1 files changed, 39 insertions, 0 deletions
diff --git a/lib/gitlab/background_migration/copy_column.rb b/lib/gitlab/background_migration/copy_column.rb
new file mode 100644
index 00000000000..a2cb215c230
--- /dev/null
+++ b/lib/gitlab/background_migration/copy_column.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # CopyColumn is a simple (reusable) background migration that can be used to
+    # update the value of a column based on the value of another column in the
+    # same table.
+    #
+    # For this background migration to work the table that is migrated _has_ to
+    # have an `id` column as the primary key.
+    class CopyColumn
+      # table - The name of the table that contains the columns.
+      # copy_from - The column containing the data to copy.
+      # copy_to - The column to copy the data to.
+      # start_id - The start ID of the range of rows to update.
+      # end_id - The end ID of the range of rows to update.
+      def perform(table, copy_from, copy_to, start_id, end_id)
+        return unless connection.column_exists?(table, copy_to)
+
+        quoted_table = connection.quote_table_name(table)
+        quoted_copy_from = connection.quote_column_name(copy_from)
+        quoted_copy_to = connection.quote_column_name(copy_to)
+
+        # We're using raw SQL here since this job may be frequently executed. As
+        # a result dynamically defining models would lead to many unnecessary
+        # schema information queries.
+        connection.execute <<-SQL.strip_heredoc
+        UPDATE #{quoted_table}
+        SET #{quoted_copy_to} = #{quoted_copy_from}
+        WHERE id BETWEEN #{start_id} AND #{end_id}
+        SQL
+      end
+
+      def connection
+        ActiveRecord::Base.connection
+      end
+    end
+  end
+end