Show applied datetime in showmigrations

[Timothy Schilling]

My idea is to add the applied datetime value to the showmigrations command.

I've run into the case where I'm working on a branch that involves a number of migrations across various apps, but then have to switch to a different branch which has different migrations. It can be troublesome to determine which migrations are new and need to be rolled back. I've recently started looking at the django_migrations table sorted on the applied column to determine which I've run recently. This would make switching between branches involving conflicting migrations easier.

There was some brief discussion ​here.

I've initially implemented this so that it would only apply to the --list option with a --verbosity of 2 and above. ​Here's what I have so far. I wasn't sure how to handle backporting.

​PR

Edited to strikeout old PR and reference the one to origin.

[Tim Graham]

We're past the feature freeze for 2.2, so please target the patch for 3.0 and send the pull request to django/django rather than to your fork.

[Ryan Siemens]

Whoops, didn't realize the link was a PR to a fork and not to origin!

[Carlton Gibson]

Just needs a squash and a rebase.

[Tim Graham <timograham@…>]

In 371ddade:

Refs #30186 -- Changed MigrationRecorder.applied_migrations() to return a dict.

[Tim Graham <timograham@…>]

In 7c68cea:

Fixed #30186 -- Made showmigrations --list display the applied datetimes at verbosity 2+.