mongodb update the last array element

Question

the following documents:

{
    "_id": ObjectId("5d648b0d5aeada5177bb54e4"),
    "time": [{
            "start": "2019/8/25 9:59:30",
            "end": "2019/8/25 10:59:30"
        },
        {
            "start": "2019/8/26 9:59:30",
            "end": "2019/8/26 10:59:30"
        },
        {
            "start": "2019/8/27 9:59:30",
            "end": "2019/8/26 9:59:30"
        }
    ]
}

How to update the last element in array?

I'm already tried:

db.document.update(
  {
    "_id": ObjectId("5d648b0d5aeada5177bb54e4")
  }, 
  {
    $set: {
        "time.-1.end": "2019/8/26 10:59:30"
    }
  }
)

but it does not work...

Answer 1

it is very simple. get the last element's index/position.

var data = {
"_id" : "5d648b0d5aeada5177bb54e4",
"time" : [ 
    {
        "start" : "2019/8/25 9:59:30",
        "end" : "2019/8/25 10:59:30"
    }, 
    {
        "start" : "2019/8/26 9:59:30",
        "end" : "2019/8/26 10:59:30"
    }, 
    {
        "start" : "2019/8/27 9:59:30",
        "end" : "2019/8/26 9:59:30"
    }
]
}

var len = data.time.length - 1;
var objUpdate = {};
var updateQuery = "time." + len + ".end";
objUpdate[updateQuery] = "2019/8/26 11:59:30";

db.getCollection('test').update({"_id" : ObjectId("5d648b0d5aeada5177bb54e4")}, {$set:objUpdate});

Answer 2

Filter out the document using time.start field:

Try the below query:

db.arraytest.updateOne({"_id" : ObjectId("5d648b0d5aeada5177bb54e4"), "time.start" : "2019/8/27 9:59:30"},
{$set: { "time.$.end": "2019/8/26 10:59:30" }})