1 files changed, 62 insertions, 0 deletions
diff --git a/lib/gitlab/database/migrations/swap_columns_default.rb b/lib/gitlab/database/migrations/swap_columns_default.rb
new file mode 100644
index 00000000000..0005c606b87
--- /dev/null
+++ b/lib/gitlab/database/migrations/swap_columns_default.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Migrations
+      class SwapColumnsDefault
+        delegate(
+          :change_column_default, :quote_table_name, :quote_column_name, :column_for,
+          to: :@migration_context
+        )
+
+        def initialize(migration_context:, table:, column1:, column2:)
+          @migration_context = migration_context
+          @table = table
+          @column_name1 = column1
+          @column_name2 = column2
+        end
+
+        def execute
+          default1 = find_default_by(@column_name1)
+          default2 = find_default_by(@column_name2)
+          return if default1 == default2
+
+          change_sequence_owner_if(default1[:sequence_name], @column_name2)
+          change_sequence_owner_if(default2[:sequence_name], @column_name1)
+
+          change_column_default(@table, @column_name1, default2[:default])
+          change_column_default(@table, @column_name2, default1[:default])
+        end
+
+        private
+
+        def change_sequence_owner_if(sequence_name, column_name)
+          return if sequence_name.blank?
+
+          @migration_context.execute(<<~SQL.squish)
+            ALTER SEQUENCE #{quote_table_name(sequence_name)}
+            OWNED BY #{quote_table_name(@table)}.#{quote_column_name(column_name)}
+          SQL
+        end
+
+        def find_default_by(name)
+          column = column_for(@table, name)
+          if column.default_function.present?
+            {
+              default: -> { column.default_function },
+              sequence_name: extract_sequence_name_from(column.default_function)
+            }
+          else
+            {
+              default: column.default
+            }
+          end
+        end
+
+        def extract_sequence_name_from(expression)
+          expression[/nextval\('([^']+)'/, 1]
+        end
+      end
+    end
+  end
+end