python - 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)