Android官方ORM数据库Room技术解决方案:@Embedded内嵌对象(二)

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 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.



附录:
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 

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