CODEWITHSUNDEEP
pythondjangomodel
Tsangares
Tsangares

Reputation: 825

Django Model Field from OneToOneField

I have two models:

class FirstModel(models.Model):
     foo = models.IntegerField(default=0)
class SecondModel(models.Model):
     bar = models.OneToOneField(FirstModel, on_delete=models.CASCADE, primary_key=True)

How do I make a variable baz that is from FirstModel.foo?

I wish it was as easy as:

class SecondModel(models.Model):
     bar = models.OneToOneField(FirstModel, on_delete=models.CASCADE, primary_key=True)
     baz = bar.foo

Ultimate Goal: To get foo from an instance of SecondModel like second_model_instace.foo.

Upvotes: 1

Views: 1141

Answers (1)

DurgaDatta
DurgaDatta

Reputation: 4170

You can use related_name in the linking model for backward reference: 

class FirstModel(models.Model):
     foo = models.IntegerField(default=0)


class SecondModel(models.Model):
    bar = models.OneToOneField(
        FirstModel, 
        related_name='baz', 
        on_delete=models.CASCADE, 
        primary_key=True
    )

Now you can access as first_model_intance.baz if the link exists else you will get DoesNotExsist exception. The default is:

If you do not specify the related_name argument for the OneToOneField, Django will use the lower-case name of the current model as default value.

Update: If you want to get second_model_instace.foo, you do not even need related_name (backward reference). It is forward reference, which is already explicit. First get the first_model (via OneToOne Field) and then its attribute foo, that is:

second_model_instance.bar.foo

Upvotes: 3

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