MongoDB Update array element (document with a key) if exists, else push

问题

I have such a schema:

doc:
{
    //Some fields
    visits:
    [
        {
            userID: Int32
            time: Int64
        }
    ]

}

I want to first check if a specific userID exists, if not, push a document with that userID and system time, else just update time value. I know neither $push nor $addToSet are not able to do that. Also using $ with upsert:true doesn't work, because of official documentation advice which says DB will use $ as field name instead of operator when trying to upsert.

Please guide me about this. Thanks

回答1:

You can use $addToSet to add an item to the array and $set to update an existing item in this array.

The following will add a new item to the array if the userID is not found in the array :

db.doc.update({
    visits: {
        "$not": {
            "$elemMatch": {
                "userID": 4
            }
        }
    }
}, {
    $addToSet: {
        visits: {
            "userID": 4,
            "time": 1482607614
        }
    }
}, { multi: true });

The following will update the subdocument array item if it matches the userId :

db.doc.update({ "visits.userID": 2 }, {
    $set: {
        "visits.$.time": 1482607614
    }
}, { multi: true });

来源：https://stackoverflow.com/questions/41316056/mongodb-update-array-element-document-with-a-key-if-exists-else-push