MongoDB - Update or Insert object in array

问题:

I have the following collection

{
    "_id" : ObjectId("57315ba4846dd82425ca2408"),
    "myarray" : [ 
             {
                userId : ObjectId("570ca5e48dbe673802c2d035"),
                point : 5
             },
             {
                userId : ObjectId("613ca5e48dbe673802c2d521"),
                point : 2
             },        
     ]
}

These are my questions

I want to push into myarray if userId doesn't exist, it should be appended to myarray. If userId exists, it should be updated to point.

I found this

db.collection.update({
  _id : ObjectId("57315ba4846dd82425ca2408"), "myarray.userId" :  ObjectId("570ca5e48dbe673802c2d035")
},{
   $set: {"myarray.$.point": 10}
})

But if userId doesn't exist, nothing happens.

and

db.collection.update({
  _id : ObjectId("57315ba4846dd82425ca2408")
},{
  $push: {"myarray": {userId: ObjectId("570ca5e48dbe673802c2d035"), point: 10}}
})

But if userId object already exists, it will push again.

What is the best way to do this in MongoDB?

回答1:

Try this

db.collection.update(
    { _id : ObjectId("57315ba4846dd82425ca2408")},
    { $pull: {"myarray.userId": ObjectId("570ca5e48dbe673802c2d035")}}
)
db.collection.update(
    { _id : ObjectId("57315ba4846dd82425ca2408")},
    { $push: {"myarray": {
        userId:ObjectId("570ca5e48dbe673802c2d035"),
        point: 10
    }}
)

回答2:

The accepted answer by Flying Fisher is that the existing record will first be deleted, and then it will be pushed again.

A safer approach (common sense) would be to try to update the record first, and if that did not find a match, insert it, like so:

// first try to overwrite existing value
var result = db.collection.update(
   {
       _id : ObjectId("57315ba4846dd82425ca2408"),
       "myarray.userId": ObjectId("570ca5e48dbe673802c2d035")
   },
   {
       $set: {"myarray.$.point": {point: 10}}
   }
);
// you probably need to modify the following if-statement to some async callback
// checking depending on your server-side code and mongodb-driver
if(!result.nMatched)
{
    // record not found, so create a new entry
    // this can be done using $addToSet:
    db.collection.update(
        {
            _id: ObjectId("57315ba4846dd82425ca2408")
        },
        {
            $addToSet: {
                myarray: {
                    userId: ObjectId("570ca5e48dbe673802c2d035"),
                    point: 10
                }
            }
        }
    );
    // OR (the equivalent) using $push:
    db.collection.update(
        {
            _id: ObjectId("57315ba4846dd82425ca2408"),
            "myarray.userId": {$ne: ObjectId("570ca5e48dbe673802c2d035"}}
        },
        {
            $push: {
                myarray: {
                    userId: ObjectId("570ca5e48dbe673802c2d035"),
                    point: 10
                }
            }
        }
    );
}

This should also give (common sense, untested) an increase in performance, if in most cases the record already exists, only the first query will be executed.

回答3:

Unfortunately "upsert" operation is not possible on embedded array. Operators simply do not exist so that this is not possible in a single statement.Hence you must perform two update operations in order to do what you want. Also the order of application for these two updates is important to get desired result.