MongoDB findOneAndUpdate for value less than other value


I can’t seem to figure out the right syntax to update (increment) a value by 1 if one value is smaller than another. Here’s some more details:

Data Structure

    "currentTask": 0,

What I want to do

  1. If there is a document where currentTask < maximumTask
  2. Retrieve that document
  3. Increment the currentTask value by 1

What I tried

let solver = await solvers.findOneAndUpdate({"currentTask":{"$lt": "$maximumTask"}},{"$inc":{"currentTask":1}});

I feel like I’m quite close but obviously new to MongoDB! Any help would be much appreciated 🙂


The syntax you use is for comparing a value that is on the document to an input value (which is not saved on the document). If you want to compare two values from the document, use $expr:

  $expr: {
    $lt: [
  $inc: {
    currentTask: 1

Playground example

This answer will return the document before the update. To get the document after the update, use the options like this:

{$expr: {$lt: ["$currentTask", "$maximumTask"]}},
{$inc: {currentTask: 1}},
{returnNewDocument: 1})

Answered By – nimrod serok

Answer Checked By – Marie Seifert (AngularFixing Admin)

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