Option to Error with Default on New Field

[chukkwagon]

When adding a column to an existing table with a default value, django will lock the table while performing the update. Django best practices are to create a new column with null=True and no default value.

Reference:

Stack Overflow Summary

Django Docs

Can you add an option to lint for this best practice. Deploying to a production server with a default value set has a high probability of resulting in downtime.

[atodorov]

@chukkwagon how do we know a column has been newly added ?

pylint_django can probably run this sort of check only against fields which are inside a migration module/class and I have no idea how accurate that may or may not be. In all other cases I don't think the code would make a difference between an existing field and a newly added one.

Note: We can easily make a plugin for that (with or without the migrations specifics) but I'm definitely not in favor of teaching pylint_django recognize whether or not a column has been added beyond a couple of if statements.

@colinhowe what do you think? Any ideas?

[chukkwagon]

@atodorov exactly, I was thinking it would need to lint migration files. The pattern for a new field with a default would be that the migration file would contain the following (generalized) operation:

migrations.AddField(
    ..., 
    field=<any_field_name>(default=<any_default>)
)

[chukkwagon]

wow thanks for getting to this @atodorov !