Shift all elements of an array field to another array field throughout the whole collection

Working with Data
,
1

I have a collection with documents like the following (other fields excluded):

"array" : [
    ObjectId("..."),
    ObjectId("..."),
    ObjectId("...),
    ObjectId("...")
],
"anotherArray" : [ ],

I want all the documents to be updated to this:

"array" : [],
"anotherArray" : [ 
    ObjectId("..."),
    ObjectId("..."),
    ObjectId("...),
    ObjectId("...")
],

Is there a solution using aggregation or something simpler?

Note:

  1. All the documents have different number of elements.
  2. In each document, everything in the array needs to be shifted to anotherArray.
  3. All the documents need to be updated.
2

What have you tried so far?

What are the issues you faced?

Real documents would be better because we cannot cut-n-paste documents like

in our environment because the object ids are wrong.

3

I have two things in mind but am unable to figure out the syntax.

  1. Storing the array as a variable (let’s say temp), applying a { $pull : { array: true } } on array and doing a { $set: { anotherArray: temp } }.

  2. Using the $map to transform all the documents.

Here’s a document with some actual ObjectIds:

{
    "appliedProfiles" : [
        ObjectId("614f1e494d79516793413353"),
        ObjectId("613a4489c2fec521e5af8a4a"),
        ObjectId("613a08efc2fec521e5af8a18"),
        ObjectId("613a3fd4c2fec521e5af8a44")
    ],
    "selectedProfiles" : [],
}

Hope that makes things clearer.

4

I have not tested it but you could try:

{
  "$set" :
  {
     "selectedProfiles" : "$appliedProfiles" ,
     "appliedProfiles" : []
  }
}
5

Oh, well. That’s a lot simpler. Silly me.

All the selectedProfiles are not empty though so I think I need to try something like:

{
  "$addToSet": { selectedProfiles: { $each: "$appliedProfiles" } } 
  "$set" :  { "appliedProfiles" : []  }
}

Let me try it on a duplicate collection and get back to you.

1 Like
7

This gave me the following error:

The argument to $each in $addToSet must be an array but it was of type string

I did find this SO question: mongodb - Atomically move object by ID from one array to another in same document - Stack Overflow

But in my case there’s no conditional shifting but total shifting.

8

I solved it using a pipeline inside update command:

db.teamupparticipants.update(
    { },
    [{
        "$set": {
            selectedProfiles: {
                $map: {
                    input: "$appliedProfiles",
                    as: "profile",
                    in: "$$profile"
                }
            },
            appliedProfiles: []
        },
    }],
    { multi: true }
)

Make sure to include the update query inside an array so as to make it a pipeline.

1 Like
9

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