Question 117885 in Mongodb Question posted in
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Mongodb Update a field in a document and then update another depending on the value of previous field

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)

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2

Answers


  1. 0

    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.

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  2. 0

    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.

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