IncompleteSelect Widgets with filter_by parameter only preselects partial set of initial values

[codematsing]

Hi Jacob,

I’ve been investigating this issue on my end, but I’m currently blocked on identifying where the solution should be applied.

Setup

states = forms.ModelMultipleChoice(
    initial=[2, 47],
    widget=SelectizeMultiple
)

counties = forms.ModelMultipleChoice(
    initial=[...],  # 10 items
    widget=DualSelector(filter_by={"state": "state_id"})
)

Expectation

• The DualSelector should pre-populate all 10 initial values.

Actual Behavior

• The DualSelector only captures a subset of the initial values.

Findings and observations

• IF DualSelector does NOT use the filter_by parameter, the expected behavior occurs.
• Issue only occurs when filter_by is set, and basis of filter also has initial values
• When a form widget inherits from IncompleteSelectMixin, the queryset is sliced to [:max_prefetch_choices]; consequently,
• The views.IncompleteSelectResponseMixin is responsible for dynamically updating the available options for a select field but will always display max_length=max_prefetch_choices.
• From browser dev tools, I observed that during the initial load, a network request is triggered:

http://localhost:8000/bootstrap/states?offset=0&filter-states=2&filter-states=47&field=__default__.counties

In my opinion, an improvement should be done on views.IncompleteSelectResponseMixin to choices=qs[:max_prefetch] + <field's initial values>, atleast on initial load?

Replication

• See replication here
• Go to: http://localhost:8000/bootstrap/states
• Note: I made max_prefetch_choices=5 to simplify test case and capture the case that's happening even when max_prefetch_choices is significantly higher (i.e. 250/default)
• Expected: 5 AK, 5 VA preselected values on page load. Similar to below. Instead, this occurs when counties form field does not have a "filter_by" parameter

• Actual: Only values in AK are pre-selected.

Any guidance would be appreciated.

[jrief]

I can confirm this problem. Unfortunately there is no simple solution to solve this. Filtering is done exclusively on the server through a fetch-request, but that request doesn't know the initial values.

I can fix this problem, if the initial values must not be filtered by the client. This means that the developer takes care while creating the list of initialized values, so that they match the filter.

I used your example and added value 2777 “Zapata (TX)” to the initial-list. Then “Zapata (TX)” would also show up in the right listbox, although the chosen filters state otherwise.

[jrief]

Please try with this fix and report if that would work for you.

[codematsing]

I'll review how I fixed this and see if I could provide a generic solution. Will send a PR over the weekend for your review 🙂