Documented auto_now usage with bulk_update_with_history

[twolfson]

Description

When using bulk_update_with_history, a DateTimeField using auto_now doesn't automatically update like it does with Model.save()

This PR documents the issue under "Common Issues" and offers a convention-based solution

Related Issue

#1054

Motivation and Context

The motivation is to spread awareness of the issue and guide people towards a solution. It seems like a rather quiet bug that can really hurt data accuracy.

How Has This Been Tested?

The code is excerpts from our code

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have run the pre-commit run command to format and lint.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have added my name and/or github handle to AUTHORS.rst
• I have added my change to CHANGES.rst
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #1055 (dd38fb0) into master (6d09c3e) will not change coverage.
The diff coverage is n/a.

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  Lines        1231     1231           
  Branches      199      199           
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  Hits         1197     1197           
  Misses         16       16           
  Partials       18       18           

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[rossmechanic]

@twolfson what's the point? Don't you already have those auto_now dates on the history objects? I've traditionally ignored updated/created columns from my base model in my historical model

[twolfson]

I think there's 2 ways to interpret your response so I'll respond to both:

• Why do you need an updated_at column on your normal model? (this is the fix I'm proposing to document)
  • This is a great question!
  • It's not used in application code so much, but it's very useful to avoid looking at extra pages or doing complex joins when looking into issues
• Why does the historical model need an updated_at column?
  • It doesn't but this issue isn't about that. It's about the first one -- when using bulk_update_with_history, we want to automatically update the auto_now column on the normal model
  • Arguably this isn't django-simple-history responsibility, but that's why it's only being proposed as documentation, not as a code-based solution