Obviously I was tired when I wrote this. I apologize for the
grammatical errors, which were a-plenty.
On Feb 12, 5:51 pm, Russell Keith-Magee <freakboy3...@gmail.com>
wrote:
> On Thu, Feb 12, 2009 at 10:17 PM, django_fo...@codechimp.net
>
>
>
> <codech...@gmail.com> wrote:
>
> > I wanted to get the communities thoughts on this subject. I am
> > working on a simple site that has news articles, each of which has a
> > reference to a User object provided by django.contrib.auth that is the
> > author of the news article. This is done right now using the
> > following code:
>
> > class NewsArticle(models.Model):
> > subject = models.CharField(max_length=1024)
> > author = models.ForeignKey(User)
> > body = models.TextField()
> > publish_date = models.DateTimeField('date published')
>
> > As expected, the SQL produced stores the key of the User table in the
> > News table.
>
> > However, when you try to serialize this with the built-in JSON
> > serializer, it doesn't traverse the objects. Instead, what you get is
> > something like this:
>
> > [
> > {"pk": 1,
> > "model": "news.newsarticle",
> > "fields": {
> > "body": "This is my very first news article!\r\nIt has some news
> > stuff in it",
> > "author": 1, "publish_date": "2009-02-09 16:09:22",
> > "subject": "My first news article!"
> > }},
> > {"pk": 2,
> > "model": "news.newsarticle",
> > "fields": {
> > "body": "Some more news for you...",
> > "author": 1,
> > "publish_date": "2009-02-11 08:08:36",
> > "subject": "Some more news for you"
> > }
> > }]
>
> > Notice author just simply prints out the ID. This is due to the lazy-
> > nature of the serializers. I have done some reading on the Internets,
> > and from what I can tell there are a few options here:
> > 1) Write a custom serializer to do this. There are some examples
> > out there, but the down side is you have to support the code
> > yourself. Compatibility with client-side libraries might be a
> > factor.
> > 2) Make multiple calls...one to get the News, then one to get each
> > author. This could get expensive and cause the interface to
> > feel
> > sluggish since calls to the backend would grow exponentially.
>
> These two options are really just the same thing, described at
> different levels (unless, when you say "custom serializer", you mean
> writing your own JSON library or changing the format in which Django
> serializes objects). If you write a custom serializer that follows
> relationships, you're really just writing code to make multiple
> queries and pass it to the serialization engine.
>
> This general idea has been proposed in the past (ticket #4656), and
> one of these days someone may get around to implementing it.
>
> If you want to roll this yourself, and you only need to serialize this
> model specifically, you actually only need 2 queries - one to retrieve
> the News you want, then one to retrieve the Authors related to that
> news. The __in operator is your friend here. The general case (which
> could have News objects pointing to other News objects, or Author
> objects pointing to any other object) may require multiple calls. The
> delete() operation does exactly the same object traversal, and while
> it isn't cheap, it isn't exponential.
>
> Yours,
> Russ Magee %-)
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