Android下使用SQLite数据库

情况4: 数据库文件存在, 版本号降低, 执行onDowngrade()方法, 方法中默认会抛出一个异常

代码：MySQLiteOpenHelper.java

package com.oterman.mysqlite;

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

public class MySQLiteOpenHelper extends SQLiteOpenHelper {
	/**
	 * 由于父类没有默认的无参数的构造函数，故需要显示的写出构造函数，然后去调用父类有参数的构造函数；
	 * 参数1：context表示应用程序的环境，用来确定数据库文件的位置；
	 * 参数2：数据库文件的名字；
	 * 参数3：用来创建结果集Cursor的工厂，默认传入null；
	 * 参数4：数据的版本号，从1开始；
	 * @param context
	 * @param version
	 */

	public MySQLiteOpenHelper(Context context,int version) {
		super(context,"myfirstdb.db",null,version);
	}
	

	public MySQLiteOpenHelper(Context context) {
		super(context,"myfirstdb.db",null,1);
	}
	
	
	/**
	 * 如果数据库文件不存在，调用该方法；
	 */
	@Override
	public void onCreate(SQLiteDatabase db) {
		System.out.println("数据库创建啦");
		db.execSQL("create table account(_id Integer primary key autoincrement,name varchar(40))");
		
	}

	/**
	 * 数据库文件存在，版本号发生变化，会调用该方法；
	 */
	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
		System.out.println("数据库升级啦");

	}

}

事务结束的时候, 会把最后一个成功标记之前的操作提交, 成功标记之后的操作回滚

代码：Accout.java

package domain;

public class Account {

	private Integer id ;
	private String name;
	private Integer balance ;
	public Account(Integer id, String name, Integer balance) {
		super();
		this.id = id;
		this.name = name;
		this.balance = balance;
	}
	public Account() {
		super();
	}
	public Integer getId() {
		return id;
	}
	public Account(String name, Integer balance) {
		super();
		this.name = name;
		this.balance = balance;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getBalance() {
		return balance;
	}
	public void setBalance(Integer balance) {
		this.balance = balance;
	}
	@Override
	public String toString() {
		return "Account [id=" + id + ", name=" + name + ", balance=" + balance + "]";
	}
	
	
	
	
	
}

package com.oterman.dao;

import java.util.ArrayList;
import java.util.List;

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

import com.oterman.mysqlite.MySQLiteOpenHelper;

import domain.Account;

public class AccountDao {
	private Context context;
	
	
	public AccountDao(Context context) {
		this.context = context;
	}

	public void insert(Account a){
		//获取数据库；
		MySQLiteOpenHelper helper=new MySQLiteOpenHelper(context);
		SQLiteDatabase db=helper.getWritableDatabase();
		//操作数据库；
		db.execSQL("insert into account values(null,?,?)",new Object[]{a.getName(),a.getBalance()});
		//关闭数据库；
		db.close();
	}
	//删除记录；
	public void delete(int i) {
		MySQLiteOpenHelper helper=new MySQLiteOpenHelper(context);
		SQLiteDatabase db=helper.getWritableDatabase();//获取数据库；
		db.execSQL("delete from account where _id=?",new Object[]{i});
		db.close();
	}
	
	//修改数据库；
	public void update(){
		MySQLiteOpenHelper helper=new MySQLiteOpenHelper(context);
		SQLiteDatabase db=helper.getWritableDatabase();
		db.execSQL("update account set balance=? where _id<?",new Object[]{1000,9});
		db.close();
	}
	//查询数据库；
	public Account query(int i) {
		//获取数据库；
		MySQLiteOpenHelper helper=new MySQLiteOpenHelper(context);
		SQLiteDatabase db=helper.getWritableDatabase();
		//执行查询语句；获取结果集；
		Cursor c=db.rawQuery("select name,balance from account where _id=?", new String[]{i+""});
		Account a=null;
		while(c.moveToNext()){
			String name=c.getString(0);
			int balance=c.getInt(1);
			a=new Account(i,name,balance);
		}
		return a;
	}
	
	//查询所有；
	public List<Account> queryAll(){
		MySQLiteOpenHelper helper=new MySQLiteOpenHelper(context);
		SQLiteDatabase db=helper.getWritableDatabase();
		List<Account> list=new ArrayList<Account>();
		
		String sql="select * from account";
		Cursor c=db.rawQuery(sql, null);
		
		while(c.moveToNext()){
			int id=c.getInt(0);
			String name=c.getString(c.getColumnIndex("name"));
			int balance=c.getInt(c.getColumnIndex("balance"));
			list.add(new Account(id,name,balance));
		}
		c.close();
		db.close();
		return list;
		
	}
	//演示事务
	public void trans(int fromId,int toId, int amount) {
		
		MySQLiteOpenHelper helper=new MySQLiteOpenHelper(context);
		SQLiteDatabase db=helper.getWritableDatabase();
		
		String sql1="update account set balance=balance-? where _id=?";
		String sql2="update account set balance=balance+? where _id=?";
		try{
			db.beginTransaction();//开启事务；
			
			db.execSQL(sql1, new Object[]{amount,fromId});
			db.execSQL(sql2, new Object[]{amount,toId});
			db.setTransactionSuccessful();//可以设置多个标记点；分组提交；如果在标记点之前未出现异常，则之前的所有的sql操作提交；
			
			db.execSQL(sql1, new Object[]{amount,fromId});
			db.execSQL(sql2, new Object[]{amount,toId});
			db.setTransactionSuccessful();
			
			db.execSQL(sql1, new Object[]{amount,fromId});
			int i=1/0;
			db.execSQL(sql2, new Object[]{amount,toId});
			db.setTransactionSuccessful();//标记点；出现异常时，该标记点至上一个标记点的所有内容被回滚；
			
		}finally{
			db.endTransaction();
			db.close();
		}
	}
	

}