Added is_relation property for convenience

src/schematools/types.py

@@ -1082,7 +1082,7 @@ def additional_relations(self) -> list[AdditionalRelationSchema]:
 
     def get_reverse_relation(self, field: DatasetFieldSchema) -> AdditionalRelationSchema | None:
         """Find the description of a reverse relation for a field."""
-        if not field.relation and not field.nm_relation:
+        if not field.is_relation:
             raise ValueError("Field is not a relation")
 
         for relation in self.additional_relations:
@@ -1473,6 +1473,13 @@ def is_internal(self) -> bool:
         """Id fields for table with composite key is only for internal (Django) use."""
         return self.is_primary and self._parent_table.has_composite_key
 
+    @cached_property
+    def is_relation(self) -> bool:
+        """Tell whether the field is a relation.
+        This is a convenience for ``bool(field.relation or field.nm_relation)``.
+        """
+        return bool(self.get("relation"))
+
     @cached_property
     def relation(self) -> str | None:
         """Give the 1:N relation, if it exists."""