i have a document structure like this:

{
    "_id": "...",
    "shop": "pepe",
    "fruits": [
      {
        "name": "banana",
        "taste": "sweet",
      },
    ]
}

Now i want to change the type of fruits.taste to an array like this: "taste": ["sweet"]

So the result should be this:

{
    "_id": "...",
    "shop": "pepe",
    "fruits": [
      {
        "name": "banana",
        "taste": ["sweet"],
      },
    ]
}

i was trying to do that like this in a mongo playground query but that does not work:

db.getCollection('shops')
  .find()
  .forEach(function(document) {
   db.shops.update(
      { _id: document._id },
      { $set: { "document.fruits.$[].taste": [document.fruits.$.taste] } }
   );
})

How can i change in objects, which are in an array, a value from string to an array of string ?

Thanks for your help!

CodePudding user response：

Here's one way you could do it by using a pipeline in the update.

db.shops.update({
  "fruits.taste": {
    "$exists": true
  }
},
[
  {
    "$set": {
      "fruits": {
        "$map": {
          "input": "$fruits",
          "as": "fruit",
          "in": {
            "$mergeObjects": [
              "$$fruit",
              {"taste": ["$$fruit.taste"]}
            ]
          }
        }
      }
    }
  }
],
{"multi": true}
)

Try it on mongoplayground.net.

CodePudding user response：

Query

• you need to refer to an existing field, and use $taste so you need a pipeline update
• map on fruts, and put the taste value inside []

Playmongo

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