如何在Django视图中使用unique_together方法

Question

class Model1(models.Model):
     username = models.CharField(max_length=100,null=False,blank=False,unique=True)
     password = models.CharField(max_length=100,null=False,blank=False)

class Model2(models.Model):
     name = models.ForeignKey(Model1, null=True)
     unique_str = models.CharField(max_length=50,null=False,blank=False,unique=True)
     city = models.CharField(max_length=100,null=False,blank=False)
     class Meta:
           unique_together = (('name', 'unique_str'),)

I've already filled 3 sample username-password in Model1 through django-admin page

In my views I'm getting this list as

userlist = Model1.objects.all()
#print userlist[0].username, userlist[0].password

for user in userlist:
     #here I want to get or create model2 object by uniqueness defined in meta class.
     #I mean unique_str can belong to multiple user so I'm making name and str together as a unique key but I dont know how to use it here with get_or_create method.
     #right now (without using unique_together) I'm doing this (but I dont know if this by default include unique_together functionality )
     a,b = Model2.objects.get_or_create(unique_str='f3h6y67')
     a.name = user
     a.city = "acity"
     a.save()

Answer 1

What I think you're saying is that your logical key is a combination of name and unique_together , and that you what to use that as the basis for calls to get_or_create() .

First, understand the unique_together creates a database constraint. There's no way to use it, and Django doesn't do anything special with this information.

Also, at this time Django cannot use composite natural primary keys, so your models by default will have an auto-incrementing integer primary key. But you can still use name and unique_str as a key.

Looking at your code, it seems you want to do this:

a, _ = Model2.objects.get_or_create(unique_str='f3h6y67', 
                                    name=user.username)
a.city = 'acity'
a.save()

On Django 1.7 you can use update_or_create() :

a, _ = Model2.objects.update_or_create(unique_str='f3h6y67', 
                                       name=user.username,
                                       defaults={'city': 'acity'})

In either case, the key point is that the keyword arguments to _or_create are used for looking up the object, and defaults is used to provide additional data in the case of a create or update. See the documentation .

In sum, to "use" the unique_together constraint you simply use the two fields together whenever you want to uniquely specify an instance.