更新mongodb中的多个文档

Question

我有一个名为“ mycustomers”的数据库，该数据库具有一个名为“ customers”的集合

数据库当前具有这些文档

我已经执行了该查询

db.customers.update({}, {$currentDate: {TimeStamp: {$type: "date"}}});

为什么此语句不能更新集合中的所有文档？

结果在下面

{
    "_id" : ObjectId("5b3504203abb335c552137b7"),
    "gender" : "male",
    "Timestamp" : ISODate("2018-06-30T11:36:14.516Z")
}

{
    "_id" : ObjectId("5b3505533abb335c552137b8"),
    "first_name" : "John",
    "gender" : "male"
}



{
    "_id" : ObjectId("5b3505533abb335c552137b9"),
    "first_name" : "Steven",
    "gender" : "male"
}




{
    "_id" : ObjectId("5b3505533abb335c552137ba"),
    "first_name" : "Lady",
    "gender" : "female"
}




{ "_id" : ObjectId("5b3732f990418e4b51b563d4") }




{ "_id" : ObjectId("5b3733d790418e4b51b563da") }