Add validation for model field name the same as the model name when using model inheritance

[willian]

class Place(models.Model):
    pass

class Restaurant(Place):
    restaurant = models.CharField(max_length=100)

When accessing Restaurant in the admin, a ValueError is Raised:

---

ValueError at /admin/questionnaire/restaurant/add/
Cannot assign "": "Restaurant.restaurant" must be a "Restaurant" instance.
---

[niall]

The super class has an attribute for each sub class with the same sub class but lower cased. This behavior is documented in the ​be careful with related name section of the model docs. The child elements will inherit inherit this attributes causing errors when you try to initialise an instance of that model (it thinks the fields are all related fields rather than say a CharField).

I'm guessing the models class should check for this and throw an exception when a field with the same lower case name as a subclass is defined.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Tim Graham]

This should include the case of child/parent models as described in #17043:

from django.db import models

class A(models.Model):
    pass

class B(A):
    pass

class C(A):
    b = models.BooleanField()

[Tim Graham]

​PR

[Tim Graham <timograham@…>]

In 4bc00de:

Fixed #14217 -- Added validation for field name collision when using model inheritance.