Django: how to change the parameters of an external filter key by setting Django_Admin

Question

I have three models: LineType, Service, DomainName, Record, they are related m2m or foreignkey to each other. here is the code:

class LineType(models.Model): linename = models.CharField(max_length=30,primary_key=True) def __unicode__(self): return self.linename class Service(models.Model): servicename = models.CharField(max_length=30,primary_key=True) price = models.DecimalField(max_digits=8, decimal_places=2) line = models.ManyToManyField(LineType) def __unicode__(self): return self.servicename class DomainName(models.Model): domainname = models.CharField(max_length=30,primary_key=True) user = models.ForeignKey(SiteProfile) service = models.ForeignKey(Service) def __str__(self): return self.domainname class Record(models.Model): TYPE_CHOICES = ( ('A','A'), ('CNAME','CNAME'), ('MX','MX'), ) domainname = models.ForeignKey(DomainName) def get_line(self): domain = DomainName.objects.get(pk=self.domainname_id) service = Service.objects.get(pk=domain.service_id) lines = service.line.all() choices = [] for x in lines: choices.append((x.linename,x.linename)) return choices host = models.CharField(max_length=30) type = models.CharField(max_length=5,choices=TYPE_CHOICES,default='A') line = models.ForeignKey(LineType) destaddress = models.CharField(max_length=30) 

Let me introduce a model. Each domain name can have only one Service that other DomainNames can have. Each domain name has several entries. The service defines LineTypes that can be applied to the record.

I use Django admin to manage these models, but selecting the “row” in the record is all LineType objects. So the question is how to filter the LineType entries according to the “service” of this parent (DomainName).

Answer 1

Depending on your exact requirement and your version of Django, the answer can either set the limit_choices_to attribute of the foreign key , or configure the ModelAdmin form:

Using limit_choices_to

Just limit the selection of strings to those matching linename == 'foo'

 class Record(models.Model): # ... line = models.ForeignKey(LineType, limit_choices_to={'linename': 'foo'})) 

Using custom form

If an instance exists with an instance, we can select it as a set of query options

 class RecordAdminForm(forms.ModelForm): def __init__(self, *args, **kwargs): super(RecordAdminForm, self).__init__(*args, **kwargs) # access object through self.instance... if self.instance: valid_lines = self.instance.domainname.service.line.objects.all() self.fields['line'].queryset = valid_lines class RecordAdmin(admin.ModelAdmin): form = RecordAdminForm # ... 

Reference SO questions:

• how to limit foreignkey dropdown menu with restrictions?

• How to filter ForeignKey options in Django ModelForm?