Raise when two validators conflict

Two @validates decorators that make use of the same name
is not supported.  Raise an exception.

Change-Id: Ia3e89ffdc9ef345a0de258e2ac0ac5e0bd421c61
Fixes: #3776

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index b76a6f727..e8aa08541 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1204,6 +1204,11 @@ class Mapper(InspectionAttr):
                 elif hasattr(method, '__sa_validators__'):
                     validation_opts = method.__sa_validation_opts__
                     for name in method.__sa_validators__:
+                        if name in self.validators:
+                            raise sa_exc.InvalidRequestError(
+                                "A validation function for mapped "
+                                "attribute %r on mapper %s already exists." %
+                                (name, self))
                         self.validators = self.validators.union(
                             {name: (method, validation_opts)}
                         )