Better support for exceptions / error messages in custom admin actions

[Danilo Bargen]

The docs don't mention any way to create error messages in custom admin actions. According to ​an answer on Stackoverflow, this can be achieved with:

from django.contrib import messages

# Then, when you need to error the user:
messages.error(request, "The message")

There are three issues with this:

• There's a message_user method on a ModelAdmin, but no similar thing for errors. This seems inconsistent.
• It's not mentioned in the docs. Errors in actions need to be handled.
• The error message isn't rendered with red background color, as it should be. A possible fix is described ​here.

[Travis Swicegood]

Thanks. Definitely something we should add. Probably something along the lines of adding a level kwarg to message_user.

[thiderman]

I'll tackle this one as part of my work at the Django sprint in Stockholm!

[thiderman]

Added pull request: ​https://github.com/django/django/pull/529

[Preston Holmes]

Allowing a string for the level for convenience seems fine - but we should still accept messages.INFO style constants.

I've made that change and added some more docs and release note here:

​https://github.com/ptone/django/compare/72bac6e8e12bd28cedb6874810812fcd3d137133…4b4f7c5dbf795b3db379e2100936bba06c71c718

Thanks for your work on this

[thiderman]

Looks good. Thanks for the improvements as well!

[Preston Holmes <preston@…>]

In edf7ad36faab8d45aafe1f96feaf46794de22fc1:

Fixed #18658 -- Improved ModelAdmin.message_user API

Thanks to Lowe Thiderman for the patch and tests

[Preston Holmes <preston@…>]

In 3a0e0230f76131cf23c0fdd0b18f3dd718c0f62f:

[1.5.x] Fixed #18658 -- Improved ModelAdmin.message_user API

Thanks to Lowe Thiderman for the patch and tests