Fixed problem introduced with #refs 13711.

django/db/backends/__init__.py

@@ -520,6 +520,10 @@ class BaseDatabaseFeatures(object):
     # at the end of each save operation?
     supports_forward_references = True
 
+    # Does the backend uses proper method like 'truncate_name'
+    # to auto-truncate column names?
+    truncates_name = False
+
     # Is there a REAL datatype in addition to floats/doubles?
     has_real_datatype = False
     supports_subqueries_in_group_by = True

django/db/backends/oracle/base.py

@@ -107,6 +107,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_bitwise_or = False
     can_defer_constraint_checks = True
     supports_partially_nullable_unique_constraints = False
+    truncates_name = True
     has_bulk_insert = True
     supports_tablespaces = True
     supports_sequence_reset = False

django/db/models/base.py

@@ -1469,7 +1469,7 @@ class Model(six.with_metaclass(ModelBase)):
                 continue
             connection = connections[db]
             max_name_length = connection.ops.max_name_length()
-            if max_name_length is None:
+            if max_name_length is None or connection.features.truncates_name:
                 continue
             else:
                 if allowed_len is None:

tests/invalid_models_tests/test_models.py

@@ -18,7 +18,7 @@ def get_max_column_name_length():
     for db in settings.DATABASES.keys():
         connection = connections[db]
         max_name_length = connection.ops.max_name_length()
-        if max_name_length is None:
+        if max_name_length is None or connection.features.truncates_name:
             continue
         else:
             if allowed_len is None: