Django MySQL error when creating tables

Question

I am building a django app with a MySQL DB. When I run \'python manage.py migrate\' for the first time, some tables are created well then some errors appear. The error broug

Answer 1

I met this problem while I use:

$ python manage.py test

If you didn't make migrations for those models which has a field that is a Foreignkey to django.contrib.auth.models.User, it will cause that problem.

And if you enabled --keepdb you will find there is no auth_user table and some other django's admin table.

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Let's trace the whole problem:

run:

$ python manage.py test --verbosity=3

You can see the foreigngkey constraint exception raised after

Running deferred SQL...

the deferred sql is similar to

"ALTER TABLE xxx ADD CONSTRAINT xx FOREIGN KEY (x) REFERENCES auth_user"

check the source code of django/core/management/commands/migrate.py:

for statement in deferred_sql:
    cursor.execute(statement)

The defered_sql comes from manifest.items() for loop,

and manifest comes from all_models,

and all_models comes from the app_config.label in app_labels.

this is the argument passed by

self.sync_apps(connection, executor.loader.unmigrated_apps)

Therefore, executor.loader.unmigrated_apps will contain the unmigrated_app's label, and if you happend to has a Foreignkey to Django's auth_user, it will cause Foreignkey constrain Error cause at the time, there is no table named auth_user.

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solution:

suppose app is the module which contains those Foreignkey attributes class:

$ python manage.py migrate auth
$ python manage.py migrate
$ python manage.py makemigrations app

and, if you have other modules depend on the app, suppose the database tables have the same field with app module, you need:

$ python manage.py make migrate app --fake