How to Handle Non Nullable and Default Value

Related Error

You are trying to add a non-nullable field '...'
to choice without a default; we can't do that
(the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py
Select an option:

Explanations

• (blog post) What do you do when 'makemigrations' is telling you About your Lack of Default Value
• (video) You are trying to add a non-nullable field ' ' to ' ' without a default; we can't do that

Solutions

Key to Icons

• ☑ Tested.
• ⚠ May be dangerous.

For cmsplugin_ptr

1. ☑ Select option 1), then see:
   • Follow-Up Error
   • Notes ▸ cmsplugin_ptr

For Other Fields

1. ⚠ Select option 1) and hope for the best.
2. ☑ Select option 2) and provide a sensible default (not None a.k.a. null).
3. ⚠ (blog post) (hack) Add A Migration For A Non-Null Foreignkey Field In Django

Follow-Up Error

If you permit Null to be a default, then you may have this new error:

django.db.utils.IntegrityError: column "..." contains null values

Solutions

1. delete relevant migration files and rebuild migrations
2. delete all migration files and rebuild migrations

Notes

cmsplugin_ptr

If the field is cmsplugin_ptr then know that

• it is a database relationship field managed automatically by Django,
• you may see it in workarounds for other plugins (source a, source b),
• you should not add or overwrite it unless you know what you are doing.

W. Bomar learned everything in the intitial version of this document after trying to overwrite cmsplugin_ptr while extending its model from source a. His solution was delete all migration files and rebuild migrations.

Appendix

• Django CMS ▸ How to create Plugins ▸ Handling Relations
• [BUG] Plugins with models that don't directly inherit from CMSPlugin or an abstract model cannot be copied