学步园

银行转账

1)update person set amount=amount-10 where personid=1;

2)update person set amount=amount+10 where personid=2;

以上个例子为基础，修改DBOpenHelper类，增加amount字段升级数据库

package cn.leigo.service;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBOpenHelper extends SQLiteOpenHelper {

	public DBOpenHelper(Context context) {
		super(context, "leigo.db", null, 3);  //<包>/databases/
	}

	@Override
	public void onCreate(SQLiteDatabase db) {// 数据库第一次被创建的时候调用的
		db.execSQL("CREATE TABLE person (personid integer primary key autoincrement, name varchar(20))");
	}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		db.execSQL("ALTER TABLE person ADD amount integer");
	}

}

在Person类中增加amount变量:

package cn.leigo.domain;

public class Person {
	private Integer id;
	private String name;
	private String phone;
	private Integer amount;

	public Person() {
	}

	public Person(String name, String phone, Integer amount) {
		this.name = name;
		this.phone = phone;
		this.amount = amount;
	}

	public Person(Integer id, String name, String phone, Integer amount) {
		this.id = id;
		this.name = name;
		this.phone = phone;
		this.amount = amount;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getPhone() {
		return phone;
	}

	public void setPhone(String phone) {
		this.phone = phone;
	}

	public Integer getAmount() {
		return amount;
	}

	public void setAmount(Integer amount) {
		this.amount = amount;
	}

	@Override
	public String toString() {
		return "Person [id=" + id + ", name=" + name + ", phone=" + phone
				+ ", amount=" + amount + "]";
	}

}

修改报错的类

更新数据

	public void testUpdateAmount() throws Exception {
		PersonService service = new PersonService(getContext());
		Person person1 = service.find(1);
		Person person2 = service.find(2);
		person1.setAmount(100);
		person2.setAmount(50);
		service.update(person1);
		service.update(person2);
	}

	public void payment() {
		SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
		// 开启事务
		db.beginTransaction();
		db.execSQL("UPDATE person SET amount=amount-10 where personid=1");
		//System.out.println(1/0);
		db.execSQL("UPDATE person SET amount=amount+10 where personid=2");
		db.setTransactionSuccessful();
		// 结束事务，有两种情况:commit、rollback
		// 事务的提交或者回滚是由事务的标识决定的，如果事务的标识为true,事务就会提交否则回滚，默认情况下事务的标识为false
		db.endTransaction();
		db.close();

	}

	public void testPayment() throws Exception {
		PersonService service = new PersonService(getContext());
		service.payment();
	}

将

System.out.println(1/0);

前的注释去掉，重新测试，测试失败，数据未修改。