django.db.utils.NotSupportedError when attempting to change max_length on CharField

Using Django Using the ORM
1

I have the following field:

    name_combined = models.CharField(
        max_length=600,
        editable=False,
    )

which is a field that combines two Charfields on save. I have found that 600 is too small. As I have taken over the project it is in production - so cannot simply rollback migrations to zero and start again.

Changing the max_length or the field to a text field results in the following error:

django.db.utils.NotSupportedError: cannot alter type of a column used by a view or rule
DETAIL:  rule _RETURN on view v_viewing_report depends on column "name_combined"

it is a Postgres database. What do rules and views mean in this context and how do you go about changing the max_length or field type to allow for the change?

2

Still interested by the meaning of “view” or “rules” in the Postgres context, but have decided to truncate the characters to 600 when creating ‘name_combined’.

It is a niche case which was only found with the use of model bakery, and will rarely be required to be more than 600 characters anyway.

3

For a general overview of what a database view is, a web search will yield many sources of definitions and information. (Cue the obligatory wikipedia link: View (SQL) - Wikipedia).

PostgreSQL’s docs cover the specifics of their implementation starting at PostgreSQL: Documentation: 14: 3.2. Views. Also see PostgreSQL: Documentation: 14: Chapter 41. The Rule System

To directly answer your initial question - how do you modify a column that is also part of a view, you need to drop and re-create the view.