* `RelationDef` & `RelationBuilder` are `Send` & `Sync` * [issues] add tests Co-authored-by: Chris Tsang <chris.2y3@outlook.com>
* `RelationDef` & `RelationBuilder` are `Send` & `Sync` * [issues] add tests Co-authored-by: Chris Tsang <chris.2y3@outlook.com>