Ensure identity queries use lower query to match index

app/models/user.rb

@@ -430,6 +430,7 @@ class User < ApplicationRecord
   scope :by_id_and_login, ->(id, login) { where(id: id).where('username = LOWER(:login) OR email = LOWER(:login)', login: login) }
   scope :dormant, -> { active.where('last_activity_on <= ?', MINIMUM_INACTIVE_DAYS.day.ago.to_date) }
   scope :with_no_activity, -> { active.where(last_activity_on: nil) }
+  scope :by_provider_and_extern_uid, ->(provider, extern_uid) { joins(:identities).merge(Identity.with_extern_uid(provider, extern_uid)) }
 
   def preferred_language
     read_attribute('preferred_language') ||
@@ -554,10 +555,6 @@ class User < ApplicationRecord
       end
     end
 
-    def for_github_id(id)
-      joins(:identities).merge(Identity.with_extern_uid(:github, id))
-    end
-
     # Find a User by their primary email or any associated secondary email
     def find_by_any_email(email, confirmed: false)
       return unless email

lib/gitlab/bitbucket_import/importer.rb

@@ -63,10 +63,7 @@ module Gitlab
 
         return users[username] if users.key?(username)
 
-        users[username] = User.select(:id)
-                              .joins(:identities)
-                              .find_by("identities.extern_uid = ? AND identities.provider = 'bitbucket'", username)
-                              .try(:id)
+        users[username] = User.by_provider_and_extern_uid(:bitbucket, username).select(:id).first&.id
       end
       # rubocop: enable CodeReuse/ActiveRecord
 

lib/gitlab/github_import/user_finder.rb

@@ -138,7 +138,7 @@ module Gitlab
 
       # rubocop: disable CodeReuse/ActiveRecord
       def query_id_for_github_id(id)
-        User.for_github_id(id).pluck(:id).first
+        User.by_provider_and_extern_uid(:github, id).select(:id).first&.id
       end
       # rubocop: enable CodeReuse/ActiveRecord
 

lib/gitlab/gitlab_import/importer.rb

@@ -56,8 +56,8 @@ module Gitlab
 
       # rubocop: disable CodeReuse/ActiveRecord
       def gitlab_user_id(project, gitlab_id)
-        user = User.joins(:identities).find_by("identities.extern_uid = ? AND identities.provider = 'gitlab'", gitlab_id.to_s)
-        (user && user.id) || project.creator_id
+        user_id = User.by_provider_and_extern_uid(:gitlab, gitlab_id).select(:id).first&.id
+        user_id || project.creator_id
       end
       # rubocop: enable CodeReuse/ActiveRecord
     end

lib/gitlab/legacy_github_import/user_formatter.rb

@@ -35,12 +35,7 @@ module Gitlab
       def find_by_external_uid
         return unless id
 
-        identities = ::Identity.arel_table
-
-        User.select(:id)
-            .joins(:identities)
-            .find_by(identities[:provider].eq(:github).and(identities[:extern_uid].eq(id)))
-            .try(:id)
+        User.by_provider_and_extern_uid(:github, id).select(:id).first&.id
       end
       # rubocop: enable CodeReuse/ActiveRecord
     end

spec/models/user_spec.rb

@@ -5852,4 +5852,17 @@ RSpec.describe User do
       end
     end
   end
+
+  describe '.by_provider_and_extern_uid' do
+    it 'calls Identity model scope to ensure case-insensitive query', :aggregate_failures do
+      expected_user = create(:user)
+      create(:identity, extern_uid: 'some-other-name-id', provider: :github)
+      create(:identity, extern_uid: 'my_github_id', provider: :gitlab)
+      create(:identity)
+      create(:identity, user: expected_user, extern_uid: 'my_github_id', provider: :github)
+
+      expect(Identity).to receive(:with_extern_uid).and_call_original
+      expect(described_class.by_provider_and_extern_uid(:github, 'my_github_id')).to match_array([expected_user])
+    end
+  end
 end