Unit conversions between model field value and form field value

[Tim Bell]

Hi,

I have a model with an integer field storing a duration in hours, while I want to present that to users in a form in days. (The choice of these different units is imposed by other factors not under my control.)

So, when saving a form, I need to convert a value in days to hours by multiplying by 24. I've done that with a clean_<fieldname>() method on the form, as described at https://docs.djangoproject.com/en/2.2/ref/forms/validation/. That works fine for when saving a new model.

When editing an existing model however, I need to take the value from the model stored in hours, and convert that to days for display in the edit form. I've considered various places where I could do that conversion, for instance in the edit view, or the form __init__() method, or the model field's value_from_object() method, but none of those choices seem like the obvious choice, and I can't find a recommendation for how to do this either.

What would you suggest? And is the recommended approach actually documented somewhere that I've missed?

Thanks,

Tim

[Joe Reitman]

Hi Tim,

There is a 'Best Practices' guide for Django that recommends making models fat, https://django-best-practices.readthedocs.io/en/latest/applications.html#models. With that it would be logical to do both conversions in the model.

Regards,

Joe

[Shashank Singh]

One way could be make a custom read only field to show it in current value in days and take a custom field and on save_model take its value as days multiply it with 24 and save it in model's field.

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[Jani Tiainen]

Hi.

You could create custom form field that makes conversions both ways.

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