Database
[{owner:"10",friends:[{friendId:1,isFromFacebook:false,thisFriendReceivedGiftTimeStamp:null,thisFriendSentGiftTimeStamp:null},{friendId:2,isFromFacebook:false,thisFriendReceivedGiftTimeStamp:null,thisFriendSentGiftTimeStamp:null},{friendId:3,isFromFacebook:false,thisFriendReceivedGiftTimeStamp:null,thisFriendSentGiftTimeStamp:null},{friendId:4,isFromFacebook:false,thisFriendReceivedGiftTimeStamp:null,thisFriendSentGiftTimeStamp:null},{friendId:5,isFromFacebook:false,thisFriendReceivedGiftTimeStamp:null,thisFriendSentGiftTimeStamp:null}]}]
Query
db.collection.update({},{"$set":{"friends.$[x].thisFriendReceivedGiftTimeStamp":new Date()}},{"arrayFilters":[{"x.friendId":{$in:[1,3,5]}}],"multi":true})