I have a document like this

    {
      "_id": ObjectId("626f942bb092f78afd9dad9d"),
      "item_id": "external _id222",
      "metadata": {
        "item_name": "abc",
        "quantity": 123,
        "state": null
      },
    }

What I would like to do is, $inc i.e. increment the count of quantity and then update the state to SOLD, if quantity equals 124. I can do this by 2 queries, update quantity, do an if-else check and then update state. Is there a way to do this in one single query by update()? (preferably without aggregation)

CodePudding user response：

With MongoDB v4.2 , you can do this with a single update with an aggregation pipeline to achieve atomic behaviour. Use $add to do the increment and $cond to check for quantity = 123

db.collection.update({
  "item_id": "external _id222"
},
[
  {
    $set: {
      "metadata.quantity": {
        $add: [
          "$metadata.quantity",
          1
        ]
      }
    }
  },
  {
    $set: {
      "metadata.state": {
        $cond: {
          if: {
            $eq: [
              "$metadata.quantity",
              124
            ]
          },
          then: "SOLID",
          else: "$metadata.state"
        }
      }
    }
  }
],
{
  multi: true
})

Here is the Mongo playground for your reference.

CodePudding user response：

You can do this way

1. Check if quantity is 123
2. Then increment quantity and set state to SOLD

playground

db.collection.update({
  "metadata.quantity": 123
},
{
  "$inc": {
    "metadata.quantity": 1
  },
  "$set": {
    "metadata.state": "SOLD"
  }
},
{
  "multi": false,
  "upsert": false
})

Here, the trick is that you need to check the value which is before $inc operation.