Node.js/Mongoose wait for Async For-loop

Question

this is a bit of a beginners question. I need to query/find multiple elements from an array in my mongodb database. If at least one element pass an if-statement i want to set an error variable to true. Unfortunately because of the async call the variable will be returned early and remains false. Can you give me a hint on how to achieve this. Here is the code so far:

 objects = ["a","b","c"]
for (object of objects) {
    loanObject.findById(object._id)
        .then((object) => {
            if (object) {
                isError = true
            }

        })
        .catch(err => console.log(err))
}



console.log(isError) // returns false while should be true

alkhatim · Accepted Answer · 2021-08-16 20:13:37Z

use await and async, what you're currently doing is looping through your array, for each element you're firing a db call and telling it to set isError when it finishes but you're not waiting for it, so your code starts 3 db calls and then moves immediately to log isError which is false by default I guess in your code. When the db calls finish isError is being set to true but your code executed the console.log long before that.

Try this:

    for (object of objects) {
    const object = await loanObject.findById(object._id).catch(err => console.log(err));
    if (object) {
        isError = true;
    }
}

but a better solution is to use the mongoose $in operator so:

    const object = await loanObject.findOne({ _id: { $in: objects.map(object => object._id) } }).catch(err => console.log(err));
    if (object) {
      isError = true;
    }

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