Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"key":1,"lastLogin":[1,2,3,4]},{"key":2,"lastLogin":[5,52,33,44]},{"key":3,"lastLogin":17}]
Query
db.collection.update({lastLogin:{$type:"array"}},{$set:{lastLogin:{"$first":"lastLogin"}}})
Result