How to use parameter fields in Room @Query?

You can't pass parameters like that to room. It does not support a full expression language. You have to use primitive types to pass parameters. Like this,

@Query("SELECT * FROM ticket where user_id = :user_id")
LiveData<Ticket> loadFromUser(String user_id);

A simple solution is to create two other functions, one is for user_id and one is for user as follows:

@Query("SELECT * FROM ticket where user_id = :user_id")
LiveData<Ticket> loadFromUser(String user_id);

@Transaction
LiveData<Ticket> loadFromUser(User user){
   return loadFromUser(user.id);
}