Django model booleanfield only 1 True for table -

i have model

class owner(models.model):     name = models.charfield(max_length=10)  class phonenumber(models.model):     isactive = model.booleanfield(default=false)     owner = model.foreignkey('owner') 

i want enforce 1 phonenumber active if user, when creating or editing 'not active' phonenumber, accidentally sets 'active' , there 'active' phonenumber form should not submit , clear error displayed change 'active' field false , error text "please deactivate old active phonenumber before assigning new active phonenumber"

how do this? in validation method in class check ?

thank you

often validation can done automatically defining unique_together in model's meta class, here not work possibly have many inactive phone numbers each user. need custom validation. 1 way in clean method of model itself, called when form validated.

def clean(self):     if self.isactive:         active = phonenumber.objects.filter(isactive=true, owner=self.owner)         if self.pk:             active = active.exclude(pk=self.pk)         if active.exists():             raise validationerror("an active phone number exists user")