Support jsonb Default Value in add_column_with_default Migration Helper

changelogs/unreleased/support-jsonb-default-value.yml

+---
+title: Support jsonb default in add_column_with_default migration helper
+merge_request: 29871
+author:
+type: other

lib/gitlab/database/migration_helpers.rb

@@ -434,7 +434,8 @@ module Gitlab
           end
 
           begin
-            update_column_in_batches(table, column, default, &block)
+            default_after_type_cast = connection.type_cast(default, column_for(table, column))
+            update_column_in_batches(table, column, default_after_type_cast, &block)
 
             change_column_null(table, column, false) unless allow_null
           # We want to rescue _all_ exceptions here, even those that don't inherit

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -583,6 +583,24 @@ describe Gitlab::Database::MigrationHelpers do
           model.add_column_with_default(:projects, :foo, :integer, default: 10, limit: 8)
         end
       end
+
+      it 'adds a column with an array default value for a jsonb type' do
+        create(:project)
+        allow(model).to receive(:transaction_open?).and_return(false)
+        allow(model).to receive(:transaction).and_yield
+        expect(model).to receive(:update_column_in_batches).with(:projects, :foo, '[{"foo":"json"}]').and_call_original
+
+        model.add_column_with_default(:projects, :foo, :jsonb, default: [{ foo: "json" }])
+      end
+
+      it 'adds a column with an object default value for a jsonb type' do
+        create(:project)
+        allow(model).to receive(:transaction_open?).and_return(false)
+        allow(model).to receive(:transaction).and_yield
+        expect(model).to receive(:update_column_in_batches).with(:projects, :foo, '{"foo":"json"}').and_call_original
+
+        model.add_column_with_default(:projects, :foo, :jsonb, default: { foo: "json" })
+      end
     end
 
     context 'inside a transaction' do