('make sorting better', search_options).records.to_a).to eq([
+        @most_relevant,
+        @middle_relevant,
+        @least_relevant
+      ])
+    end
+  end
+end