Re: What are the advantages of Model inheritance?

Thu, 23 Jun 2011 13:59:24 -0700

I might be wrong here, but I'm fairly sure that the below example you pasted is invalid code (i.e. you need to add a proxy _meta??).

My apologies if I'm wrong though, as I have never encountered a need to do this before, and just going off vague memory.

Cal

On 23/06/2011 19:24, Rich Jones wrote: 
Other than the convenience of writing them, I can't seem to find any
advantages of using model inheritance.

Please allow me to explain the trouble I am having with an example.
Suppose,

class Post(models.Model):
    title = models.CharField(max_length=200)
    user_owner_id = models.ForeignKey(User)

    def __unicode__(self):
        return self.title

class BetterPost(Post):
    description = models.CharField(max_length=200)

    def __unicode__(self):
        return self.title

Now, in the template:

{% with profile.user.post_set.select_related as posts %}
    {% for post in posts %}
        {{post}}
    {% empty %}
        No posts!
    {% endfor %}
{% endwith %}

{% with profile.user.betterpost_set.select_related as posts %}
    {% for post in posts %}
        {{post}}
    {% empty %}
        No posts!
    {% endfor %}
{% endwith %}

If there are 2 'Posts' and 1 'BetterPost', the template code will
print all of the posts in the first loop, then none in the second loop
set.

So why would I use model inheritance if this is the kind of behavior I
can expect? If I can't get a set and can't access the fields, why
wouldn't I just copy the fields into BetterPost rather than extending
Post?

Thank you for reading!
R

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