About
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It is customary to ask for sample documents. While a schema is clear, it forces us to create our own documents to help you solve your problem. This is extra work that we won’t need to do when you provide sample documents.
The query parts is the same in both case so the index will be used to find the document. No matter how you do the update the resource intensive part is to find the document and then write back the document after the update. But if you find $map to intensive, you can avoid it by using a combination of $concatArrays and $slice using $indexOfArray to find where to $slice.