ENH: Introduce bad query errors

src/caosdb/exceptions.py

@@ -141,6 +141,19 @@ class ResourceNotFoundException(ClientErrorException):
         ClientErrorException.__init__(self, msg=msg, status=404, body=None)
 
 
+# ######################### Bad query errors ###########################
+
+class BadQueryError(CaosDBException):
+    """Base class for query errors that are not transaction errors."""
+
+
+class QueryNotUniqueError(BadQueryError):
+    """A unique query or retrieve found more than one entity."""
+
+
+class EmptyUniqueQueryError(BadQueryError):
+    """A unique query or retrieve dound no result."""
+
 # ######################### Transaction errors #########################