MongoDb push only if property not already in array

Question

I'm trying to update a nested array in a document only if the array does not already include the item like so:

await userCollection.findOneAndUpdate(
    { _id: ObjectId('616acc597ebda90ca6ffee21') },
    {
      'devices': {
        $push: {
          $cond: {
            if: {
              $in: [req.body.serial, '$devices']
            },
            then: '$devices',
            else: { serial: req.body.serial, data: [] }
          }
        }
      }
    },
    { returnOriginal: false },
    (err, _) => {
      if (err) {
        return res.status(400);
      } else {
        return res.status(200).json(user.value);
      }
    }
  );

This is my user object:

{
    "_id": "616acc597ebda90ca6ffee21",
    "username": "test@test.com",
    "displayName": "Test",
    "devices": [
      {
        "serial": "865674036421275",
        "data": [
          {
            "timestamp": "2021-10-16T12:36:35.799Z"
          },
          {            
            "timestamp": "2021-10-16T12:41:33.633Z"
          },
          {           
            "timestamp": "2021-10-16T12:52:03.055Z"
          }
        ]
      },
      
    ],
    "hashedPassword": "R5vt3vY7vEvTHvhC7YGNOWuIjBUQGLqsd92QGE06tjU=",
    "salt": "6RS0OVIFboCkIEPHdZmTcQ==",
    "dateCreated": "2021-10-16T12:58:00.294Z"
  }

How will I check if serial is already in devices? Also, is it possible to throw an error if it already exists?

user_4882692 · Answer

Query

find to update only documents that dont have this serial
(with eq/ne query operators, we can do arrays=value, if array has the value its true)
replace the "000" with the serial you want to add
push in the end
updateOne will return the result, and you can see if update is done or not, see your driver method details.

*it will be fast, and you dont need an index on devices.serial because it selects a specific document already with the _id match

Test code here

db.collection.update({
  "_id": ObjectId("616acc597ebda90ca6ffee21"),
  "devices.serial": {
    "$ne": "000"
  }
},
{
  "$push": {
    "devices": {
      "serial": "000",
      "data": []
    }
  }
})

We cant mix update operators with aggregate operators. $cond is aggregate operator, it cant be mixed with $push update operator. (aggregate $push is for group, cant add to an array)

We can do the update with update pipeline, but here a normal update is simpler.

user_4049025 · Answer

There's an update operator called addToSet check it here

user_5467132 · Answer

MongoDB Raw Query

db.userCollection.updateOne({
    _id: ObjectId('616acc597ebda90ca6ffee21'), // Object Id, make sure It is Object Id only else match just string version
    "devices.serial": {$ne: "SerialNeedToMatch" }
}, {
    $push: {
        "devices": {
            serial: '111' // or complete object 
        }
    }
})

MongoDb push only if property not already in array

3 Answers