Fixed #27295 -- Added a system check to prohibit model names that start or end with an underscore or contain double underscores.

django/db/models/base.py

@@ -1265,7 +1265,11 @@ class Model(six.with_metaclass(ModelBase)):
             errors.extend(cls._check_fields(**kwargs))
             errors.extend(cls._check_m2m_through_same_relationship())
             errors.extend(cls._check_long_column_names())
-            clash_errors = cls._check_id_field() + cls._check_field_name_clashes()
+            clash_errors = (
+                cls._check_id_field() +
+                cls._check_field_name_clashes() +
+                cls._check_model_name_db_lookup_clashes()
+            )
             errors.extend(clash_errors)
             # If there are field name clashes, hide consequent column name
             # clashes.
@@ -1469,6 +1473,30 @@ class Model(six.with_metaclass(ModelBase)):
 
         return errors
 
+    @classmethod
+    def _check_model_name_db_lookup_clashes(cls):
+        errors = []
+        model_name = cls.__name__
+        if model_name.startswith('_') or model_name.endswith('_'):
+            errors.append(
+                checks.Error(
+                    "The model name '%s' cannot start or end with an underscore "
+                    "as it collides with the query lookup syntax." % model_name,
+                    obj=cls,
+                    id='models.E023'
+                )
+            )
+        elif LOOKUP_SEP in model_name:
+            errors.append(
+                checks.Error(
+                    "The model name '%s' cannot contain double underscores as "
+                    "it collides with the query lookup syntax." % model_name,
+                    obj=cls,
+                    id='models.E024'
+                )
+            )
+        return errors
+
     @classmethod
     def _check_index_together(cls):
         """ Check the value of "index_together" option. """