Room schema
var Room = new Schema({
    title:  String,
    author: String,
    body:   String,
    owners: [ { type: ObjectId, ref: "User", index: true } ]
})
Room.find({ owners: user })

first question: why can the query here be written this way? How to check the data in the database when it is written like this?
second question: what is the difference between the user.id effect and the one written above when I change it to the same effect?
Last question: is ObjectId automatically generated by MongoDB?