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Android官方ORM資料庫Room技術解決方案:@Embedded內嵌對象(二)
(一)附錄1簡介了Android Room的基本使用。在附錄1例子中,User對象元素均為普通的Java基礎資料型別 (Elementary Data Type),但是實際的開發中,通常建立的持久化儲存物件複雜,且通常是結構化的Java對象,互相之間存在引用或者內嵌關係。
Android Room支援資料庫表Java對象通過註解符@Embedded內嵌一個Java對象。這樣就像過去的ORM資料庫一樣,比如構造一個名為Info的Java對象,作為一個成員變數添加到User裡面:
package zhangphil.demo;import android.arch.persistence.room.ColumnInfo;import android.arch.persistence.room.Embedded;import android.arch.persistence.room.Entity;import android.arch.persistence.room.PrimaryKey;/** * Created by Phil on 2017/11/22. */@Entity(tableName = "user_table")public class User { @PrimaryKey(autoGenerate = true) public int userId; @ColumnInfo(name = "userName") public String name; @ColumnInfo(name = "userAge") public int age; @ColumnInfo(name = "updateTime") public long updateTime; @Embedded public Info info;}
(二)Info對象本身也是一個Android Room的@Entity。也有自己的列名和主鍵等完整的Android Room資料表要素,Info.java:
package zhangphil.demo;import android.arch.persistence.room.ColumnInfo;import android.arch.persistence.room.Entity;import android.arch.persistence.room.PrimaryKey;/** * Created by Phil on 2017/11/23. */@Entity(tableName = "info_table")public class Info { @PrimaryKey(autoGenerate = true) public int infoId; @ColumnInfo(name = "blog") public String blog; @ColumnInfo(name = "content") public String content;}
(三)需要注意的是,通過Android Room的@Embedded符號內嵌的資料表,列表名將自動二次添加到“宿主”對象中。本例是User鐘內嵌了Info,那麼User資料庫表user_table中將會被Android Room自動添加Info裡面的列名欄位。User的user_table中原有userId,name,age,updateTime四列,由於@Embedded了Info,那麼Info裡面的blog,content將會自動添加到User資料表中。但是Info的主鍵infoId將在User中被忽略不再被作為主鍵。
(四)寫一個MainActivity.java測試:
package zhangphil.demo;import android.arch.persistence.room.Room;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import java.util.List;public class MainActivity extends AppCompatActivity { private String TAG = "輸出"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); new Thread(new Runnable() { @Override public void run() { databaseOperation(); } }).start(); } private void databaseOperation() { UserDatabase mUserDatabase = Room.databaseBuilder(getApplicationContext(), UserDatabase.class, "users").build(); UserDao mUserDao = mUserDatabase.getUserDao(); //寫資料庫 writeUserDatabase(mUserDao, "zhangphil", 18); readDatabase(mUserDao); //關閉資料庫 mUserDatabase.close(); } private void readDatabase(UserDao dao) { Log.d(TAG, "讀資料庫..."); List<User> users = dao.getAllUsers(); for (User u : users) { Log.d(TAG, u.userId + "," + u.name + "," + u.age + ","+u.info.blog+","+u.info.content); } Log.d(TAG, "讀資料庫完畢."); } private void writeUserDatabase(UserDao dao, String name, int age) { Info info = new Info(); info.blog = "http://blog.csdn.net/zhangphil"; info.content = "Android"; User user = new User(); user.name = name; user.age = age; user.updateTime = System.currentTimeMillis(); user.info = info; dao.insertUser(user); }}
代碼運行結果,logcat輸出:
11-24 09:20:00.716 30805-30851/zhangphil.demo D/輸出: 讀資料庫...11-24 09:20:00.723 30805-30851/zhangphil.demo D/輸出: 1,zhangphil,18,http://blog.csdn.net/zhangphil,Android11-24 09:20:00.723 30805-30851/zhangphil.demo D/輸出: 讀資料庫完畢.
附錄:
1,《Android官方ORM資料庫Room技術解決方案簡介(一)》連結:http://blog.csdn.net/zhangphil/article/details/78611632
2,《Android ORMLite資料庫簡介》連結:http://blog.csdn.net/zhangphil/article/details/46878075
3,《Android ORMLite ForeignCollection關聯外部集合》連結:http://blog.csdn.net/zhangphil/article/details/46891021
Android官方ORM資料庫Room技術解決方案:@Embedded內嵌對象(二)