Initial migration fails if app name has upper-case letters on Oracle

[Carsten Fuchs]

In a Django project that was created pre-1.7, did not use South before and was recently upgraded to Django 1.7.4 and is otherwise fine, I was trying to convert it to use migrations, following the docs at ​https://docs.djangoproject.com/en/1.7/topics/migrations/#adding-migrations-to-apps

Creating the initial migrations with makemigrations went well, but the first run of migrate aborted with error "django.db.utils.DatabaseError: ORA-00955: name is already used by an existing object". Please see my post to django-users at ​https://groups.google.com/forum/#!topic/django-users/lVS24BGFouo for details.

Debugging this quickly brought me to MigrationExecutor.detect_soft_applied() in django/db/migrations/executor.py, whose lines 153 to 154 say:

                if model._meta.db_table not in self.connection.introspection.get_table_list(self.connection.cursor()):
                    return False

It seems that get_table_list() returns all lower-case list items, whereas model._meta.db_table was, in my case, "Lori_aub". Consequently, False was wrongly returned.

Adding lower(), i.e. changing this to

                if model._meta.db_table.lower() not in self.connection.introspection.get_table_list(self.connection.cursor()):
                    return False

entirely fixed the problem for me! :-)

(Sorry for not having a PR readily available.)

[Markus Holtermann]

Your fix will break on all other backends as they keep the table name as given (e.g. AppLabel_modelname). As far as I know Oracle converts table names to all uppercase internally. Since app_label is supposed to be all lower case and model_name = object_name.lower() the problem is with not explicitly making the app_label lower case.

This is the get_table_list() implementation in 1.7 for Oracle:

# django/db/backends/oracle/introspection.py
def get_table_list(self, cursor):
    cursor.execute("SELECT TABLE_NAME FROM USER_TABLES")
    return [row[0].lower() for row in cursor.fetchall()]

and for 1.8+

# django/db/backends/oracle/introspection.py
def get_table_list(self, cursor):
    cursor.execute("SELECT TABLE_NAME, 't' FROM USER_TABLES UNION ALL "
                   "SELECT VIEW_NAME, 'v' FROM USER_VIEWS")
    return [TableInfo(row[0].lower(), row[1]) for row in cursor.fetchall()]

[Shai Berger]

While it is different in symptoms and code-paths, this is essentially the same issue as #20487: The Oracle backend (not Oracle itself) converts names to uppercase on the way into the db, and so it must convert them back to lowercase on the way out -- which, in some cases, is not the correct transformation.

The right workaround for you is, of course, to fake the initial migration. I'm not closing this as a dupe (yet), because the migrations behavior deserves more careful study.

[Carsten Fuchs]

Ok, many thanks for your feedback! I was not aware that the scope of this issue is actually much broader...

(In hindsight, it is clear to me that faking the initial migration was the right workaround, but I deliberately did not use --fake because from a user's perspective, knowing little about the implementation details, I did not want to forgo any other issues it might have identified. I did not expect any, but it seemed like a good extra verification step.)

[Markus Holtermann]

FWIW this is also a bit related to #24337.

[Mariusz Felisiak]

Fixed in 530dd193f2a1c791c703f3f961e2296cbb316bf9.