Feature Request: New PostgreSQL ArrayField

[Liamine Cheridi]

Hello to all,

at Pricemoov we’re using Postgresql arrays (https://www.postgresql.org/docs/15/arrays.html) to store prices of a given product.

More precisely, a given product can have either:

        - standard: N prices (1d array)

        - calendar: D * N prices, when the client is setting up different prices for each day of a given time window (2d array)

So far, we modelled both use cases using a single table queried through raw SQL queries.

We’re currently trying to migrate the raw SQL queries to Django’s ORM, using ArrayField-s.

As per what is written at https://docs.djangoproject.com/en/4.1/ref/contrib/postgres/fields/#arrayfield, in a given field of a table, we can either have:

        - an ArrayField (1d), or

        - an ArrayField(base_field=ArrayField(…) …) (2d)

but cannot have both.

Instead of having different fields or different tables (one for standard and one for calendar use cases), we’re exploring the possibility of adding a custom field ArrayOrMatrixField. To have a better description of that idea, we pushed the PR https://github.com/django/django/pull/15943 (WIP, please do not consider it as a version ready to be reviewed for merge)

Given that such a field is not available in Django yet, we think there may be a reason for that. More precisely, we’d have the following questions:

        - do you anticipate any feature incompatibility/logical bomb that would be introduced by such a custom field?

        - if not, would you be interested in integrating such a field in Django?

Best regards,

Liamine Cheridi, Backend Engineer at Pricemoov

[Jacob Rief]

Hello Liamine,

Django offers a JSONField which can be used to store an array.

You can use it to store a list of prices. What's the benefit of using an array instead of JSON?

– Jacob

[Adrian Torres]

Hi Liamine,

I think there's various solutions you could try before going the custom field route:

* You could try just using the 2D version and use some sentinel value for the date (NULL?) to treat the case where you just want an array of N prices.

* You could try using django-polymorphic [1] which would allow you to define one "StandardPricingProduct" model and one "CalendarPricingProduct" model, and be able to query them together (e.g. get all products regardless of "type").

* You could try Jacob's suggestion.

* You could try creating a pricing model and have a FK between Pricing and Product -- I know you want to avoid this, but to me it sounds simpler and more maintainable than going the custom field route.

Cheers,

Adrian

[1] https://django-polymorphic.readthedocs.io/en/stable/

[Liamine Cheridi]

Hello, thanks a lot for your answers.
I am very embarrassed to say that I went a bit too fast in my testing of nested ArrayField, and it turns out that it actually fits my use case.
   def test_nested_array_accepts_1D_array(self):
    instance = NestedIntegerArrayModel(id=1, field=[1, 2, 3])
    instance.save()
    instance_from_db = NestedIntegerArrayModel.objects.get(id=1)
    self.assertEqual(instance_from_db.field, [1, 2, 3])


This test actually passes, sorry for the noise :S.

Best regards,
Liamine

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Cordialement,

Liamine Cheridi Backend Engineer 0630178896