CODEWITHSUNDEEP
mongodbmongodb-query
devdre
devdre

Reputation: 53

MongoDB: How to update field of array element depending on other field?

I am trying to update data in my MongoDB (4.2) by using update with a pipeline. The difficulty is that I want to add a field to an array element depending on another field. Also I want to do this for each element. I know I could do by Javascript for each but I was wondering if there is a better way. So this is what I want to do as an example

Before:

{
    "_id" : ObjectId("555555555"),
    "messages" : [
        {
            "author" : {
                "userId" : "12345",
                "name" : "John"
            },
            "text" : "Any text",
        },
        {
            "author" : {
                "userId" : "56789",
                "name" : "Jim"
            },
            "text" : "also text"
        }
    ]
}

After

{
    "_id" : ObjectId("555555555"),
    "messages" : [
        {
            "author" : {
                "userId" : "12345",
                "name" : "John",
                "newId" : "00012345"
            },
            "text" : "Any text",
        },
        {
            "author" : {
                "userId" : "56789",
                "name" : "Jim",
                "newId" : "00056789"
            },
            "text" : "also text"
        }
    ]
}

What I tried:

db.mail.update(
   {"_id" : ObjectId("555555555")},
  [{ $set: { "messages.$[].author.newId": { $concat: [ "000", "$messages.$[].author.userId"]}}}],
  { multi: true, writeConcern: {w: 0} }
)

Does anybody know how to solve this? Thank you

Upvotes: 3

Views: 772

Answers (1)

prasad_
prasad_

Reputation: 14287

This will do the required update.

db.test.update(
  { _id : ObjectId("555555555") },
  [ 
    { 
      $set: { 
          messages: {
              $map: {
                   input: "$messages",
                   in: {
                       $mergeObjects: [
                           "$$this",
                           { "author": { 
                                  $mergeObjects: [ 
                                       "$$this.author", 
                                       { newId: { $concat: [ "000", "$$this.author.userId"] } } 
                                   ]
                           } }
                       ]
                   }
              } 
          }
      }
    }
  ],
  { multi: true, writeConcern: {w: 0} }
)

Note that the all positional operator $[] for array updates is to be used with update operations when not using the aggregation. You have to use aggregation to update when a field value depends upon another field in the document.

Upvotes: 3

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