Declarative mechanism for Django model rows

[Alex Dehnert]

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
things.

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

Thanks,
Alex

P.S. I previously asked this on StackOverflow at
https://stackoverflow.com/questions/70204467/declarative-mechanism-for-django-model-rows,
but I'm realising this list is probably better.

[Thomas Lockhart]

I may be completely misunderstanding your use case, but just in case…

You can have different views in your application, and if you don’t want to expose the data as separate pages then you might consider django-rest-framework to provide data in various ways, including across models. You’ll end up doing a bit of javascript but not have to dive back into your database for changes in how you want things to be accessed.

Flexible searches on attributes might be best supported by folding in ElasticSearch or something similar. It might seem like a heavy addition to a small-ish application, but once it it running it is flexible and trouble-free.

hth

- Tom

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[Ryan Nowakowski]

Check out fixtures:

https://docs.djangoproject.com/en/3.2/howto/initial-data/

[Carsten Fuchs]

Hello,

Am 08.12.21 um 20:25 schrieb Alex Dehnert:

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

If I understand your question correctly, you have a model that you always query like:

plans = Plan.objects.all()

and that is changed so infrequently that `plans` could be a read-only global, updated only on the rare ocassions it is changed in Admin (or shell etc.)? This would require to properly encapsulate the writes to the global, about which I too (if this covers your question) would be interested in getting help.

Best regards,
Carsten