How to limit choices of ForeignKey choices for Django raw_id_field

The method below works for me but it is a queryset that affects every admin that needs to use the Customer model. But if you have another Admin, e.g. Invoice that requires a different queryset, you might want to experiment a bit with model proxy.

Model

class Customer(models.Model):
    name = models.CharField(max_length=100)
    is_active = models.BooleanField()

class Order(models.Model):
    cust = models.ForeignKey(Customer)

Admin

class CustomerAdmin(admin.ModelAdmin):         
    def queryset(self, request):
        qs = super(CustomerAdmin, self).queryset(request)           
        return qs.filter(is_active=1)

class OrderAdmin():     
    raw_id_fields = ('cust', )    

I find the given solution (customizing the ModelAdmin queryset) a bit too restrictive, for realistic projects.

What I do, is usually the following:

• create a custom filter in my ModelAdmin (e.g. subclassing admin.SimpleListFilter, see the doc)

• create my subclass of widget ForeignKeyRawIdWidget as follows:

  class CustomRawIdWidget(ForeignKeyRawIdWidget):
  
      def url_parameters(self):
          """
          activate one or more filters by default
          """
  
          res = super(CustomRawIdWidget, self).url_parameters()
  
          res["<filter_name>__exact"] = "<filter_value>"
  
          return res
  

  note that what the only thing the custom widget does is to "preselect" the filter that, in turn, is responsible for "restricting" the queryset

• use the custom widget:

  class MyForm(forms.ModelForm):
  
      myfield = forms.ModelChoiceField(queryset=MyModel.objects.all(),
          ...
          widget=CustomRawIdWidget(
               MyRelationModel._meta.get_field('myfield').rel,
               admin.site))
  

One weak point of this approach is that the filter selected by the widget does not prevent from selecting some other instance from that model. If this is desired, I override the method ModelAdmin.save_model(...) (see the doc) to check that the related instances are only the allowed ones.

I find this approach a bit more complex, but much more flexible than limiting the queryset for the entire ModelAdmin.

I use similar to FSp approach in my Django 1.8 / Python 3.4 project:

from django.contrib import admin
from django.contrib.admin import widgets
from django.contrib.admin.sites import site
from django import forms

class BlogRawIdWidget(widgets.ForeignKeyRawIdWidget):
    def url_parameters(self):
        res = super().url_parameters()
        res['type__exact'] = 'PROJ'
        return res

class ProjectAdminForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['blog'].queryset = Blog.objects.filter(type='PROJ')
        self.fields['blog'].widget = BlogRawIdWidget(rel=Project._meta.get_field('blog').remote_field, admin_site=site)

    class Meta:
        # Django 1.8 convenience:
        fields = '__all__'
        model = Project

class ProjectAdmin(admin.ModelAdmin):
    form = ProjectAdminForm
    raw_id_fields = ('blog',)

to select only blog.type == 'PROJ' as foreign key Project.blog in django.admin. Because end-users may and will to select anything, unfortunately.

If you need to filter your raw_id list_view popup based on model instance you can use example below:

1. Write custom widget

class RawIdWidget(widgets.ForeignKeyRawIdWidget):

    def url_parameters(self):
        res = super(RawIdWidget, self).url_parameters()
        object = self.attrs.get('object', None)
        if object:
            # Filter variants by product_id
            res['product_id'] = object.variant.product_id
        return res

2. Pass instance on form init

class ModelForm(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        super(ModelForm, self).__init__(*args, **kwargs)
        obj = kwargs.get('instance', None)
        if obj and obj.pk is not None:
            self.fields['variant'].widget = RawIdWidget(
                rel=obj._meta.get_field('variant').rel,
                admin_site=admin.site,
                # Pass the object to attrs
                attrs={'object': obj}
            )