Disable signal when running the remove_farm_perms migration

[hoangpn]

Promgen has a signal that creates Audit Logs every time a user removes the permission of another user. This is not necessary in the case where we run a migration script to clean up permission objects because they are automatically deleted by Promgen itself. This signal can even cause some unexpected errors if it is triggered in this case. Therefore, we temporarily disable this signal when running the migration script.

[vincent-olivert-riera]

@hoangpn ,

This signal can even cause some unexpected errors if it is triggered in this case.

Please provide more details about that. Under which circumstances it happens, and which error message do you see?

I would like a more detailed explanation.

[vincent-olivert-riera]

@hoangpn ,

This signal can even cause some unexpected errors if it is triggered in this case.

Please provide more details about that. Under which circumstances it happens, and which error message do you see?

After our private discussion between me and @hoangpn , we have decided that we will go with this commit message:

Disconnect signal while running the remove_farm_perms migration

At this moment, the real relationship between a Project and a Farm is one-to-one. To honor that, in
a future PR we plan to define the relationship between Project and Farm as a OneToOneField [1]. When
that happens, the project_id field on the Farm model will not exist anymore.

If the remove_farm_perms migration runs with that new code in place, the delete_log signal that is
triggered when the permissions are removed from a Farm instance will fail because at some point (in
order to construct a log) will try to access the project_id field of that Farm instance.

Taking into account that we do not care about Farm permissions anymore (because they will be
inherited from the Project to which it belongs), we also do not care about those logs.

Therefore, to allow that migration to run without any issues in the future, we are disconnecting the
offending signal while it runs.

1: https://docs.djangoproject.com/en/5.2/topics/db/examples/one_to_one/#one-to-one-relationships

[hoangpn]

@hoangpn ,

This signal can even cause some unexpected errors if it is triggered in this case.

Please provide more details about that. Under which circumstances it happens, and which error message do you see?

The error message is django.db.utils.OperationalError: (1054, "Unknown column 'promgen_farm.project_id' in 'field list'")
This happend when I tried add a new OneToOneField named "project" to the Farm model. (I was preparing for the future changes about Farm-Project relationship). Here is how the error happened:

1. When the 0033_remove_farm_perms migration script was ran, it removed the unneccesary permissions related to the Farm.
2. Currently, we are recording the deletion of the permissions and saving message to the database. We are also using the str() method of the deleted object to build the logging message.
3. We are deleting the Django-Guardian's UserObjectPermission model. The str() method of this model was trying to access to the related object of the permission to get more information, which was the Farm model.
4. The OneToOneField "project" was added after the No. 0033 migration script. Therefore, Django ORM saw the different between the model in source code and the table in the database at the moment the script was ran, so it throw the exception "Unknown column..."

You can see that this error occurs indirectly. It cannot represent the entire reason I skipped the signal in this PR. However, I found that this signal is unnecessary when running the migration script, and skipping it also helps us fix the bug in a simple way, so I decided to skip it.