db.getCollection('users').update( {"token.token":"21jpjg7pqdtigsdektmndqkobthdcktg"}, {$push:{accounts:"test"}} ) i run the command above in order to create an array field and the first element inside will be test but i get the error The field 'accounts' must be an array but is of type NULL in document i am really confused if i have to create a schema beforehand whats the point of using mongodb over some sql database i am using in Memory engine