ENH: add is_reference to db.Property

https://gitlab.com/caosdb/caosdb-pylib/-/merge_requests/63

src/caosdb/common/models.py

@@ -31,6 +31,7 @@ from __future__ import print_function, unicode_literals
 import re
 import sys
 from builtins import str
+from copy import deepcopy
 from functools import cmp_to_key
 from hashlib import sha512
 from os import listdir
@@ -1504,6 +1505,42 @@ class Property(Entity):
 
         return super(Property, self).to_xml(xml, add_properties)
 
+    def is_reference(self, server_retrieval=False):
+        """Returns whether this Property is a reference
+
+        Parameters
+        ----------
+        server_retrieval : bool, optional
+            If True and the datatype is not set, the Property is retrieved from the server, by default False
+
+        Returns
+        -------
+        bool, NoneType
+            Returns whether this Property is a reference or None if a server call is needed to
+            check correctly, but server_retrieval is set to False.
+
+        """
+
+        if self.datatype is None:
+
+            if not self.is_valid():
+                # this is a workaround to prevent side effects
+                # since retrieve currently changes the object
+
+                if server_retrieval:
+                    tmp_prop = deepcopy(self)
+                    tmp_prop.retrieve()
+
+                    return tmp_prop.is_reference()
+                else:
+                    return None
+            else:
+                # a valid property without datatype has to be an RT
+
+                return True
+        else:
+            return is_reference(self.datatype)
+
 
 class Message(object):