filter foreignkey field in django admin

Question

I have these models:

class Entity(models.Model):
       name=models.CharField(max_length=100)
      
class Theme(models.Model):
   name=models.CharField(max_length=100)
   entity=models.OneToOneField(Entity)

class Company(models.Model):
    name=models.CharField(max_length=100)
    theme=models.OneToOneField(Theme,null=True,blank=True)

I want to filter the theme field when adding a Company in the admin, something like this:

class CompanyAdmin(admin.ModelAdmin):
   def queryset(self, request):
      qs = super(CompanyAdmin, self).queryset(request)
      qs.theme.queryset = Theme.objects.filter(name__iexact='company')
      return qs
      
admin.site.register(Company, CompanyAdmin)

I've tried many things, but nothing worked! How can I do this?

Answer 1

Use the render_change_form method:

class CompanyAdmin(admin.ModelAdmin):
    def render_change_form(self, request, context, *args, **kwargs):
         context['adminform'].form.fields['theme'].queryset = Theme.objects.filter(name__iexact='company')
         return super(CompanyAdmin, self).render_change_form(request, context, *args, **kwargs)

Answer 2

I actually prefer to do it in get_form like so:

Django < 2:

class CompanyAdmin(admin.ModelAdmin):
    def get_form(self, request, obj=None, **kwargs):
        form = super(CompanyAdmin, self).get_form(request, obj, **kwargs)
        form.fields['theme'].queryset = Theme.objects.filter(name__iexact='company')
        return form

Django >= 2

class CompanyAdmin(admin.ModelAdmin):
    def get_form(self, request, obj=None, **kwargs):
        form = super(CompanyAdmin, self).get_form(request, obj, **kwargs)
        form.base_fields['theme'].queryset = Theme.objects.filter(name__iexact='company')
        return form

Answer 3

look here http://books.agiliq.com/projects/django-admin-cookbook/en/latest/filter_fk_dropdown.html

@admin.register(Hero)
class HeroAdmin(admin.ModelAdmin, ExportCsvMixin):
    ...
    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        if db_field.name == "category":
            kwargs["queryset"] = Category.objects.filter(name__in=['God', 'Demi God'])
        return super().formfield_for_foreignkey(db_field, request, **kwargs)

Answer 4

In Django 3 it is easy :

class CompanyAdmin(admin.ModelAdmin):
    list_display = ('name','theme')
    list_filter = ('theme__name',)

admin.site.register(Company,CompanyAdmin)

This will show you a filter on the right of your screen with the list of your theme's name.

Answer 5

Another option is to create a custom model form where the queryset attribute of the theme field will be fine tuned to meet your needs.

class CompanyForm(ModelForm):
    class Meta:
        model = CompanyForm
        fields = __all__ # or a tuple of fields

    def __init__(self, *args, **kwargs):
        super(CompanyForm, self).__init__(*args, **kwargs)
        if self.instance: # Editing and existing instance
            self.fields['theme'].queryset = Theme.objects.filter(name__iexact='company')

This model form can be also reused outside of the django admin area.