Android SqLite升级

android开发中，如果大家使用到了sqlite就会牵涉到它的升级问题，因为升级后的表结构可能完全不一样，会有字段的添加或者删除等。。
   sqlite升级思路：
     1：将表A重新命名：例如重新命名为：temp_A
     2：创建新标A
    3： 将temp_A中的数据【也就是更新前的数据】插入到新表A
   我的案例分两种：1：一张表字段发生变化  2： 数据库中添加新的表
   先看1：一张表字段发生变化  
   直接代码走起：
   SQLiteOpenHelper类：
    
package com.example.sqldbupdatedemo;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
/****
 * 
 * @author jone
 *
 *  2013-12-2
 *  com.example.sqldbupdatedemo
 *
 */
public class MySqlHelper extends SQLiteOpenHelper
{
//DB name
public static final String DB_NAME = "TestUp.db";

//初始的版本号
public static final int DB_VERSION = 1;

//表名称
public static String tname = "myup";

//创建表的sql语句
public static final String CREATE_TASK_TB = "create table if not exists " + tname + "(name text,pwd text)";

public MySqlHelper(Context context, String name, int version)
{
super( context, name, null, version );
// TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db)
{
// TODO Auto-generated method stub
db.execSQL( CREATE_TASK_TB );
Log.i( "tag", "oncreat db" );

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
Log.i( "tag", " onUpgrade db" );
//获取到旧表中的字段【也就是新表中保留的字段】
String columns = getColumnNames( db, tname );
//升级
updateTable( db, tname, columns );
}

private void updateTable(SQLiteDatabase db, String tableName, String columns)
{

try
{

db.beginTransaction();
String reColumn = columns.substring( 0, columns.length() - 1 );
// rename the table
String tempTable = tableName + "texp_temptable";
String sql = "alter table " + tableName + " rename to " + tempTable;
db.execSQL( sql );

// drop the oldtable
String dropString = "drop table if exists " + tableName;
db.execSQL( dropString );
// creat table
String ss = "create table if not exists " + tableName + "(name text,pwd text,rpwd text)";
db.execSQL( ss );
// load data
String newStr = "rpwd";
String newreColumn = reColumn + "," + newStr;
String ins = "insert into " + tableName + " (" + newreColumn + ") " + "select " + reColumn + "" + " " + " from "
+ tempTable;
db.equals( ins );
db.setTransactionSuccessful();
}
catch (Exception e)
{
// TODO: handle exception
Log.i( "tag", e.getMessage() );
}
finally
{
db.endTransaction();
}

}

// 获取升级前表中的字段
protected String getColumnNames(SQLiteDatabase db, String tableName)
{
StringBuffer sb = null;
Cursor c = null;
try
{
c = db.rawQuery( "PRAGMA table_info(" + tableName + ")", null );
if (null != c)
{
int columnIndex = c.getColumnIndex( "name" );
if (-1 == columnIndex)
{
return null;
}

int index = 0;
sb = new StringBuffer( c.getCount() );
for ( c.moveToFirst(); !c.isAfterLast(); c.moveToNext() )
{
sb.append( c.getString( columnIndex ) );
sb.append( "," );
index++;
}
}
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
if (c != null)
{
c.close();
}
}

return sb.toString();
}

}
具体的使用者Activity
  
package com.example.sqldbupdatedemo;

import java.util.ArrayList;

import android.app.Activity;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener
{

MySqlHelper dbHelper;

SQLiteDatabase db;

TextView tView1;

TextView tView2;

TextView tView3;

Button button;

Entity entity1；

Entity entity2;

ArrayList<Entity> list;

