问题
I have a User class with a field id, so I wanted to run the following query with Room:
@Query("SELECT * FROM ticket where user_id = :user.id")
LiveData<Ticket> loadFromUser(User user);
But I am getting error marks on Android Studio on user.id and all examples I find online only use the direct parameter of the @Query method, usually a String or an int.
Is it possible to use an object's field in a Room @Query? If positive, so what's the proper way of referencing it.
回答1:
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);
回答2:
in my case i used @RawQuery
in DAO you can write
@RawQuery
LiveData<Ticket> loadFromUser(SupportSQLiteQuery query);
and create your query and pass to it.
SimpleSQLiteQuery query = new SimpleSQLiteQuery("SELECT * FROM ticket where user_id = ?") , new Object[]{user.id})
and pass this query to DAO method.
userDao.loadFromUser(query)
来源：https://stackoverflow.com/questions/51851243/how-to-use-parameter-fields-in-room-query