ZCCADCDEDB567ABAE643E15DCF0974E503Z - 如何在数组中添加和返回值的总和

Question

This is the schema that I have:

let postScheme = new Schema({
    title: {
        type: String,
        required: true
    },
    body: String,
    isImage: Boolean,
    imageUrl: String,
    icon: String,
    time: {
        type: String,
        required: true
    },
    username: {
        type: String,
        required: true
    },
    votes: [{tag: String, votes: Number}], //array of {tag, votes}
    usersVoted: Array,
    tags: Array, //array of tags
})

and Im retrieving multiple documents using (Post is the model):

Post.find({username: 'example'})

I want the votes.votes value from each document to be totaled into one count. How can this be achieved?

Answer 1

You can use $sum opeator:

let result = Post.aggregate([
    { $match: {username: 'example'} },
    { $addFields: { totalCount: { $sum: "$votes.votes" } } }
])

Answer 2

The method @mickl has mentioned works well if you would like the sum of the array for that object only (ie, for each post). Pointing that out if that helps anyone.

I was looking to have all the values summed into one single variable, and unwinding it has made it possible as shown here:

Post.aggregate([
                { $match: { username: 'example' } },
                { $unwind: {path: '$votes'}},
                { $group: {_id: null, totalVotes: {$sum: '$votes.votes'}}}
            ])
            .exec((err, result) => {
                if (err) {
                    //err stuff
                }

                let totalVotes = result[0].totalVotes //The sum of all the votes.votes
                
            })