创建数据库视图

Room 持久性库 2.1.0 及更高版本支持 SQLite 数据库视图，可让您将查询封装到类中。Room 将这些由查询支持的类称为 视图，它们在 DAO 中使用时与简单数据对象 behave 相同。

创建视图

如需创建视图，请为类添加 @DatabaseView 注解。将该注解的值设置为此类应表示的查询。

以下代码段提供了视图的示例

Kotlin

@DatabaseView("SELECT user.id, user.name, user.departmentId," +
        "department.name AS departmentName FROM user " +
        "INNER JOIN department ON user.departmentId = department.id")
data class UserDetail(
    val id: Long,
    val name: String?,
    val departmentId: Long,
    val departmentName: String?
)

Java

@DatabaseView("SELECT user.id, user.name, user.departmentId," +
              "department.name AS departmentName FROM user " +
              "INNER JOIN department ON user.departmentId = department.id")
public class UserDetail {
    public long id;
    public String name;
    public long departmentId;
    public String departmentName;
}

将视图与数据库关联

如需将此视图作为应用数据库的一部分包含在内，请在应用的 @Database 注解中包含 views 属性

Kotlin

@Database(entities = [User::class],
          views =[UserDetail::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao
}

Java

@Database(entities = {User.class}, views = {UserDetail.class},
          version = 1)
public abstract class AppDatabase extends RoomDatabase {
    public abstract UserDao userDao();
}
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