How to use parameter fields in Room @Query?

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