Fixes #366: Filter form and filterset support for boolean, select, and multiselect fields

[bctiemann]

Summary

Closes #366.

• BooleanFieldType: get_filterform_field() returns a NullBooleanField with a yes/no Select widget
• SelectFieldType: get_filterform_field() returns a DynamicMultipleChoiceField backed by the choice set API URL, enabling multi-value selection
• MultiSelectFieldType: Same as select — DynamicMultipleChoiceField backed by the choice set API
• get_filterset_class(): Adds explicit MultipleChoiceFilter for select fields (OR/field__in semantics) and a custom OR-of-__contains filter for multiselect ArrayField columns, replacing the inadequate auto-generated CharFilter(exact)

Test plan

• BooleanFieldFilterFormFieldTestCase — form field is NullBooleanField, not required, Select widget, choices include true/false
• BooleanFieldFiltersetTestCase — ?active=true narrows to True-only rows; ?active=false to False-only; no param returns all
• SelectFieldFilterFormFieldTestCase — form field is DynamicMultipleChoiceField, not required
• SelectFieldFiltersetTestCase — single value exact match; multiple values OR; no param returns all
• MultiSelectFieldFilterFormFieldTestCase — form field is DynamicMultipleChoiceField, not required
• MultiSelectFieldFiltersetTestCase — array containment match; OR union across multiple values; no duplicates; no param returns all

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[bctiemann]

@claude /review

[claude]

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PR Review: Filter form and filterset support for boolean, select, and multiselect fields

• Read changed files
• Review field_types.py changes
• Review filtersets.py changes
• Review test coverage
• Post review feedback

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Overview

This PR correctly implements get_filterform_field() for BooleanFieldType, SelectFieldType, and MultiSelectFieldType, and adds explicit MultipleChoiceFilter registrations in get_filterset_class() for select/multiselect fields to replace the inadequate auto-generated CharFilter(exact). Test coverage is comprehensive and well-organized. The logic is sound overall, with a few things worth noting.

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Issues / Observations

1. Boolean filterset relies entirely on auto-generated django-filters behavior

get_filterset_class() adds explicit filters for TYPE_SELECT and TYPE_MULTISELECT (lines 107–137), but does nothing for TYPE_BOOLEAN. The tests in BooleanFieldFiltersetTestCase pass {"active": "true"} and {"active": "false"} as strings, which works today only because django-filters auto-generates a BooleanFilter for BooleanField(null=True) — and that filter's underlying NullBooleanField.to_python() handles the string values.

This implicit reliance is fragile. A future django-filters version bump or change to the Meta.filter_overrides dict could silently break boolean filtering with no obvious cause. Adding an explicit filter, consistent with the select/multiselect approach, would make the intent clear:

# in get_filterset_class() alongside the select/multiselect block
elif co_field.type == CustomFieldTypeChoices.TYPE_BOOLEAN:
    attrs[co_field.name] = django_filters.BooleanFilter(field_name=co_field.name)

2. Identical implementations in SelectFieldType and MultiSelectFieldType [field_types.py:354-416]

get_filterform_field() is copy-pasted identically between the two field types. A minimal refactor would be to push the shared logic to a base class or a helper, but this is a style nit and low priority.

3. No null-guard for co_field.choice_set in filtersets.py:112

choices = list(co_field.choice_set.choices)

If a TYPE_SELECT or TYPE_MULTISELECT field somehow lacks a choice_set (e.g., data migration artifact), this raises AttributeError during filterset class construction rather than at query time, making it hard to diagnose. A guard or a descriptive error would help:

if co_field.choice_set is None:
    continue
choices = list(co_field.choice_set.choices)

4. filter_overrides for ArrayField is now partially redundant [filtersets.py:48-54]

The Meta.filter_overrides dict still maps ArrayField → CharFilter(icontains). For multiselect fields with explicit MultipleChoiceFilter registered, the explicit filter wins. But the override still applies to any hypothetical future ArrayField that isn't a multiselect — which is a non-issue today but could surprise someone reading the code. A comment noting the relationship would help.

5. Missing widget type assertion in select/multiselect form field tests

SelectFieldFilterFormFieldTestCase and MultiSelectFieldFilterFormFieldTestCase assert the field type and required=False, but don't verify the widget is APISelectMultiple. The boolean tests check widget type (test_form_field_widget_is_select); consistency here would be nice. [Low priority]

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Positives

• The make_multiselect_filter() factory correctly captures fname by value, avoiding the classic closure capture bug — good.
• Setting filter_multiselect.__name__ explicitly is required for django-filters method dispatch and is correctly done.
• Test data isolation via separate choice set names per test class (e.g., "SelectFFChoices366" vs "SelectFSChoices366") avoids cross-test pollution.
• test_filter_multiple_values_no_duplicates for multiselect is a thoughtful edge case that's easy to miss.
• The no_filter_returns_all tests correctly verify no unintended filtering occurs on empty params.

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Summary

The implementation is correct and the test coverage is solid. The main actionable item worth addressing before merge is item 1 (implicit boolean filter behavior) — it works today but is inconsistent with the explicit approach taken for select/multiselect and could silently regress. Items 2–5 are minor.

[bctiemann]

Item 1 is fixed.