How to update the value of array object property with another filed value of the same array object in MongoDB

Question

In the below restaurant object, I would like to update the addons property of the optionalAddons object with the value of addableIngredients. How can I do so for each restaurant and each item?

  "name": "4Cheeze",
  "items": [
    {
      "name": "Chicken Grill",
      "addableIngredients": "cheese - 2, mayo - 0",
      "optionalAddons": {
        "addable": 10,
        "addons": ''
      }
    },
    {
      "name": "Fried Momo",
      "addableIngredients": "cheese - 2, mayo - 0",
      "optionalAddons": {
        "addable": 10,
        "addons": ''
      }
    },
  ],
}

Here is the Mongo playground link to play with: https://mongoplayground.net/p/JVjV2AiocHD

Answer 1

One option is to use an update with a pipeline to push the current value of addableIngredients into the existing array:

db.collection.updateMany({},
[
  {$set: {items: {$map: {
          input: "$items",
          in: {$mergeObjects: [
              "$$this",
              {optionalAddons: {addons: {
                    $mergeObjects: [
                      "$$this.optionalAddons",
                      {addons: {$concatArrays: [
                            "$$this.optionalAddons.addons",
                            ["$$this.addableIngredients"]
                       ]}}
                    ]
              }}}
          ]}
  }}}}
])

See how it works on the playground example