check for recursion in references

src/grung/db.py

@@ -75,6 +75,8 @@ class RecordTable(table.Table):
         for field in document._metadata.fields.values():
             if isinstance(field.default, Iterable) and ref in document[field.name]:
                 raise CircularReferenceError(ref, field)
+            elif document[field.name] == ref:
+                raise CircularReferenceError(ref, field)
 
     def _check_unique(self, document) -> bool:
         matches = []