title: Mongodb findoneandupdate with aggregation pipeline
body: <p>I have a data in MongoDB like this</p>
  
  <pre><code>    {"_id":{"$oid":"5ec4ed0b94996124187b95ce"},
             "cid":"245345323",
       "dtl":[
            {"_id":{"$oid":"5ed5ab655df7930ec424be1e"},
                "sid":"test",
                "amt":{"$numberInt":"48"},
                "Name":"test"},
            {"_id":{"$oid":"5ed5ac9f79a75423d4bc0270"},
               "sid":"s",
               "amt":{"$numberInt":"14"},
               "Name":"sfds"},
            {"_id":{"$oid":"5ed5ace7d204ab144863ed7a"},
               "sid":"wesad",
               "amt":{"$numberInt":"6"},
               "Name":"2sdad"
            },
          "updated":{"$date":{"$numberLong":"1589964043787"}},
          "__v":{"$numberInt":"6"},
         "TotalAmt":{"$numberInt":"68"}}
  </code></pre>
  
  <p>I need to update the TotalAmt field only if amt field in the array has value greater than 10. I have used the below 2 options</p>
  
  <pre><code>PM.findOneAndUpdate(
        {
          _id: MongoId,
        },
        [
          {
            $set: {
              //TotalAmt: { $sum: '$dtl.amt' },
              /*TotalAmt: {
                $cond: {
                  if: { $gte: ['$dtl.amt', 10] },
                  then: { $sum: '$dtl.amt' },
                  else: 0,
                },
              },*/
            },
          },
        ],
        { new: true }
      )
  </code></pre>
  
  <p>It works fine without amt > 10 condition (first option commented).  But not working if I add the condition. Any help would be appreciated. Thanks </p>