MongoDB how to change field type in array from string to array and keep original value

Question

Image of original document

I have db "test" with collection "testing". In that collection I have document with array called "methods" which contains object 0(and maybe lot more objects 1,2,3,4...). Inside those objects I have string field "tool" with tool "xray". I want that string field "tool" to be array of tools. I found command to change tool field to array with:

db.testing.update(
  {},
  [{ $set: { "methods.tool": ["$methods.tool"] } }],
  { multi: true }
)

This works but it creates one extra array "0:Array" and I dont want that

Outcome

I want the end result look like this: end result

Answer 1

Query

• $map to update all document members of methods
• $$this is the current member each time
• $mergeObjects is used to add the updated field, were tool:xray becomes tool: [xray]

*paths that the field is part of array, they are arrays also, "$methods.tool" is an array of all the tools in all methods.

Test code here

update(
{},
[{"$set": 
    {"methods": 
      {"$map": 
        {"input": "$methods",
          "in": {"$mergeObjects": ["$$this", {"tool": ["$$this.tool"]}]}}}}}],
{"multi": true})