mongodb query

// Drop entire other collection
db.collection1.drop(); 

//rename collection field
db.posts.update({}, {$rename: {"usernmae": "username"}});

//Copy from one collection to another
db.collection1_backup.find().forEach(function(doc){
   db.collection1.insert(doc); // start to replace
});

//Update multiple records
db.news.update({},{$set : {"user":ObjectId("55d3fccf989b991500658f07")}},{multi:true}) 

//Add new field to collection
db.stream_radio.update({},{$set : {"active":true}},
                          {upsert:false,
                          multi:true});
//Add provider to user profile field if google-tokenId exist                          
db.users.update({"google-tokenId": { $exists: true } },{$set : {"profile.provider":"google"}},{multi:true}) 

//remove field
db.users.update({}, {$unset: {gender: 1}}, {multi: true})