In Django, how can I order by a multiple-choice CharField in arbitrary not alphabetical order?
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Imagine a model `Shirts` with a `size` CharField, with values limited to a small number of choices, e.g. 'small', 'medium', 'large', 'xlarge' etc.

To get the shirts grouped by size, you'd do:

    Shirts.objects.order_by('size')

But Django will (naturally) order the groups alphabetically, i.e. 'large' then 'medium' then 'small' then 'xlarge'. What I want is to have 'small' before 'medium' before 'large' etc. 

I.e. what I naturally want to do is something like the following pseudocode:

    size_order = {'small': 1, 'medium': 2, 'large': 3, 'xlarge': 4}
    Shirts.objects.order_by('size_order[size]')

What's the best way to accomplish this?
