Issues with MapField and _fields_to_dbfields

[AlJohri]

I have a model defined with a MapField.

class Race(Document):
    raceUID = StringField(primary_key=True)
    electionDate = StringField()
    statePostal = StringField()

    historical_reporting_units = MapField(ListField(EmbeddedDocumentField(ReportingUnit)))
    current_reporting_units = MapField(field=EmbeddedDocumentField(ReportingUnit))

When trying to project the result to only include a certain key within the MapField like so: Race.objects(raceUID="2016-03-01-MA-24548").only("current_reporting_units.state-MA").first()

I get the following stack trace. I believe it should skip trying to resolve the dbfield attribute for MapFields.

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-10-9098a246470f> in <module>()
      1 from electionbot2016.models import Race, ReportingUnit
----> 2 race = Race.objects(raceUID="2016-03-01-MA-24548").only("current_reporting_units.state-MA").first()
      3 for unit in race.current_reporting_units:
      4     print(unit)

/Users/johria/anaconda/lib/python3.5/site-packages/mongoengine/queryset/base.py in only(self, *fields)
    810         fields = dict([(f, QueryFieldList.ONLY) for f in fields])
    811         self.only_fields = list(fields.keys())
--> 812         return self.fields(True, **fields)
    813 
    814     def exclude(self, *fields):

/Users/johria/anaconda/lib/python3.5/site-packages/mongoengine/queryset/base.py in fields(self, _only_called, **kwargs)
    864         for value, group in itertools.groupby(fields, lambda x: x[1]):
    865             fields = [field for field, value in group]
--> 866             fields = queryset._fields_to_dbfields(fields)
    867             queryset._loaded_fields += QueryFieldList(
    868                 fields, value=value, _only_called=_only_called)

/Users/johria/anaconda/lib/python3.5/site-packages/mongoengine/queryset/base.py in _fields_to_dbfields(self, fields)
   1659             try:
   1660                 field = ".".join(f.db_field for f in
-> 1661                                  document._lookup_field(field.split('.')))
   1662                 ret.append(field)
   1663             except LookUpError as err:

/Users/johria/anaconda/lib/python3.5/site-packages/mongoengine/queryset/base.py in <genexpr>(.0)
   1658         for field in fields:
   1659             try:
-> 1660                 field = ".".join(f.db_field for f in
   1661                                  document._lookup_field(field.split('.')))
   1662                 ret.append(field)

AttributeError: 'str' object has no attribute 'db_field'

Am I using the only function wrong? Can I manually input a raw projection for the timebeing?

EDIT: added current_reporting_units to Race model

[AlJohri]

I worked around the issue for now by manually changing the _loaded_fields attribute.

query = Race.objects(raceUID="2016-03-01-MA-24548")
query._loaded_fields.fields.add('historical_reporting_units.state-MA')
race = query.first()

[lafrech]

Hi.

current_reporting_units is not defined in the document. At least in the definition you're showing, there is only historical_reporting_units, no current_reporting_units field.

What do you expect from

Race.objects(raceUID="2016-03-01-MA-24548").only("current_reporting_units.state-MA")

?

[AlJohri]

class Race(Document):
    raceUID = StringField(primary_key=True)
    electionDate = StringField()
    statePostal = StringField()

    historical_reporting_units = MapField(ListField(EmbeddedDocumentField(ReportingUnit)))
    current_reporting_units = MapField(field=EmbeddedDocumentField(ReportingUnit))

sorry I missed that line

[AlJohri]

Regardless, it would error out on:

Race.objects(raceUID="2016-03-01-MA-24548").only("historical_reporting_units.state-MA")

as well because they are both MapFields

[AlJohri]

@lafrech would you like me to reiterate the issue?

[lafrech]

What do you mean by "reiterate"?

If you mean provide a complete test case, maybe even a branch with this test added to the automatic tests, you are more than welcome.

Thanks.

[wojcikstefan]

Fixed by #1553