android 数据库的版本,android-具有4个数据库版本的SQLite onUpgrade

当我们有4个数据库版本并且在每个版本的用户表中添加了一个新字段时,如何正确执行SQLiteOpenHelper的onUpgrade方法？

变体A：//在每种情况下都没有“中断”,它是否在情况2和3中继续运行？

public void onUpgrade(SQLiteDatabase database, int version_old, int current_version) {

switch (version_old) {

case 1:

database.execSQL(addPostcodeFieldToUserTable);

case 2:

database.execSQL(addGenderFieldToUserTable);

case 3:

database.execSQL(addEmailSubscriptionFieldToUserTable);

break;

}

}

变体B：

public void onUpgrade(SQLiteDatabase database, int version_old, int current_version) {

switch (version_old) {

case 1:

database.execSQL(addPostcodeFieldToUserTable);

break;

case 2:

database.execSQL(addPostcodeFieldToUserTable);

database.execSQL(addGenderFieldToUserTable);

break;

case 3:

database.execSQL(addPostcodeFieldToUserTable);

database.execSQL(addGenderFieldToUserTable);

database.execSQL(addEmailSubscriptionFieldToUserTable);

break;

}

但是,如果用户拥有数据库的版本1,然后错过了版本2,并使用版本3升级了应用程序,我们该怎么办？

变体3：

public void onUpgrade(SQLiteDatabase database, int version_old, int current_version) {

if(version_old==1 && current_version==2) {

database.execSQL(addPostcodeFieldToUserTable);

} else if(version_old==2 && current_version==3) {

database.execSQL(addGenderFieldToUserTable);

} else if(version_old==3 && current_version==4) {

database.execSQL(addEmailSubscriptionFieldToUserTable);

} else if(version_old==1 && current_version==3) {

database.execSQL(addPostcodeFieldToUserTable);

database.execSQL(addGenderFieldToUserTable);

} else if(version_old==1 && current_version==4) {

database.execSQL(addPostcodeFieldToUserTable);

database.execSQL(addGenderFieldToUserTable);

database.execSQL(addEmailSubscriptionFieldToUserTable);

} else if(version_old==2 && current_version==4) {

database.execSQL(addGenderFieldToUserTable);

database.execSQL(addEmailSubscriptionFieldToUserTable);

}

}