Android官方ORM数据库Room技术解决方案:@Embedded内嵌对象(二)
(一)附录1简介了Android Room的基本使用。在附录1例子中,User对象元素均为普通的Java基本数据类型,但是实际的开发中,通常建立的持久化存储对象复杂,且通常是结构化的Java对象,互相之间存在引用或者内嵌关系。
Android Room支持数据库表Java对象通过注解符@Embedded内嵌一个Java对象。这样就像过去的ORM数据库一样,比如构造一个名为Info的Java对象,作为一个成员变量添加到User里面:
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对象本身也是一个Android Room的@Entity。也有自己的列名和主键等完整的Android Room数据表要素,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,通过Android Room的@Embedded符号内嵌的数据表,列表名将自动二次添加到“宿主”对象中。本例是User钟内嵌了Info,那么User数据库表user_table中将会被Android Room自动添加Info里面的列名字段。User的user_table中原有userId,name,age,updateTime四列,由于@Embedded了Info,那么Info里面的blog,content将会自动添加到User数据表中。但是Info的主键infoId将在User中被忽略不再被作为主键。
(四)写一个MainActivity.java测试:
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 = "输出";
@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();
//写数据库
writeUserDatabase(mUserDao, "zhangphil", 18);
readDatabase(mUserDao);
//关闭数据库
mUserDatabase.close();
}
private void readDatabase(UserDao dao) {
Log.d(TAG, "读数据库...");
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, "读数据库完毕.");
}
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);
}
}
代码运行结果,logcat输出:
11-24 09:20:00.716 30805-30851/zhangphil.demo D/输出: 读数据库...
11-24 09:20:00.723 30805-30851/zhangphil.demo D/输出: 1,zhangphil,18,http://blog.csdn.net/zhangphil,Android
11-24 09:20:00.723 30805-30851/zhangphil.demo D/输出: 读数据库完毕.
1,《Android官方ORM数据库Room技术解决方案简介(一)》链接:http://blog.csdn.net/zhangphil/article/details/78611632
2,《Android ORMLite数据库简介》链接:http://blog.csdn.net/zhangphil/article/details/46878075
3,《Android ORMLite ForeignCollection关联外部集合》链接:http://blog.csdn.net/zhangphil/article/details/46891021