In Django - Model Inheritance - Does it allow you to override a parent model's attribute?


Question

I'm looking to do this:

class Place(models.Model):
   name = models.CharField(max_length=20)
   rating = models.DecimalField()

class LongNamedRestaurant(Place):  # Subclassing `Place`.
   name = models.CharField(max_length=255)  # Notice, I'm overriding `Place.name` to give it a longer length.
   food_type = models.CharField(max_length=25)

This is the version I would like to use (although I'm open to any suggestion): http://docs.djangoproject.com/en/dev/topics/db/models/#id7

Is this supported in Django? If not, is there a way to achieve similar results?

1
86
3/8/2018 5:49:01 PM

Accepted Answer

Updated answer: as people noted in comments, the original answer wasn't properly answering the question. Indeed, only the LongNamedRestaurant model was created in database, Place was not.

A solution is to create an abstract model representing a "Place", eg. AbstractPlace, and inherit from it:

class AbstractPlace(models.Model):
    name = models.CharField(max_length=20)
    rating = models.DecimalField()

    class Meta:
        abstract = True

class Place(AbstractPlace):
    pass

class LongNamedRestaurant(AbstractPlace):
    name = models.CharField(max_length=255)
    food_type = models.CharField(max_length=25)

Please also read @Mark answer, he gives a great explanation why you can't change attributes inherited from a non-abstract class.

(Note this is only possible since Django 1.10: before Django 1.10, modifying an attribute inherited from an abstract class wasn't possible.)

Original answer

Since Django 1.10 it's possible! You just have to do what you asked for:

class Place(models.Model):
    name = models.CharField(max_length=20)
    rating = models.DecimalField()

    class Meta:
        abstract = True

class LongNamedRestaurant(Place):  # Subclassing `Place`.
    name = models.CharField(max_length=255)  # Notice, I'm overriding `Place.name` to give it a longer length.
    food_type = models.CharField(max_length=25)
55
9/22/2018 1:07:58 AM

No, it is not:

Field name “hiding” is not permitted

In normal Python class inheritance, it is permissible for a child class to override any attribute from the parent class. In Django, this is not permitted for attributes that are Field instances (at least, not at the moment). If a base class has a field called author, you cannot create another model field called author in any class that inherits from that base class.


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