调用sqlite onUpgrade问题

Question

I have 2 databases. 1 is a MySQL where I use a games API to gather the up-to-date information about a game. The other database I have is a sqlite DB that I created in my app (both have the same tables and columns). How I want this to work is, the app starts then the MySQL version will be checked (updated whenever the game I play has an update) I check to see if the MySQL version matches the sqlite version and update when needed.

The confusion I am having is I do not want the users to have to update the entire app when a minor MySQL DB change happens (An item stat gets changed, an item gets added, a character gets added or the stat of an ability of a character gets tweaked) because what I am seeing on here and in Vogella tutorials is that it seems I need to actually change manually:

private static final int DATABASE_VERSION = 1;  //<<<<<Manually change this
...

public MySQLiteHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

which defeats the purpose I am trying to accomplish.

1) Is there a way to update the DATABASE_VERSION without actually having to manually change it in the code?

2) Can I just straight out call onUpgrade(db, oldVersion, newVersion) and put the parameters I want or is this a very bad idea and it should be handled through getWritableDatabase() ?

Answer 1

The database version is changed only, when the table structure has changed, ie tables are added or deleted or when some columns change, being added or removed. When this is the case and a new version of your app is installed, then Android detects the new database version and calls onUpgrade .

If you just update the data in your tables, there is no change in the table structure and therefore no need to increase the database version number.

In your case, you can add some serial number or timestamp in one of your columns, which identifies the current data version and compare that against the version or timestamp stored in the corresponding SQLite database table.

When these differ, you can update the data from the MySQL database.

Update :

When you update your app, but the table structure is unchanged, then the database version should stay the same and the database and its data remains untouched.

When you update your app and the table structure changes, you increase the database version number. Android compares the current and the new version and calls onUpgrade . Now you can do the necessary steps to upgrade your database, change the database layout, populate new tables or columns, whatever needs to be done. You can even destroy everything and build a new database from scratch.

All this is independent from the day to day update, when your app runs and pulls current data from the main server database.

Answer 2

It sounds like you are reading your schema from a central MySQL database and simply keeping a local copy on the Android device. When you change the central database's schema, yes, it's silly to manually change the local copy.

1) Is there a way to update the DATABASE_VERSION without actually having to manually change it in the code?

DATABASE_VERSION is just like any other variable, if you want to control it's value from an outside source, you can. Honestly you don't even need this variable, it is only used in SQLiteOpenHelper's constructors :

SQLiteOpenHelper(Context context, String name, 
        SQLiteDatabase.CursorFactory factory, int version)

SQLiteDatabase maintains it's own private version number.

2) Can I just straight out call onUpgrade(db, oldVersion, newVersion) ...?

I don't recommend doing this because you will not be changing the internal version number and skipping other internal checks used by SQLiteOpenHelper.
Yes, you can perform many of these checks manually, but for every work-around that you create you are making SQLiteOpenHelper less useful. At some point you are better off calling Context#openOrCreateDatabase() directly since you will have created your own version control code.