mongodb 中的条件 findoneandupdate

Question

I need to increment the counter field as long as it's less than 500 otherwise reset the counter to zero.

Here is my snippet:

StudentInfo.findOneAndUpdate(
    { studId: SID },
    **{ $inc: { counter: 1 } },**
    (err, studInfo) => {
        if (err || !studInfo) {
            console.log(err);
        } else {
            console.log(${JSON.stringify(studInfo));
        }
    },
);

How can I do it in a single update call?

Answer 1

You can do it with Aggregation framework:

• $cond with $lt - To check if the current value of the counter is less than 500
• $sum - To increase the current value of the counter by 1 if the condition is true

db.collection.update({
  "key": 1
},
[
  {
    "$set": {
      "counter": {
        $cond: {
          if: {
            $lt: [
              "$counter",
              500
            ]
          },
          then: {
            $sum: [
              "$counter",
              1
            ]
          },
          else: 0
        }
      }
    }
  }
],
{
  "multi": false,
  "upsert": false
})

Working example