Method get_<field>display() returns incorrectly in queries

[ripperdoc]

I have a document called Product, and call the Mongoengine provided convenience method get_type_display() to return the correct display name of the current choice for the field "type".

This works when I display a single Product, but when displaying this for each Product in a QuerySet, it returns a default value for all fields. So the result is:

print product.type => 'digital'
print product.get_type_display() => 'item'  (incorrect value)
print product._BaseDocument__get_field_display(self._fields['type'])  => 'digital' (the correct value)

I was not able to find the root cause of the error, but want to start this issue thread to get some pointers. Right now, I'm using the last line in above example as a workaround.

[lafrech]

Random guess: anything to do with 'type' being a reserved word? Does this happen with any field name?

[ripperdoc]

I checked, it happens to fields named "type", "status", "currency" so I assume that is more than reserved words, and it only happens when I iterate over the QuerySet.

[lafrech]

OK. Thanks for checking.

[dibrovsd]

BaseDocument.__get_field_display
value = getattr(self, field.name) return value from last document in query.
Maybe it's cached?

but override __getattr__ can't find :-(

monkey patch (work) is

def choice_verbose(self, attr_name):
    u"""
    get_{field}_display() у mongoengine Не работает на выборках из querySet-а.
    Корректно отрабатывает только на одиночном документе.
    Пока что вот такой вот костыль
    """
    cls = self.__class__
    choices = dict(getattr(cls, attr_name).choices)
    val = getattr(self, attr_name)
    return choices.get(val, val)

[tomasgarzon]

Hi, I can't find this error fixed in any Pull Request, will it be included in the next release? is there any plan to fix it?

[julianwachholz]

This is definitely a bug, the cause is in how the get_%s_display method is created in __set_field_display, setting the display function to a partial of the instance self, instead of the document class:

setattr(obj,
    'get_%s_display' % attr_name,
    partial(self.__get_field_display, field=field))

This causes the get_%s_display function to always be called with self as the last Document that was created.

[wojcikstefan]

This was fixed by #1419