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POColumn comparison in Django queries
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copied!<p>I have a following model:</p> <pre><code>class Car(models.Model): make = models.CharField(max_length=40) mileage_limit = models.IntegerField() mileage = models.IntegerField() </code></pre> <p>I want to select all cars where mileage is less than mileage_limit, so in SQL it would be something like:</p> <pre><code>select * from car where mileage < mileage_limit; </code></pre> <p>Using Q object in Django, I know I can compare columns with any value/object, e.g. if I wanted to get cars that have mileage say less than 100,000 it would be something like:</p> <pre><code>cars = Car.objects.filter(Q(mileage__lt=100000)) </code></pre> <p>Instead of a fixed value I would like to use the column name (in my case it is mileage_limit). So I would like to be able to do something like:</p> <pre><code>cars = Car.objects.filter(Q(mileage__lt=mileage_limit)) </code></pre> <p>However this results in an error, since it is expecting a value/object, not a column name. Is there a way to compare two columns using Q object? I feel like it would be a very commonly used feature and there should be an easy way to do this, however couldn't find anything about it in the documentation.</p> <p><em>Note: this is a simplified example, for which the use of Q object might seam to be unnecessary. However the real model has many more columns, and the real query is more complex, that's why I am using Q. Here in this question I just wanted to figure out specifically how to compare columns using Q.</em></p> <p><b>EDIT</b></p> <p>Apparently after release of Django 1.1 it would be possible to do the following:</p> <pre><code>cars = Car.objects.filter(mileage__lt=F('mileage_limit')) </code></pre> <p>Still not sure if F is supposed to work together with Q like this:</p> <pre><code>cars = Car.objects.filter(Q(mileage__lt=F('mileage_limit'))) </code></pre>

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