I'm trying to make a seemingly simple update to a MongoDB collection that looks like the below using Node.

Collection

{
  account_id: "ORG1",
  progress: [{week: 1, goal: 5000, raised: 2400}, {week: 2, goal:5100,  raised: 1000}]
} 

The goal is to be able to

1. Find the correct org (this works for me)
2. Add a value to the last array entry's "raised" value. (e.g. Initially the raised value is 1000, after my update, it will be 1000 an incoming value).

My hacky approach would be to do a find query to get the initial value and then do an update to add my incoming value to the initial value. But I'm sure there's a simpler way.

Thanks in advance!

CodePudding user response：

One option is using an update pipeline:

1. Split the array into the last item and all the rest.
2. update the last item
3. Build the array again using $concatArrays

db.collection.update(
  {account_id: "ORG1"},
  [
    {$set: {
      lastItem: {$last: "$progress"},
      rest: {$slice: ["$progress", 0, {$subtract: [{$size: "$progress"}, 1]}]}
    }
    },
    {$set: {"lastItem.raised": {$add: ["$lastItem.raised", incomingValue]}}},
    {$set: {
      progress: {$concatArrays: ["$rest", ["$lastItem"]]},
      lastItem: "$$REMOVE",
      rest: "$$REMOVE"
    }
  }
])

See how it works on the playground example - concatArrays

Another option is using $reduce:

Here we are iterating on the array, for each item checking if it is the last one, and if so updating it:

db.collection.update(
  {account_id: "ORG1"},
  [
  {$set: {lastIndex: {$subtract: [{$size: "$progress"}, 1]}}},
  {$set: {
      lastIndex: "$$REMOVE",
      progress: {
        $reduce: {
          input: "$progress",
          initialValue: [],
          in: {
            $concatArrays: [
              "$$value",
              [
                {
                  $cond: [
                    {$eq: [{$size: "$$value"}, "$lastIndex"]},
                    {$mergeObjects: [
                       "$$this",
                        {raised: {$add: ["$$this.raised", incomingValue]}}
                      ]
                    },
                    "$$this"
                  ]
                }
              ]
            ]
          }
        }
      }
    }
  }
])

See how it works on the playground example - reduce

CodePudding user response：

One way to do it is by using "$function" in the update/aggregation pipeline.

db.collection.update({
  "account_id": "ORG1"
},
[
  {
    "$set": {
      "progress": {
        "$function": {           // your increment value goes here ⮯
          "body": "function(prog) {prog[prog.length - 1].raised  = 75; return prog}",
          "args": ["$progress"],
          "lang": "js"
        }
      }
    }
  }
])

Try it on mongoplayground.net.