ENH: add get_code function for TransactionErrors caused by container

src/caosdb/exceptions.py

@@ -257,6 +257,7 @@ class TransactionError(CaosDBException):
             self.entities instead.
 
         """
+
         if self.container is not None:
             return self.container
         from caosdb import Container
@@ -289,6 +290,18 @@ class TransactionError(CaosDBException):
                 "This TransActionError was caused by more than one EntityError."
             )
 
+    def get_code(self):
+        """In the special case of a container with at least one error message
+        with an integer code, return that code. Return None
+        otherwise.
+
+        """
+
+        if self.container is not None and self.container.get_errors() is not None:
+            for err in self.container.get_errors():
+                if err.code is not None:
+                    return err.code
+
     def _repr_reasons(self, indent):
         if self.get_errors() is not None and len(self.get_errors()) > 0:
             ret = "\n" + indent + "    +--| REASONS |--"