Manifests: introduce join function

Author: gmelikov

genesis_core/elements/dm/models.py

@@ -542,6 +542,7 @@ class Resource(
         "get_uri",
         "to_str",
         "index",
+        "join",
     ]
 
     element = relationships.relationship(
@@ -603,6 +604,11 @@ def index(self, field: str, idx: tp.Union[str, int] = 0) -> tp.Optional[str]:
         except (TypeError, IndexError):
             return None
 
+    def join(self, field: str, separator: str = ",") -> str:
+        if not self.actual_resource or not self.actual_resource.value:
+            return ""
+        return separator.join(self.actual_resource.value[field])
+
     def get_parameter_value(self, parameter: str):
         parts = parameter.split(":")
         resource_name = parts[0][1:]