Android数据库升级解决方案
一、SQLiteOpenHelper介绍
SQLiteOpenHelper有两个方法， public void onCreate(SQLiteDatabase db)以及public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)。第一次安装App时onCreate(SQLiteDatabase db)会被系统回调，通常在onCreate(SQLiteDatabase db)中创建数据表；当数据库版本升级时，系统会回调onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)，通常在onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)中做数据库升级方案。数据库的版本号在SQLiteOpenHelper的构造方法中传入。
二、数据库升级方案
1、onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)详细介绍
在创建SQLiteOpenHelper时传入的数据库版本号如果大于当前版本App数据库文件的版本号onUpgrade会被系统回调。oldVersion为当前版本App数据库文件的版本号， newVersion为SQLiteOpenHelper传入的数据库版本号，newVersion肯定大于oldVersion。
2、举例说明
假设App已经发版过V1、V2，即将发版V3。V1创建了数据表feedback，数据库版本为1；V2在V1的feedback基础上增加了一个字段username，数据库版本为2；V3在V2的基础上新增了一个表crash，数据库版本为3。V1发版时SQLiteOpenHelper如下：
public class DBOpenHelper extends SQLiteOpenHelper {
private static final String TAG = DBOpenHelper.class.getSimpleName();
public DBOpenHelper(Context context) {
super(context, "feedback.db", null, 1);
}
@Override
public void onCreate(SQLiteDatabase db) {
LogUtil.log(TAG, "onCreate");
String createSql = "create table feedback (" +
" online integer," +
" speechtype integer," +
" priority integer ," +
" domain char(100)," +
" keyparams char(200)," +
" success integer," +
" errorcode integer," +
" errormsg char(100)," +
" network integer," +
" networktype integer," +
" ip char(32)," +
" userid char(100)," +
" userphone char(20)," +
" useraddress char(200)," +
" starttime bigint," +
" finishtime bigint" + ")";
db.execSQL(createSql);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
LogUtil.log(TAG, "onUpgrade");
}
}V2需要将feedback增加一个字段username，用户从V1升级到V2时，需要改变库表结构并且将原来的feedback进行迁移，V2发版时SQLiteOpenHelper如下：
public class DBOpenHelper extends SQLiteOpenHelper {
private static final String TAG = DBOpenHelper.class.getSimpleName();
public DBOpenHelper(Context context) {
super(context, "feedback.db", null, 2);
}
/**
* 新增字段username
* @param db
*/
@Override
public void onCreate(SQLiteDatabase db) {
LogUtil.log(TAG, "onCreate");
String createSql = "create table feedback (" +
" online integer," +
" speechtype integer," +
" priority integer ," +
" domain char(100)," +
" keyparams char(200)," +
" success integer," +
" errorcode integer," +
" errormsg char(100)," +
" network integer," +
" networktype integer," +
" ip char(32)," +
" userid char(100)," +
" username char(100),"+
" userphone char(20)," +
" useraddress char(200)," +
" starttime bigint," +
" finishtime bigint" + ")";
db.execSQL(createSql);
}
/**
* 用户从V1升级到V2时改变库表结构并将V1数据库中的数据进行迁移
* @param db
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
LogUtil.log(TAG, "onUpgrade");
if (oldVersion==1) {//用户当前是V1版本
//重命名
String rename = "alter TABLE feedback RENAME TO feedback_temp";
db.execSQL(rename);
//建立新表
onCreate(db);
//数据拷贝
String copy = "insert into feedback(online,speechtype,priority,domain,keyparams,success,errorcode,errormsg,network,networktype,ip,userid,userphone,useraddress,starttime,finishtime) " +
"select (online,speechtype,priority,domain,keyparams,success,errorcode,errormsg,network,networktype,ip,userid,userphone,useraddress,starttime,finishtime) from feedback_temp";
db.execSQL(copy);
//删除原表
String delete = "drop table feedback_temp";
db.execSQL(delete);
}
}
}V3在V2的基础上增加了表crash，用户升级方案可能是：V1-V2，V1-V3,V2-V3，V3发版时SQLiteOpenHelper如下：
public class DBOpenHelper extends SQLiteOpenHelper {
private static final String TAG = DBOpenHelper.class.getSimpleName();
public DBOpenHelper(Context context) {
super(context, "feedback.db", null, 3);
}
/**
* 建表feedback、crash
*
* @param db
*/
@Override
public void onCreate(SQLiteDatabase db) {
LogUtil.log(TAG, "onCreate");
String createFeedbackSql = "create table feedback (" +
" online integer," +
" speechtype integer," +
" priority integer ," +
" domain char(100)," +
" keyparams char(200)," +
" success integer," +
" errorcode integer," +
" errormsg char(100)," +
" network integer," +
" networktype integer," +
" ip char(32)," +
" userid char(100)," +
" username char(100)," +
" userphone char(20)," +
" useraddress char(200)," +
" starttime bigint," +
" finishtime bigint" + ")";
String createCrashSql = "create table crash (starttime bigint,finishtime bigint)";
db.execSQL(createFeedbackSql);
db.execSQL(createCrashSql);
}
/**
* 升级方案可能为V1-V2；V1-V3；V2-V3
*
* @param db
* @param oldVersion
* @param newVersion
*/
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
LogUtil.log(TAG, "onUpgrade");
switch (oldVersion) {
case 1://用户当前是V1版本
if (newVersion == 2) {//升级到V2
upgradeToV2(db);
} else if (newVersion == 3) {//升级到V3
upgradeToV2(db);
upgradeToV3(db);
}
break;
case 2://用户当前是V2版本
if (newVersion == 3) {//升级到V3
upgradeToV3(db);
}
break;
}
}
private void upgradeToV2(SQLiteDatabase db) {
//重命名
String rename = "alter TABLE feedback RENAME TO feedback_temp";
db.execSQL(rename);
//建立新表
String createFeedbackSql = "create table feedback (" +
" online integer," +
" speechtype integer," +
" priority integer ," +
" domain char(100)," +
" keyparams char(200)," +
" success integer," +
" errorcode integer," +
" errormsg char(100)," +
" network integer," +
" networktype integer," +
" ip char(32)," +
" userid char(100)," +
" username char(100)," +
" userphone char(20)," +
" useraddress char(200)," +
" starttime bigint," +
" finishtime bigint" + ")";
db.execSQL(createFeedbackSql);
//数据拷贝
String copy = "insert into feedback(online,speechtype,priority,domain,keyparams,success,errorcode,errormsg,network,networktype,ip,userid,userphone,useraddress,starttime,finishtime) " +
"select * from feedback_temp";
db.execSQL(copy);
//删除原表
String delete = "drop table feedback_temp";
db.execSQL(delete);
}
private void upgradeToV3(SQLiteDatabase db) {
String createCrashSql = "create table crash (starttime bigint,finishtime bigint)";
db.execSQL(createCrashSql);
}
}