java - Is the onUpgrade method ever called?

Question

Is the onUpgrade method of SQLiteOpenHelper ever called? If so, when is it called and by what? If it is not called by the developers, then why is it there? What really happens with that function? I have seen examples where it drops all the tables, but then a comment says that dropping all the tables is not what you should do. Any suggestions?

Answer 1

For those of you who would like to know the exact moment when onUpgrade() gets called, it is during a call to either getReadableDatabase() or getWriteableDatabase().

To those who are not clear how it ensure it gets triggered, the answer is: It is triggered when the database version provided to the constructor of SqLiteOpenHelper is updated. Here is a example

public class dbSchemaHelper extends SQLiteOpenHelper {

private String sql;
private final String D_TAG = "FundExpense";
//update this to get onUpgrade() method of sqliteopenhelper class called
static final int DB_VERSION = 2; 
static final String DB_NAME = "fundExpenseManager";

public dbSchemaHelper(Context context) {
    super(context, DB_NAME, null, DB_VERSION);
    // TODO Auto-generated constructor stub
}

now to...onUpgrade()

@Override
public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
    sql = "ALTER TABLE " + fundExpenseSchema.Expense.TABLE_NAME + " ADD COLUMN " + fundExpenseSchema.Expense.FUNDID + " INTEGER";
    arg0.execSQL(sql);
}