Assistance with updating an array in MongoDB is required

I've come across a challenge with my document collection:

{
   _id: 1,
   name: 'xpto',
   arr: [1, 2, 3]
},
{
  _id: 2,
  name: 'xyz'
}

My goal is to add number 4 to the "arr" array using $addToSet and update {multi: 1}, but I encountered an error stating "Cannot apply $addToSet modifier to non-array." This error occurs because the second document does not have the "arr" field.

Is there a way to update an array using $push and/or $addToSet in all documents even if the array is not present in every one?

I attempted this using find, checking for cursor.arr and creating the array if it doesn't exist.

Do you know of any alternative approaches?

Answer №1

To easily add new elements to an array in the initial document, you can utilize the $push operator by executing the following command:

db.docs.update({_id:1},{$push:{arr:4}});

If you want to update both documents at once, you can also use the $push operator with an empty query object as the first parameter:

db.docs.update({}, {$push:{arr:4}});

The outcome will be: *{"_id":1, "arr":[1,2,3,4], "name":"xpto"} {"_id":2, "arr":[4], "name":"xyz"}*

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