Examples of how to implement inheritance with Django models

mples of how to implement inheritance with Django models

"""Examples of how to implement inheritance with Django models.

Idea here is DRY (don't repeat yourself). If models are similar, let them 
share functionality to the extent that its ancestrty makes sense. 

It's important to note is that because of the "abstract = True", Django knows 
not to create tables for those models, and instead only creates tables for 
those models that implement those abstract base classes.

It can also be noted that instead of having one gigantic, monolithic models.py
file, one can make models a module of itself:

myapp/
    models/
        __init__.py
        abstract.py
        item.py
        element.py
    views.py
    urls.py
    ...

And then, magically, in myapp/models/__init__.py:

from myproj.myapp.models.abstract import *
from myproj.myapp.models.item import *
from myproj.myapp.models.element import *

This establishes a sense of organization and maintainability within the app 
when models.py grows to be quite large, or really, in general.

This article is also helpful for automatically setting created_by/modified_by 
on save: http://haineault.com/blog/101/

"""

# optionally: base.py

class Base(models.Model):
    title = models.CharField(max_length=255)
    
    # User references
    created_by = models.CharField(max_length=100)
    modified_by = models.CharField(max_length=100)
    deleted_by = models.CharField(max_length=100)
    
    # Time references
    created_date = models.DateTimeField(auto_now_add=True)
    modified_date = models.DateTimeField(auto_now=True)
    deleted_date = models.DateTimeField(null=True, db_index=True)
    
    class Meta:
        abstract = True


# optionally: item.py

class Item(Base):
    item_field1 = models.CharField(max_length=100)
    item_field2 = models.CharField(max_length=200)
    
    class Meta:
        abstract = True
        
class PinkItem(Item):
    pink_item_field1 = models.CharField(max_length=100)
    pink_item_field2 = models.CharField(max_length=200)
    
class RoundItem(Item):
    round_item_field1 = models.CharField(max_length=100)
    round_item_field2 = models.CharField(max_length=200)


# optionally: element.py

class Element(Base):
    element_field1 = models.CharField(max_length=100)
    element_field2 = models.CharField(max_length=200)
    
    class Meta:
        abstract = True
        
class RedElement(Element):
    red_element_field1 = models.CharField(max_length=100)
    red_element_field2 = models.CharField(max_length=200)
    
class GreenElement(Element):
    green_element_field1 = models.CharField(max_length=100)
    green_element_field2 = models.CharField(max_length=200)