[{isPrivate:false,message:"My name is stark",gender:"unisex",age:"19",createdBy:ObjectId("abcff9ef71fa048cea3c8a97")},{isPrivate:false,message:"My name is james",gender:"unisex",age:"20",createdBy:ObjectId("defff9ef71fa048cea3c8a97")},{isPrivate:false,message:"My name is harry",gender:"unisex",age:"20",createdBy:ObjectId("defff9ef71fa048cea3c8a97")},{isPrivate:false,message:"My name is max",gender:"unisex",age:"20",createdBy:ObjectId("abcff9ef71fa048cea3c8a97")}]

db.collection.aggregate([{$project:{isPrivate:1,message:1,gender:1,age:1,matchResult:{$regexMatch:{input:{$toString:"$createdBy"},regex:"abcff9ef71fa048cea3c8a97"}}}},{$sort:{matchResult:-1}}])