Update element of an array using aggregation pipeline in `update` operation

Question

Scenario

For the below document, I want to update the status of a specific message in the messages array:

[{
    "_id" : ObjectId("6079bab4f297df39a44609cb"),
    "title" : "Test messages of single user",
    "messages" : [ 
        {
            "_id" : ObjectId("6079bab4f297df39a44609cc"),
            "body" : "Test 1",
            "status" : 1
        }, 
        {
            "_id" : ObjectId("6079bab4f297df39a44609cd"),
            "body" : "Test 2",
            "status" : 1
        }, 
        {
            "_id" : ObjectId("6079bcf7c041b00ec4cebb9d"),
            "body" : "Hello I'm Sam",
            "status" : 1
        }
    ]
}]

Query without aggregation pipeline in update operation updates the status in single message.

Run below query here

db.update(
  { 
    "_id": ObjectId("6079bab4f297df39a44609cb"), 
    "messages": { $elemMatch: { _id: ObjectId("6079bcf7c041b00ec4cebb9d") } }
  }, 
  {
    $set: { "messages.$.status": 2 }
  }
)

Query with aggregation pipeline in update operation updates the status in all messages

Run below query here

db.update(
  { 
    "_id": ObjectId("6079bab4f297df39a44609cb"), 
    "messages": { $elemMatch: { _id: ObjectId("6079bcf7c041b00ec4cebb9d") } }
  }, 
  [
    {
      $set: { "messages.status": 2 }
    }
  ]
)

MongoDB Version: 4.4

Note: For some reason, I need to use the second query but I am not able to update the status of single message. It always update all the messages

Question

Why is the second query updating status in all messages when I've selected the message that I want to update?
How can I update status of single message with aggregation pipeline (second query)?

It'll be helpful if you can share link for the query

Tushar Gupta - curioustushar · Accepted Answer · 2021-04-19 13:55:00Z

10

Demo - https://mongoplayground.net/p/VZHes8--O5O

Use $[]

The filtered positional operator $[] identifies the array elements that match the arrayFilters conditions for an update operation

db.collection.update(
 { "_id": ObjectId("6079bab4f297df39a44609cb") },
 { $set: { "messages.$[m].status": 2 } },
 { arrayFilters: [ { "m._id": ObjectId("6079bcf7c041b00ec4cebb9d") } ]
})

Update

Demo - https://mongoplayground.net/p/GyBxksYKpmf

Use $map

db.collection.update({
  "_id": ObjectId("6079bab4f297df39a44609cb"),
  "messages": {
    $elemMatch: {
      _id: ObjectId("6079bcf7c041b00ec4cebb9d")
    }
  }
},
[
  {
    $set: {
      "messages": {
        $map: {
          input: "$messages",
          as: "m",
          in: {
            $cond: [
              { $eq: [ "$$m._id", ObjectId("6079bcf7c041b00ec4cebb9d") ] }, // condition
              { $mergeObjects: [ "$$m", { status: 2 } ] }, // true
              "$$m" // false
            ]
          }
        }
      }
    }
  }
])

$cond

$mergeObjects

Note- it's overkill in this case

edited Apr 19, 2021 at 13:55

answered Apr 19, 2021 at 13:31

Tushar Gupta - curioustushar

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7 Comments

Abhishek Pankar Over a year ago

I need to use the aggregation pipeline in update operation. Just like I mentioned in second query

Abhishek Pankar Over a year ago

What do you mean by overkill? Can you please explain?

Tushar Gupta - curioustushar Over a year ago

@AbhishekPankar suppose I've 1000s messages $map will loop over every message and check condition.

Robert Over a year ago

Not far from witchcraft... but works for me! MongoDB is so great in many ways. Less great in others.

Gabriel Mochi Over a year ago

finally the answer!! I was searching for it for so many days

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