如何将 CodecOptions 应用于 mongoengine 集合以获取 tzinfo？

Question

Using a mongoengine Document , when I load a DateTimeField from mongo, it lacks tzinfo . Our application by policy wants all datetimes to have tzinfo .

When I save to mongo, I know that pymongo does the correct and predictable thing wrt timezones; if it is naive, it is stored as a UTC time, if it has a timezone, it is converted to UTC and then stored as UTC time. All good so far.

When I load, though, DateTimeField always gives me a naive datetime . I know that this datetime is in UTC, so I could add the tzinfo if I wanted, but I'd have to do this in dozens of places in my application, and it's a guarantee of future timezone bugs, unless I use a custom field type (see example below).

Referencing: https://api.mongodb.com/python/current/examples/datetimes.html I know that pymongo supports putting the tzinfo onto the object as it arrives from the database. I also know that I can do this myself, as the following minimal example shows. The DateTimeTZField adds tzinfo in to_python .

from datetime import datetime

from mongoengine import connect, Document, fields

from pytz import timezone

def utcnowTZ():
    return datetime.utcnow().replace(tzinfo=timezone('UTF'))

class DateTimeTZField(fields.DateTimeField):
    """
    This seems like a hack. I would like to use CodecOptions instead
    """
    def to_python(self, value):
        converted = super(DateTimeTZField, self).to_python(value)
        return converted.replace(tzinfo=timezone('UTC'))

class Thing(Document):
    dtTZ = DateTimeTZField(default=utcnowTZ)
    dtXX = fields.DateTimeField(default=utcnowTZ)

connect(host="mongodb://localhost/datetimewithtz")
Thing.objects().delete()

t1 = Thing()
print '%r.dtXX (default): %s' % (t1, t1.dtXX)
print '%r.dtTZ (default): %s' % (t1, t1.dtTZ)
t1.save()
print 'saved %r' % t1.id; print
t1 = Thing.objects(id=t1.id).first()
print 'reloaded %r' % t1.id
print '%r.dtXX (loaded ): %s' % (t1, t1.dtXX)
print '%r.dtTZ (loaded ): %s' % (t1, t1.dtTZ)

Without replacing DateTimeField throughout my application, is there a way to use bson CodecOptions to make this apply globally to all DateTimeFields: when loaded from the database, they should have tzinfo attached ?

Answer 1

How about

connect(...,  tz_aware=True,...)

the parameter will be forwarded to MongoClient(..., tz_aware=True, ...)

Answer 2

My understanding is that mongoengine doesn't support per-model codec_options . If it did, they should be part of the opts dictionary here .

However, PyMongo defaults to the Database's codec_options when the Collection doesn't have any of it's own, and you can set these by manually calling register_connection in your application before you make any requests to the DB.

In your example above you should pass the codec_options like this:

with_timezone = CodecOptions()
connect(host="mongodb://localhost/datetimewithtz", codec_options=with_timezone)