Chaining KeyTransform with 'contains' lookup uses builtin lookup instead of overridden lookup

[Sage Abdullah]

The previous implementation of django.contrib.postgres.fields.JSONField, when chained with a KeyTransform and a contains lookup, uses the overridden contains lookup that is JSON-based and not the builtin one that is pattern-based.

Using the example model in the 3.1 release notes,

class ContactInfo(models.Model):
    data = models.JSONField()

obj = ContactInfo.objects.create(data={
    'name': 'John',
    'cities': ['London', 'Cambridge'],
    'pets': {'dogs': ['Rufus', 'Meg']},
})
ContactInfo.objects.filter(
    data__cities__contains='Cambridge',
)

The query returns a queryset with obj in it, which is expected.

However, the following query:

ContactInfo.objects.filter(
    data__cities__contains='bridge',
)

Also returns a queryset with obj in it. Using the previous implementation, obj doesn't match the query because contains uses JSON-based containment checking. That is, it checks whether the array in data__cities contains an element that's exactly "bridge".