Use data_source_exists? instead of table_exists?

Use data_source_exists? where possible instead of table_exists? in order to be Rails5 compatible

app/models/project.rb

@@ -68,7 +68,7 @@ class Project < ActiveRecord::Base
   add_authentication_token_field :runners_token
-  before_validation :mark_remote_mirrors_for_removal, if: -> { ActiveRecord::Base.connection.table_exists?(:remote_mirrors) }
+  before_validation :mark_remote_mirrors_for_removal, if: -> { RemoteMirror.table_exists? }
   before_save :ensure_runners_token

config/initializers/active_record_migration.rb

+require 'active_record/migration'
+
+module ActiveRecord
+  class Migration
+    # data_source_exists? is not available in 4.2.10, table_exists deprecated in 5.0
+    def table_exists?(table_name)
+      ActiveRecord::Base.connection.data_source_exists?(table_name)
+    end
+  end
+end

lib/gitlab/background_migration/prepare_untracked_uploads.rb

@@ -54,7 +54,8 @@ module Gitlab
       def ensure_temporary_tracking_table_exists
         table_name = :untracked_files_for_uploads
-        unless UntrackedFile.connection.table_exists?(table_name)
+
+        unless ActiveRecord::Base.connection.data_source_exists?(table_name)
           UntrackedFile.connection.create_table table_name do |t|
             t.string :path, limit: 600, null: false
             t.index :path, unique: true

lib/gitlab/database.rb

@@ -188,8 +188,11 @@ module Gitlab
     end
     def self.cached_table_exists?(table_name)
-      # Rails 5 uses data_source_exists? instead of table_exists?
-      connection.schema_cache.table_exists?(table_name)
+      if Gitlab.rails5?
+        connection.schema_cache.data_source_exists?(table_name)
+      else
+        connection.schema_cache.table_exists?(table_name)
+      end
     end
     private_class_method :connection

spec/lib/gitlab/background_migration/populate_untracked_uploads_spec.rb

@@ -114,7 +114,7 @@ describe Gitlab::BackgroundMigration::PopulateUntrackedUploads, :sidekiq, :migra
     it 'does not drop the temporary tracking table after processing the batch, if there are still untracked rows' do
       subject.perform(1, untracked_files_for_uploads.last.id - 1)
-      expect(ActiveRecord::Base.connection.table_exists?(:untracked_files_for_uploads)).to be_truthy
+      expect(ActiveRecord::Base.connection.data_source_exists?(:untracked_files_for_uploads)).to be_truthy
     end
     it 'drops the temporary tracking table after processing the batch, if there are no untracked rows left' do

spec/lib/gitlab/database_spec.rb

@@ -314,8 +314,13 @@ describe Gitlab::Database do
   describe '.cached_table_exists?' do
     it 'only retrieves data once per table' do
-      expect(ActiveRecord::Base.connection).to receive(:table_exists?).with(:projects).once.and_call_original
-      expect(ActiveRecord::Base.connection).to receive(:table_exists?).with(:bogus_table_name).once.and_call_original
+      if Gitlab.rails5?
+        expect(ActiveRecord::Base.connection).to receive(:data_source_exists?).with(:projects).once.and_call_original
+        expect(ActiveRecord::Base.connection).to receive(:data_source_exists?).with(:bogus_table_name).once.and_call_original
+      else
+        expect(ActiveRecord::Base.connection).to receive(:table_exists?).with(:projects).once.and_call_original
+        expect(ActiveRecord::Base.connection).to receive(:table_exists?).with(:bogus_table_name).once.and_call_original
+      end
       2.times do
         expect(described_class.cached_table_exists?(:projects)).to be_truthy

spec/support/helpers/migrations_helpers.rb

@@ -10,10 +10,6 @@ module MigrationsHelpers
     ActiveRecord::Migrator.migrations_paths
   end
-  def table_exists?(name)
-    ActiveRecord::Base.connection.table_exists?(name)
-  end
-
   def migrations
     ActiveRecord::Migrator.migrations(migrations_paths)
   end