[{"Employee":[{"empeId":"e001","fName":"James","lName":"Bond","email":"jamesbond@hotmail.com","experience":["Database Design","SQL","Java"]},{"empeId":"e002","fName":"Harry","lName":"Potter","experience":["Data Warehouse","SQL","Spark Scala","Java Scripts"]}],"Project":[{"projectId":"p001","projectTitle":"Install MongoDB"},{"projectId":"p002","projectTitle":"Install Oracle"},{"projectId":"p003","projectTitle":"Install Hadoop"}],"EmployeeProject":[{"empeId":"e001","projectId":"p001","hoursWorked":4},{"empeId":"e001","projectId":"p003","hoursWorked":2},{"empeId":"e002","projectId":"p003","hoursWorked":5}]}]

db.collection.update({},[{$set:{"Employee":{$map:{input:"$Employee",as:"m",in:{$cond:[{$eq:["$$m.empeId","e001"]},{$mergeObjects:["$$m",{experience:{$concatArrays:["$$m.experience",["test"]]}}]},"$$m"]}}}}}])