要使用Android Room的@Embedded和@Relation注解,需要按照以下步骤进行设置:
build.gradle
文件中的dependencies块中添加以下依赖项:implementation 'androidx.room:room-runtime:2.2.6' // Room核心库
annotationProcessor 'androidx.room:room-compiler:2.2.6' // Room注解处理器
@Entity
public class User {
@PrimaryKey
public int userId;
public String name;
}
@Entity
public class Address {
@PrimaryKey
public int addressId;
public int userId;
public String street;
public String city;
}
public class UserWithAddresses {
@Embedded
public User user;
@Relation(parentColumn = "userId", entityColumn = "userId")
public List addresses;
}
@Dao
public interface UserDao {
@Query("SELECT * FROM User")
List getUsersWithAddresses();
}
@Database(entities = {User.class, Address.class}, version = 1)
public abstract class MyAppDatabase extends RoomDatabase {
public abstract UserDao userDao();
private static volatile MyAppDatabase INSTANCE;
public static MyAppDatabase getDatabase(final Context context) {
if (INSTANCE == null) {
synchronized (MyAppDatabase.class) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
MyAppDatabase.class, "my_database")
.build();
}
}
}
return INSTANCE;
}
}
MyAppDatabase db = MyAppDatabase.getDatabase(this);
UserDao userDao = db.userDao();
List usersWithAddresses = userDao.getUsersWithAddresses();
for (UserWithAddresses userWithAddresses : usersWithAddresses) {
User user = userWithAddresses.user;
List addresses = userWithAddresses.addresses;
// 处理用户和地址数据
}
这样,您就可以使用@Embedded和@Relation注解在Android Room中获取关联数据了。注意,以上代码示例仅供参考,您可能需要根据自己的实际需求进行适当的修改和调整。