feat: RelationalBone add getDefaultValue

src/viur/core/bones/relational.py

@@ -1309,6 +1309,27 @@ def getUniquePropertyIndexValues(self, valuesCache: dict, name: str) -> list[str
         elif isinstance(value, list):
             return self._hashValueForUniquePropertyIndex([x["dest"]["key"] for x in value])
 
+    def getDefaultValue(self, skeletonInstance):
+        if callable(self.defaultValue):
+            key = self.defaultValue(skeletonInstance, self)
+        elif isinstance(self.defaultValue, list):
+            key = self.defaultValue
+        elif isinstance(self.defaultValue, dict):
+            return self.defaultValue.copy()
+        else:
+            key = self.defaultValue
+        if not key:
+            return None
+        if self.multiple:
+            if isinstance(key, list):
+                return [self.createRelSkelFromKey(k) for k in key]
+            else:
+                return [self.createRelSkelFromKey(key)]
+        else:
+            if isinstance(key, list):
+                key = key[0]
+            return self.createRelSkelFromKey(key)
+
     def structure(self) -> dict:
         return super().structure() | {
             "type": f"{self.type}.{self.kind}",