MongoDB (Mongoose) update element in array of array

Question

I'm currently building a REST-Api with node.js express and can't figure out how to update / add elements to the scores Array.

Here is one document from my MongoDB collection (how it should look):

field

My mongoose model:

const challengesSchema = new mongoose.Schema({
 createdBy:{
 type:String,
 required: true
 },
 mapType:{
 type:String,
 required: true
 },
 time:{
 type:Number,
 required: true
 },
 numberOfMaps:{
 type:String,
 required: true
 },
 maps:{
 type:Array,
 required: true
 },
 pin:{
 type: String,
 required: true
 },
 takenBy:{
 type: Array,
 required: false
 }
})

Basically I receive an id, which I can use to do Challenges.findById({challenge._id}) . I figured out how to add an object to the takenBy Array, like so:

Challenges.findOneAndUpdate(
 { _id: challenge._id },
 {
 $push: {
 takenBy: user
 }
 }
);

How can I add an element (score, like "20") to the scores array in the array 'takenBy' ?

Answer 1

You can push score and calculate the new TotalScore in one go using filtered positional operator $ like this.

router.put("/challenges/:id/:scoreId", async (req, res) => {
 let score = req.body.score;
 try {
 let result = await Challenges.findByIdAndUpdate(
 req.params.id,
 {
 $push: { "takenBy.$[inner].scores": score },
 $inc: {
 "takenBy.$[inner].TotalScore": score
 }
 },
 {
 arrayFilters: [{ "inner._id": req.params.scoreId }],
 new: true
 }
 );
 if (!result) return res.status(404);
 res.send(result);
 } catch (err) {
 console.log(err);
 res.status(500).send("Something went wrong");
 }
});

Test:

Let's have this existing document:

{
 "_id" : ObjectId("5e08fe4c0bc1b932e8726a0f"),
 "maps" : [ ],
 "takenBy" : [
 {
 "_id" : "id1",
 "TotalScore" : NumberInt(100),
 "scores" : [
 NumberInt(20),
 NumberInt(60),
 NumberInt(20)
 ]
 },
 {
 "_id" : "id2",
 "TotalScore" : NumberInt(30),
 "scores" : [
 NumberInt(10),
 NumberInt(20)
 ]
 }
 ],
 "createdBy" : "5dfe0...",
 "mapType" : "World",
 "time" : NumberInt(2),
 "numberOfMaps" : "2",
 "pin" : "9558",
 "__v" : NumberInt(0)
}

If we want to add a score of 50 to then id1, we send a PUT request (http://..../challenges/5e08fe4c0bc1b932e8726a0f/id1) with this body:

{
 "score": 50
}

The result will be like this:

{
 "_id" : ObjectId("5e08fe4c0bc1b932e8726a0f"),
 "maps" : [ ],
 "takenBy" : [
 {
 "_id" : "id1",
 "TotalScore" : NumberInt(150),
 "scores" : [
 NumberInt(20),
 NumberInt(60),
 NumberInt(20),
 NumberInt(50)
 ]
 },
 {
 "_id" : "id2",
 "TotalScore" : NumberInt(30),
 "scores" : [
 NumberInt(10),
 NumberInt(20)
 ]
 }
 ],
 "createdBy" : "5dfe0...",
 "mapType" : "World",
 "time" : NumberInt(2),
 "numberOfMaps" : "2",
 "pin" : "9558",
 "__v" : NumberInt(0)
}

As you see the score is added to the related item array, and it's TotalScore is also incremented by 50 giving the TotalScore 150

• kevinunger: Thanks! Awesome approach! Is there a way I could not just push to the scores array, but can specify the index where to put my new score in that array?
• SuleymanSah: @user2557097 yes it seems possible, please have a look at the docs
• kevinunger: thanks, it works! Like this: $push: { "takenBy.$[inner].scores": { $each: [score], $position: scorePosition }, },
• SuleymanSah: @user2557097 great:) You did it by yourself. Please reconsider to accept this answer, this is the way how we update in mongoose.
• kevinunger: I accepted your answer. Thanks again! Another problem I can't figure out: The premise of my question was that the takenBy array has objects with ids in it. When the user hasn't submitted a score, it does not add a score. Is there a way to create the object in the taken by array with the corresponding score array and TotalScore in one query? I could find the field and search for the Object with the id, if it exists, execute your query, if not create a new field. Is there a way to do this in one query?

Answer 2

You can retrieve the object first:

const updateChallenge = async (req,res) => {
 const challenge = await Challenges.findById(id);
 // Then you make duly changes to it with vanilla js:
 // Find which element in the array takenBy to update 
 // with regular js, methods like filter work or hardcode it
 challenge.takenBy[1].push(newElement);
 await challenge.save();
 // DONE! :)
}

Of course you can use destructuring if you prefer!

Answer 3

...how to update / add elements to the scores Array.

I would first retrieve that array... Push the new value, then update.

Something like:

Challenges.findById(challenge._id,(err, db_result) => {
 if(err){
 console.log(err) // error management
 //...
 }
 if(db_result){
 // Get the takenBy array
 let takenBy = db_result.takenBy
 // Who are we talking about... You need the second _id for that record
 let who_id = user._id
 let targetIndex = null
 let byWho = takenBy.filter((who, index) => {
 let gotYa = who._id === who_id
 if (gotYa){
 targetIndex = index
 }
 return gotYa // Boolean used as a return for .filter()
 })
 if(byWho.length>0){
 console.log("Got someone... Index: ", targetIndex)
 }else{
 console.log("No one found?")
 return
 }
 // Push the new value using the index where to update.
 takenBy[targetIndex].scores.push(challenge.score)
 Challenges.updateOne({_id:challenge._id},{
 $set: {
 takenBy: takenBy
 }
 }, (err, data) => {
 console.log(data)
 }
 )
 }
});

• Louys Patrice Bessette: Ho, I missed the fact the score array is in the takenBy array... I will update my answer. But the concept is the same. It's get, push, set. ;)
• Louys Patrice Bessette: hahem... Maybe you have to target the right takenBy element... Do you have the second id for it? Hold on a bit more... I'm editing
• Louys Patrice Bessette: Try that... ;) We should be close.
• kevinunger: It finally works! The problem in the end was that the updateOne function only changes the database document, when it has a callback function, like you did in the first line. I found this link. So everything works now, thanks!
• Louys Patrice Bessette: Mind to accept the answer then? I'm happy for you. Enjoy coding!