How to push an existing sub-document into an embedded array in MongoDB?

Question

I'm trying to determine if the following use case is feasible in MongoDB 3.4: I have a collection containing documents with a schema similar to this:

{
    "_id": ObjectId("..."),
    "data": {
        "fname": "John",
        "lname": "Doe"
    },
    "history": []
}

The data field is meant to hold the current state of the entity and the history array is meant to hold the most recent versions of it (accounting for the max document size and for querying purposes).

When an update operation is issued from application logic, I would like to $push the data field into the history array and the replace it with the new state of the entity. I haven't been able to find anything about this on the MongoDB docs and every question I found on SO deals with pushing a totally new object into an array, not "moving" an existing field's value. Is it possible to reference a document field in a $push operation like this?

Answer 1

db.collection.update({"_id": "1234"}, {"$set": {"data": {"data-value"}}}, {"$push": {"history": {"history-value"}})

你可以这样写，它会自动将值推送到历史记录中，并将数据更改为当前状态。