Android使用Room操作數據庫流程詳解

更新時間：2022年11月17日 09:59:52 作者：Flynn_MIMD

谷歌推薦使用Room操作數據庫，Room在 SQLite 上提供了一個抽象層，在充分利用 SQLite強大功能的同時，能夠流暢地訪問數據庫

dependencies {
def room_version = "2.4.3"

implementation "android.arch.persistence.room:runtime:$room_version"
annotationProcessor "android.arch.persistence.room:compiler:$room_version"

implementation "android.arch.persistence.room:rxjava2:$room_version"

testImplementation "android.arch.persistence.room:testing:$room_version"
}

1. 創(chuàng)建實體類User

@Entity(tableName = "users")
public class User {
    @PrimaryKey
    public int uid;
    @ColumnInfo(name = "first_name")
    public String firstName;
    @ColumnInfo(name = "last_name")
    public String lastName;
}

@Entity實體類，users表的名稱，不加默認user

@ColumnInfo列名

@PrimaryKey主鍵

2. 創(chuàng)建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(onConflict = OnConflictStrategy.REPLACE)
    void insertAll(User... users);
    @Delete
    void delete(User user);
}

增，刪，改：將實例與表的主鍵進行匹配

查詢結果將自動映射到對應類型的字段，若未映射將報警告

3. 數據庫

抽象類AppDatabase 定義數據庫配置，并作為應用對持久性數據的主要訪問點，擴展了RommDataBase

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

4. 使用

AppDataBase db = Room.databaseBuilder(getApplicationContext(),
                        AppDataBase.class, "database-name").build();
                for (int i = 0; i < 10; i++) {
                    User user = new User();
                    user.uid = i;
                    user.firstName = "Shell" + i;
                    user.lastName = "Hub" + i;
                    db.userDao().insertAll( user);
                    List<User> userList = db.userDao().getAll();
                    for(User user1 : userList) {
                        Log.d("mip",""+user1.firstName);
                    }
                }

為了節(jié)約獲取數據庫的時間和資源，采取單例模式

簡單實現：

public class Utils {
    private static AppDataBase db = null;
    private static Context context = null;
    public static AppDataBase getDb(){
        if( db == null) {
            db = Room.databaseBuilder(context,
                    AppDataBase.class, "database-name").build();
        }
        return db;
    }
    public static void setContext(Context context){
        Utils.context = context;
    }
}

調用

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Utils.setContext(getApplicationContext());
        new Thread(new Runnable() {
            @Override
            public void run() {
                AppDataBase db = Utils.getDb();
                for (int i = 0; i < 10; i++) {
                    User user = new User();
                    user.uid = i;
                    user.firstName = "Shell" + i;
                    user.lastName = "Hub" + i;
                    db.userDao().insertAll( user);
                    List<User> userList = db.userDao().getAll();
                    for(User user1 : userList) {
                        Log.d("mip",""+user1.firstName);
                    }
                }
            }
        }).start();
    }
}

路過的大佬們有更好的單例實現請告訴我一下，

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