@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate( savedInstanceState );
setContentView( R.layout.activity_main );
dbHelper = new MySqlHelper( this, MySqlHelper.DB_NAME, 7 );
list = new ArrayList<MainActivity.Entity>();
initView();
initSql();
}

private void showInfo()
{
db = dbHelper.getReadableDatabase();
Cursor cursor = null;
try
{

cursor = db.rawQuery( "select * from myup", null );
while (cursor.moveToNext())
{
String name = cursor.getString( cursor.getColumnIndex( "name" ) );
String pwd = cursor.getString( cursor.getColumnIndex( "pwd" ) );
String rpwd = cursor.getString( cursor.getColumnIndex( "rpwd" ) );
// String myl = cursor.getString( cursor.getColumnIndex( "myl" ) );
Entity entity = new Entity( name, pwd, rpwd );
list.add( entity );
}
}
catch (Exception e)
{
// TODO: handle exception
e.printStackTrace();
Log.i( "tag", e.getMessage() );
}

if (cursor != null)
{
cursor.close();
db.close();
}
entity1 = list.get( 0 );
entity2 = list.get( 1 );
tView1.setText( entity1.getName() + "---" + entity1.getPwd() + "--" + entity1.getRpwd() );
tView2.setText( entity2.getName() + "---" + entity2.getPwd() + "--" + entity2.getRpwd() );
}

private void initView()
{
tView1 = (TextView) findViewById( R.id.en1 );
tView2 = (TextView) findViewById( R.id.en2 );
tView3 = (TextView) findViewById( R.id.en3 );
button = (Button) findViewById( R.id.btn );
button.setOnClickListener( this );
}

private void initSql()
{

db = dbHelper.getWritableDatabase();
String insert1 = "insert into myup(name,pwd) values(?,?)";
db.execSQL( insert1, new String[] { "zhangsan", "123456" } );
String insert2 = "insert into myup(name,pwd) values(?,?)";
db.execSQL( insert2, new String[] { "lisi", "789654" } );
db.close();
}

class Entity
{

String name;

String pwd;

String rpwd;

public Entity(String name, String pwd, String rwpd)
{
this.name = name;
this.pwd = pwd;
this.rpwd = rpwd;
}

public String getName()
{
return name;
}

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

public String getPwd()
{
return pwd;
}

public void setPwd(String pwd)
{
this.pwd = pwd;
}

public String getRpwd()
{
return rpwd;
}

public void setRpwd(String rpwd)
{
this.rpwd = rpwd;
}

}

@Override
public void onClick(View v)
{
switch (v.getId())
{
case R.id.btn:
showInfo();
break;

default:
break;
}

}

}
注释比较详细了
接下来是第二中情况：2 数据库中添加新的表
数据库升级的逻辑定义。。这点其实是数据库升级最重要的部分，我们在升级之前要定义好相应的升级逻辑，当我们在创建SQLiteOpenHelper类会传入不同的版本号，此刻我们更具这个version来做升级逻辑。。
例如我们的app已经有了两个版本V1.0,V1.2,现在我们在开发V1.3,那么我们对应的数据库版本号依次为18,19,20
对于这种情况，我们应该如何实现升级？
用户的选择有：                   
1） V1.0 -> V1.3  DB 18 -> 20                  
2） V1.1 -> V1.3  DB 19 -> 20    
注意： 数据库每一个版本所代表的数据库必须是定义好的，比如说：V18数据库有两张表T1,T2,如果V19要添加一张表T3,V20要修改T3中的某些字段则逻辑是这样子的：
  V18--> T1,T2
  V19-->T1,T2,T3
 V20-->T1,T2,T3(更新)
在onUpgrade()方法的实现如下：
 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
int upgradeVersion  = oldVersion;

if (18 == upgradeVersion) {
// Create table T3
String sql = "CREATE TABLE ...";
db.execSQL(sql);
upgradeVersion = 1
}

if (20 == upgradeVersion) {
// Modify table T3
upgradeVersion = 20;
}

if (upgradeVersion != newVersion) {
// Drop tables
db.execSQL("DROP TABLE IF EXISTS " + tableName);
// Create tables
onCreate(db);
}
}