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How do I update this document value in Mongoose? .findOne and then .save() isn't working

November 27, 2021

I have a .put route on my Express server that is supposed to allow the user to vote in a poll, incrementing its total votes by 1.

My expectation from using both .findOne and then doc.save() and .findOneAndUpdate is that my document is successfully updated after I increment the poll object’s value by 1 in the label.

Here is my code:

router.put("/vote", async (req, res) => {
    // let username = req.body.username;
    let pollId = req.body.pollId;
    let voteTarget = req.body.voteTarget; // is values like "mango" "pineapple"

    const filter = { pollId: pollId };

    let pollToUpdate = await Poll.findOne(filter);
    let pollOptions = pollToUpdate.options;

    let newPollValue;
    for (let i = 0; i < pollToUpdate.options.length; i++) {
        if (pollOptions[i].label === voteTarget) {
            let currentVoteTargetValue = pollOptions[i].votes;
            newPollValue = currentVoteTargetValue + 1;
            pollOptions[i].votes = newPollValue;
        }
    }
    await pollToUpdate.save();
    res.status(200).send(
        "successfully updated poll value for " +
            voteTarget +
            " to value " +
            newPollValue
    );

As you can see, I have my votes set into the Poll document like this:

options: Array
0: Object
label: "apples"
votes: 0
1: Object
label: "oranges"
votes: 0
2: Object
label: "pineapple"
votes: 0
3: Object
label: "mango"
votes: 0

That is how it looks in the MongoDB database. That is just its field. It is inside of a bigger doc.

This MongoDB documentation page claims I can use doc.save() to accomplish my goal. It doesn’t work, sending Postman requests to increment the poll over and over don’t work.

This other mongodb doc page claims I can use findOneAndUpdate(filter, update) to accomplish my goal. It doesn’t work, the request to +1 to the vote field doesn’t work.

Specifically I am sending this Postmanr equest over and over:

//put route
http://127.0.0.1:8080/api/poll/vote

// body
{
    "username": "crono",
    "pollId": "tr7b1sli6ufo5no0",
    "voteTarget": "pineapple"
}

edit:

Even doing

let newOptions = [...oldOptions];

updateTarget.options = newOptions;
console.log(updateTarget.options, 141);
await updateTarget.save();

does increment the future value of the document as i expect. The console.log statement states that the votes for "pineapple" are 1 and not the 0 it loaded with. I then call await updateTarget.save() which really ought to commit my changes to the database. And yet the next rendition of Postman making a request sets me back at 0. I’m baffled.