Allow overriding the base queryset to be used in Snippets IndexView

[laymonage]

Part of wagtail/rfcs#85. Incorporates #10271.

This PR extracts a get_base_queryset() method to the generic IndexView (inspired by ModelAdmin's WMABaseView.get_base_queryset() for the initial logic of the queryset, before any filters or search are applied. The API is surfaced in SnippetViewSet as get_queryset(request) to mirror ModelAdmin.get_queryset(request) API. On the Snippets IndexView.get_base_queryset(), we first try to call SnippetViewSet.get_queryset(self.request). If the result is None (the default), the original implementation in the generic IndexView is used.

Please check the following:

• Do the tests still pass?¹
• Does the code comply with the style guide?
  • Run make lint from the Wagtail root.
• For Python changes: Have you added tests to cover the new/fixed behaviour?
• For new features: Has the documentation been updated accordingly?

Please describe additional details for testing this change.

Continuing the test example in #10256:

from wagtail.snippets.models import register_snippet
from wagtail.snippets.views.snippets import SnippetViewSet


class PersonViewSet(SnippetViewSet):
    icon = "user"
    list_per_page = 2
    chooser_per_page = 1
    admin_url_namespace = "some_namespace"
    base_url_path = "deep/within/the/admin"
    chooser_admin_url_namespace = "my_chooser_namespace"
    chooser_base_url_path = "choose/wisely"
    # this will generate exact filters
    list_filter = ["job_title", "first_name"]
    # alternatively, this will generate filters with lookups
    list_filter = {
        "job_title": ["contains"],
        "first_name": ["contains"],
        "first_published_at": ["date"],
    }

    def get_queryset(self, request):
        return self.model._default_manager.all().exclude(job_title__contains="[HIDDEN]")


register_snippet(Person, viewset=PersonViewSet)

If you create a Person object with a job title that contains [HIDDEN], it won't be shown on the listing view.

Footnotes

1. Development Testing ↩

[squash-labs]

Manage this branch in Squash

Test this branch here: https://laymonagecustom-snippets-get-q-egkin.squash.io

[gasman]

Looks good to me!

[gasman]

Not sure if this encompasses the search tests that now have to be done as a TransactionTestCase instead as of #10208 - will find out when I rebase... - but if it does, I think the work needed to untangle that might outweigh the benefit of pulling out these methods, in which case I might skip this commit.

[gasman]

Merged in fbd3cca