As per http://docs.mongodb.org/manual/reference/operators mongodb allows specification of multiple fields for

$unset

operator. Mongoid, however, seems to only allow a single field for this operation

For example, the following code works as expected:

Person.where(tag: 'some tag').unset('name')
Person.where(tag: 'some tag').unset('age')

`

But the code below does not. Instead it fails without an error. 

Ruby
Person.where(tag: 'some tag').unset(['name', 'age'])

UPDATE: The Moped version of the command works fine though:

Ruby
Person.collection.find(tag: 'some tag').update_all('$unset' =>

)
`