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I have three models: LineType, Service, DomainName, Record, they have m2m or foreignkey relation between 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 the model. Each DomainName could only have one Service which other DomainNames can have. Each DomainName have multi Records. Service define LineTypes which can be applied to the Record.

I use Django admin to manage these models, but the choice of the "line" in Record are all the LineType object.So the question is how to filter the LineType of Record according to the "service" of it's parent(DomainName).

okm
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edylam
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1 Answers1

1

Depends on your exact requirement and your version of Django, the answer may either setting the limit_choices_to attribute of the foreign key, or customizing the ModelAdmin form:

Using limit_choices_to

Simply limit line choices to those matching linename == 'foo'

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

Using a custom form

If an instance exists when instantiating the form, we can select it's domain's service's lines as the queryset choices

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:

Community
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tutuDajuju
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