Android 數據存儲 Room

原本想查一下Android最新的數據存儲知識，意外發現：官方推薦使用Room代替SQLite，那就學習一下把。

Room由三部分組成

1. Database

2. Entity

3. DAO

安裝

詳見這裏

Database

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

Entity

@Entity
public class User {
    @PrimaryKey
    public int uid;

    @ColumnInfo(name = "first_name")
    public String firstName;

    @ColumnInfo(name = "last_name")
    public String lastName;
}

DAO

@Dao
public interface UserDao {
    @Query("SELECT * FROM user")
    List<User> getAll();

    @Query("SELECT * FROM user WHERE uid IN (:userIds)")
    List<User> loadAllByIds(int[] userIds);

    @Query("SELECT * FROM user WHERE first_name LIKE :first AND " +
           "last_name LIKE :last LIMIT 1")
    User findByName(String first, String last);

    @Insert
    void insertAll(User... users);

    @Delete
    void delete(User user);
}

使用

AppDatabase db = Room.databaseBuilder(getApplicationContext(),
        AppDatabase.class, "database-name").build();

下面是官方提到的注意事項:

Note: If your app runs in a single process, you should follow the singleton design pattern when instantiating an AppDatabase object. Each RoomDatabase instance is fairly expensive, and you rarely need access to multiple instances within a single process.

If your app runs in multiple processes, include enableMultiInstanceInvalidation() in your database builder invocation. That way, when you have an instance of AppDatabase in each process, you can invalidate the shared database file in one process, and this invalidation automatically propagates to the instances of AppDatabase within other processes.

參考文獻：

• Save data in a local database using Room
• Android Room with a view（須要藉助代理）
• Android Persistence（須要藉助代理）
• Android Architecture Components
• Save data using SQLite
• Android Sunflower