Filtering two different model fields

[pljspahn]

I am modeling products (plants in my case) that have a foreign key relationship to a genus model.

class Product(models.Model):
    sku = models.CharField('SKU', max_length=14)
    name = models.CharField('Name', max_length=32)
    price = models.DecimalField('Price', max_digits=8, decimal_places=2)
    qoh = models.IntegerField('Quantity on Hand', default=0)
    genus = models.ForeignKey(Genus, on_delete=models.SET_NULL, null=True, blank=True)
    
    class Meta:
        ordering = ['sku']

    def __str__(self):
        return self.name

class Genus(models.Model):
    #ie Apple
    common = models.CharField('Common Genus', max_length=100)
    #ie Malus
    latin = models.CharField('Latin Genus', max_length=100)

    class Meta:
        ordering = ['common']
        verbose_name_plural = 'genera'

    def __str__(self):
        return self.common

I have a ModelMultipleChoiceFilter set up to filter by common genus. This works just like I'd expect.

class ProductFilter(django_filters.FilterSet):
    genus__common = django_filters.ModelMultipleChoiceFilter(queryset=Genus.objects.all(), label='Genus')
    class Meta:
        model = Product
        fields = ['genus__common']

I added a second filter to allow filtering by Latin name:

class LatinFilter(django_filters.FilterSet):
    genus__latin = django_filters.ModelMultipleChoiceFilter(queryset=Genus.objects.all(), label='Latin Genus')
    class Meta:
        model = Product
        fields = ['genus__latin']

This is used in my template like:

<form id="filters" method="GET">
    {{filter.form}}
    {{latin_filter.form}}
    <input type="submit">
</form>

This approach doesn't work as:

1. The form uses __str__ method of the Genus model to display the common genus instead of the Latin genus
2. It just doesn't filter correctly, returning all objects
3. Optionally, I'd like to change the ordering for LatinFilter so that they order by latin instead of common.

Where am I going wrong here?

[rpkilby]

The form uses __str__ method of the Genus model to display the common genus instead of the Latin genus

By default, choice labels are generated using __str__. To change this, you'll need to implement label_from_instance as described at the very bottom of the ModelChoiceField docs. Then, you'll need to provide the field_class to your ModelMultipleChoiceFilter.

It just doesn't filter correctly, returning all objects

This will still depend on your view, but I can at least say that you don't need to have two separate filterset classes. genus__common and genus__latin can be members of the same filterset.

Optionally, I'd like to change the ordering for LatinFilter so that they order by latin instead of common.

You've provide the queryset to the filter, so you tack on an .order_by() call there.

[pljspahn]

Thanks so much. I guess I was not fully understanding how __ works and thought there was some extra magic happening there that wasn't.

I changed my ProductFilter to the following and added LatinChoiceField and LatinFilter:

class LatinChoiceField(ModelMultipleChoiceField):
    def label_from_instance(self, obj):
        return obj.latin

class LatinFilter(django_filters.ModelMultipleChoiceFilter):
    field_class = LatinChoiceField

class ProductFilter(django_filters.FilterSet):
    genus__common = django_filters.ModelMultipleChoiceFilter(queryset=Genus.objects.all(), label='Genus')
    genus__latin = LatinFilter(queryset=Genus.objects.all().order_by('latin'), label='Latin', field_name='genus')
    class Meta:
        model = Product
        fields = ['genus__common', 'genus__latin']

I still don't really understand why the genus__latin Filter doesn't work unless I add field_name='genus' - that just doesn't make sense to me since I would expect the value to be field_name='genus__latin', but for whatever reason it does work.