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copied!<p>One way is to add a setter for the state. It's just a normal method, nothing special.</p> <pre><code>class Game(models.Model): # ... other code def set_state(self, newstate): if self.state != newstate: oldstate = self.state self.state = newstate if oldstate == 'S' and newstate == 'A': self.started = datetime.now() # create units, etc. </code></pre> <p><strong>Update:</strong> If you want this to be triggered <em>whenever</em> a change is made to a model instance, you can (<em>instead</em> of <code>set_state</code> above) use a <code>__setattr__</code> method in <code>Game</code> which is something like this:</p> <pre><code>def __setattr__(self, name, value): if name != "state": object.__setattr__(self, name, value) else: if self.state != value: oldstate = self.state object.__setattr__(self, name, value) # use base class setter if oldstate == 'S' and value == 'A': self.started = datetime.now() # create units, etc. </code></pre> <p>Note that you wouldn't especially find this in the Django docs, as it (<code>__setattr__</code>) is a standard Python feature, documented <a href="http://docs.python.org/reference/datamodel.html?highlight=__setattr__#object.__setattr__" rel="noreferrer">here</a>, and is not Django-specific.</p> <p>note: Don't know about versions of django older than 1.2, but this code using <code>__setattr__</code> won't work, it'll fail just after the second <code>if</code>, when trying to access <code>self.state</code>.</p> <p>I tried something similar, and I tried to fix this problem by forcing the initialization of <code>state</code> (first in <code>__init__</code> then ) in <code>__new__</code> but this will lead to nasty unexpected behaviour.</p> <p>I'm editing instead of commenting for obvious reasons, also: I'm not deleting this piece of code since maybe it could work with older (or future?) versions of django, and there may be another workaround to the <code>self.state</code> problem that i'm unaware of</p>

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