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POCustom Sorting on Custom Field in Django
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copied!<p>In my app, I have defined a custom field to represent a physical quantity using the <a href="http://pypi.python.org/pypi/quantities" rel="nofollow">quantities</a> package. </p> <pre><code>class AmountField(models.CharField): def __init__(self, *args, **kwargs): ... def to_python(self, value): create_quantities_value(value) </code></pre> <p>Essentially the way it works is it extends CharField to store the value as a string in the database </p> <pre><code>"12 min" </code></pre> <p>and represents it as a quantities object when using the field in a model</p> <pre><code>array(12) * min </code></pre> <p>Then in a model it is used as such:</p> <pre><code>class MyModel(models.Model): group = models.CharField() amount = AmountField() class Meta: ordering = ['group', 'amount'] </code></pre> <p>My issue is that these fields do not seem to sort by the quantity, but instead by the string.</p> <p>So if I have some objects that contain something like </p> <ul> <li>{"group":"A", "amount":"12 min"}</li> <li>{"group":"A", "amount":"20 min"}</li> <li>{"group":"A", "amount":"2 min"}</li> <li>{"group":"B", "amount":"20 min"}</li> <li>{"group":"B", "amount":"1 hr"}</li> </ul> <p>they end up sorted something like this: </p> <pre><code>>>> MyModel.objects.all() [{A, 12 min}, {A, 2 min}, {A, 20 min}, {B, 1 hr}, {B, 20 min}] </code></pre> <p>essentially alphabetical order.</p> <p>Can I give my custom AmountField a comparison function so that it will compare by the python value instead of the DB value?</p>

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