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    <p>The main issue has to do with side effects that are wanted or not. And with variables really being pointers to objects in Python.</p> <p>When you create an object out of a model, it doesn't have a primary key yet as you haven't saved it yet. But, when saving it, should Django have to make sure it updates attributes on the already-existing object? A primary key is logical, but it would also lead you to expect other attributes being updated.</p> <p>An example for that is Django's unicode handling. Whatever charset you give the text you put into a database: Django gives you unicode once you get it out again. But if you create an object (with some non-unicode attribute) and save it, should Django modify that text attribute on your existing object? That already sounds a little bit more dangerous. Which is (probably) why Django doesn't do any on-the-fly updating of objects you ask it to store in the database. </p> <p>Re-loading the object from database gives you a perfect object with everything set, but it also makes your variable point to a different object. So that would not help in your example in case you already gave the Rating a pointer at your "old" Movie object.</p> <p>The <code>Movie.objects.create(title="The Hobbit")</code> mentioned by Hedde is the trick here. It returns a movie object <em>from the database</em>, so it already has an id.</p> <pre><code>the_hobbit = Movie.objects.create(title="The Hobbit") my_rating = Rating(movie=the_hobbit, rating=8.5) # No need to save the_hobbit, btw, it is already saved. my_rating.save() </code></pre> <p>(I had problems with the difference between my objects and objects from the database, too, when my newly created object didn't output unicode. The <a href="http://reinout.vanrees.org/weblog/2011/11/18/django_unicodedecodeerror.html">explanation</a> I put on my weblog is the same as above, but worded a bit differently.)</p>
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    1. POWhen does Django look up the primary key of foreign keys?
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    1. USReinout van Rees
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    1. COsounds like a plausible cause +1
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      1. USHedde van der Heide
    2. CO+1 I think this is the correct answer to the question as it answers the theoretical aspect
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