Switch collection in mongoengine for find query

问题

I've read mongoengine documentation about switching collection to save document. And test this code and it worked successfully:

from mongoengine.context_managers import switch_db

class Group(Document):
    name = StringField()

Group(name="test").save()  # Saves in the default db

with switch_collection(Group, 'group2000') as Group:
    Group(name="hello Group 2000 collection!").save()  # Saves in group2000 collection

But the problem is when I want to find saved document in switch collection switch_collection doesn't work at all.

with switch_collection(Group, 'group2000') as GroupT:
    GroupT.objects.get(name="hello Group 2000 collection!")  # Finds in group2000 collection

回答1:

As of mongoengine==0.10.0 mongoengine.context_managers.switch_collection(cls, collection_name) used as "with switch_collection(Group, 'group1') as Group:" in the example doesn't work inside functions. It gives unboundlocalerror. A simple get around with existing resources is :

To get:

new_group = Group.switch_collection(Group(),'group1')
from mongoengine.queryset import QuerySet
new_objects = QuerySet(Group,new_group._get_collection())

Use new_objects.all() to get all objects etc.

To save:

group_obj = Group()
group_obj.switch_collection('group2')
group_obj.save()

回答2:

Although Prachetos Sadhukhan answer works for me, I prefer to get the collection directly, not relying on private _get_collection method:

from mongoengine import connection
new_group_collection = connection.get_db()['group1']
from mongoengine.queryset import QuerySet
new_objects = QuerySet(Group, new_group_collection)

来源：https://stackoverflow.com/questions/26698471/switch-collection-in-mongoengine-for-find-query