How to remove a field having a specified value from a MongoDB document?

Question

Here is a given document in mongo db as below

{

"emailid": "xxx.gmail",

"user_devices": [],
"devices": [{
    "created_time": 1607153351,
    "token": 123
},
{
    "created_time": 1807153371,
    "token": 1345
}]

}

Here i want to remove the field inside devices ie "created_time": '', "token": '1345' here token value is known, so need to delete "created_time" along with "token" where output is like

{

"emailid": "xxx.gmail",

"user_devices": [],
"devices": [{
    "created_time": 1607153351,
    "token": 123
}]

}

I tried unset code like below

var myquery = { 'emailid': emailid , 'devices.token':1345};
        var newvalues = { $unset:{
        'devices.created_time':'',
        'devices.token':1345
        } };

and used 

updateOne(myquery, newvalues, function(err, res))

but it does not work. Can anyone tell how to remove this specified field. Thanks in advance.

Answer 1

Since the object you want to remove is in an array, you have to use $pull in this way:

db.collection.update({
  "emailid": "xxx.gmail"
},
{
  "$pull": {
    "devices": {
      "token": 123
    }
  }
})

In this query you are telling mongo: "Remove -using $pull- one field from the array devices where token is 123".

Example here

Edit:

Also, if you want to remove only one field into objec within array and not the object itself, the you can use $[<identifier>] to filter and then $unset like this:

db.collection.update({
  "emailid": "xxx.gmail"
},
{
  "$unset": {
    "devices.$[elem].created_time": ""
  }
},
{
  "arrayFilters": [
    {
      "elem.token": 123
    }
  ]
})

In this query, using arrayFilters you can $unset only in the object where token is 123. You can use created_time to filter if you want too.

Example here