How to sort a List(Nested()) based on data not available in the dumped version?

[ThiefMaster]

I have a list of nested objects which have a property that can act as a sort key. However, that property is not part of the schema since it's not useful in the dumped version.

I'm looking for a way to sort the data using this property.

• pre_dump won't work because i'd need to modify the actual object to be dumped - not a good idea in case of ORM model instances
• post_dump won't work because i don't have the data
• post_dump(pass_original=True) would be cumbersome because i'd have to get the order from the original ones but then apply it to the dumped data

The ideal option would be a way to intercept how the data for the List() gets loaded. That way I could simply return a sorted list without touching the original one. Is there already a way to do that? Something like @get_value('mylistattribute') to override how it gets loaded from the data-to-be-dumped? The only other alternative I see is subclassing List and add sorting support in there...

[ThiefMaster]

FWIW this is what I ended up using, but if there's a better way please let me know:

class SortedList(fields.List):
    """
    Like the normal List, but when dumping a sort key can be specified.
    This allows sorting the data even without having the information needed
    for sorting in the final dumped data.
    """

    def __init__(self, *args, sort_key, **kwargs):
        self.sort_key = sort_key
        super().__init__(*args, **kwargs)

    def _serialize(self, value, attr, obj, **kwargs):
        if value is None:
            return None
        value = sorted(value, key=self.sort_key)
        return super()._serialize(value, attr, obj, **kwargs)