MongoDB Searching if element exist in array

Question

So I have something like Survey Schema (I am using mongoose).

In this Schema, for each voting option, I have votes[] array that contains ObjectIds of Users.

Now I want to check if User can vote again, or if he already voted?

The simple solution is iterating thru votes with .indexOf() and checking if id exists. Now this is a blocking way for Node JS, since this operation is sync.

Is there a way to do this with Mongo aggregate or query? So for each voting option I would get additional field like:

didIVoted: true

My Schema looks like this:

const SurveySchema = new Schema({
    title: {
        type: String
    },
    options: [{
        value: String,
        votes: [{ type: mongoose.Schema.Types.ObjectId, ref: 'User' }]
    }]
}, { timestamps: true })

mickl · Accepted Answer · 2019-03-12 17:55:35Z

1

You can use $addFields and $map to overwrite existing options field. To check if userId exists in votes array you can use $indexOfArray

SurveySchema.aggregate([
    {
        $addFields: {
            options: {
                $map: {
                    input: "$options",
                    in: {
                        value: "$$this.value",
                        votes: "$$this.votes",
                        didIVote: { $ne: [ { $indexOfArray: [ "$$this.votes", userId ] }, -1 ] }
                    }
                }
            }
        }
    }
])

answered Mar 12, 2019 at 17:55

mickl

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