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nullable List field #107

shaicantor opened this issue May 29, 2016 · 2 comments


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commented May 29, 2016


When passing null in a List field, it is deserialized as [None]. (e.g. return [val])
Is there a way to for it to be deserialized as None without workarounds like pre_load or post_load decorators?

def get_value(data, name, field, allow_many_nested=False):
    """Get a value from a dictionary. Handles ``MultiDict`` types when
    ``multiple=True``. If the value is not found, return `missing`.

    :param object data: Mapping (e.g. :type:`dict`) or list-like instance to
        pull the value from.
    :param str name: Name of the key.
    :param bool multiple: Whether to handle multiple values.
    :param bool allow_many_nested: Whether to allow a list of nested objects
        (it is valid only for JSON format, so it is set to True in ``parse_json``
    missing_value = missing
    if allow_many_nested and isinstance(field, ma.fields.Nested) and field.many:
        if is_collection(data):
            return data
        missing_value = []

    if not hasattr(data, 'get'):
        return missing_value

    multiple = is_multiple(field)
    val = data.get(name, missing_value)
    if multiple and val is not missing:
        if hasattr(data, 'getlist'):
            return data.getlist(name)
        elif hasattr(data, 'getall'):
            return data.getall(name)
        elif isinstance(val, (list, tuple)):
            return val
        return [val]

    return val

@shaicantor shaicantor changed the title flaskparser nullable List field nullable List field May 29, 2016


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commented May 29, 2016

Thanks for reporting, @shaicantor . That certainly isn't the desired behavior; None should deserialize to None. The problem does appear to be in get_value, as you've suggested.

I would certainly review and merge a PR fixing this.

@sloria sloria closed this in 1a66d47 May 30, 2016


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commented May 30, 2016

This should now be fixed on dev.

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