MongoDB - Update or Insert object in array

Question

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?

Answer 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     }} ) 

Explination: in the first statment $pull removes the element with userId= ObjectId("570ca5e48dbe673802c2d035") from the array on the document where _id = ObjectId("57315ba4846dd82425ca2408")

In the second one $push inserts this object { userId:ObjectId("570ca5e48dbe673802c2d035"), point: 10 } in the same array.

Answer 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.