Wednesday, December 8, 2021

Declarative mechanism for Django model rows

With some frequency, I end up with models who contents are approximately
constant. Are there good ways of handling this?

For example, I might have a set of plans that users can sign up
for, with various attributes -- ID, name, order in the list of plans,
cost, whether the purchaser needs to be a student/FOSS project/etc.. I'm
going to rarely add/remove/change rows, and when I do there's likely going
to be code changes too (eg, to change landing pages), so I'd like the
contents of the model (not just the schema) to be managed in the code
rather than through the Django admin (and consequently use pull requests
to manage them, make sure test deploys are in sync, etc.). I'd also like
it to be in the database, though, so I can select them using any column of
the model, filter for things like "show me any project owned by a paid
account", etc..

I think my ideal would be something like "have a list of model instances
in my code, and either Django's ORM magically pretends they're actually in
the database, or makemigrations makes data migrations for me", but I don't
think that exists?

The two workable approaches that come to mind are to either write data
migrations by hand or use regular classes (or dicts) and write whatever
getters and filters I actually want by hand.

Data migrations give me all the Django ORM functionality I might want, but
any time I change a row I need to write a migration by hand, and figuring
out the actual state involves either looking in the Django admin or
looking through all the data migrations to figure out their combined
impact. (Oh, and if somebody accidentally deletes the objects in the
database (most likely on a test install...) or a migration is screwy
recovering will be a mess.)

Just using non-ORM classes in the source is a clearer, more declarative
approach, but I need to add replacements for many things I might normally
do in the ORM (.objects.get(...), __plan__is_student,
.values(plan__is_student).annotate(...), etc.).

Which of these approaches is better presumably depends on how much ORM
functionality I actually want and how often I expect to be changing

Are there other good approaches for this? Am I missing some Django feature
(or add-on) that makes this easier?


P.S. I previously asked this on StackOverflow at,
but I'm realising this list is probably better.

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