Django admin inline: select_related

Question

Using Django 1.8 on Python 3.4.1 with models:

class Product(models.Model):
    name = models.CharField(max_length=255)
    # some more fields here

    def __str__(self):
        return self.name


class PricedProduct(models.Model):
    product = models.ForeignKey(Product, related_name='prices')
    # some more fields here

    def __str__(self):
        return str(self.product)

class Coming(models.Model):
    # some unimportant fields here


class ComingProducts(models.Model):
    coming = models.ForeignKey(Coming)
    priced_product = models.ForeignKey(PricedProduct)
    # more unimportant fields

and the following admin.py:

class ComingProductsInline(ForeignKeyCacheMixin, admin.TabularInline):
    model = ComingProducts


class ComingAdmin(admin.ModelAdmin):
    inlines = [ComingProductsInline]

Of course, i have a problem with multiply queries to database: i have a query for each item in list and a query for each line. So, having 100 items i get 100 ^ 2 queries. I've solved the problem with queries for each line with Caching queryset choices for ModelChoiceField or ModelMultipleChoiceField in a Django form But i still having problem with str method. I've tried the following:

1) adding prefetch_related to ComingAdmin:

def get_queryset(self, request):
    return super(ComingAdmin, self).get_queryset(request). \
    prefetch_related('products__product')

2) adding select_related to ComingProductInline:

def get_queryset(self, request):
    return super(ComingProductsInline, self).get_queryset(request). \
    select_related('priced_product__product')

3) Defining custom form for inline and adding select_related to field queryset:

 class ComingProductsInline(ForeignKeyCacheMixin, admin.TabularInline):
     model = ComingProducts
     form = ComingProductsAdminForm

 class ComingProductsAdminForm(ModelForm):
     def __init__(self, *args, **kwargs):
              super(ComingProductsAdminForm, self).__init__(args, kwargs)
              self.fields['priced_product'].queryset = PricedProduct.objects.all(). \
              select_related('product')

     class Meta:
         model = ComingProducts
         fields = '__all__'

4) Defining a custom formset:

 class ComingProductsInline(ForeignKeyCacheMixin, admin.TabularInline):
     model = ComingProducts
     formset = MyInlineFormset

 class MyInlineFormset(BaseInlineFormSet):
     def __init__(self, data=None, files=None, instance=None,
             save_as_new=False, prefix=None, queryset=None, **kwargs):
        super(MyInlineFormset, self).__init__(data, files, instance,
                                          save_as_new, prefix, queryset, **kwargs)
        self.queryset = ComingProducts.objects.all(). \
        prefetch_related('priced_product__product')

5) Different combinations for previous 4 methods

And nothing helps: each call of str for PricedProduct makes Django to perform a query for Product table. All of these methods were mentioned on stackoverflow, but they treated ModelAdmin, and do not help with Inline. What do i miss?

Answer 1

Inspired from @helpse answer you can also do the following if you just want to override the queryset for a single admin inline:

class ComingProductsInline(admin.TabularInline):
    model = ComingProducts

    def get_formset(self, request, obj=None, **kwargs):
        formset = super(ComingProductsInline, self).get_formset(request, obj, **kwargs)
        queryset = formset.form.base_fields["priced_product"].queryset
        queryset = queryset.select_related("product")
        formset.form.base_fields["priced_product"].queryset = queryset
        return formset

It might be sufficient for most of the cases.