释放一个新版本的应用程序，该应用程序将在数据库Android中更新特定表

Question

我在Google Play市场上发布了一个应用程序。在其中我使用sqlasseThelper库进行数据库连接。实际上，我的应用程序是一个教程应用程序。其中还有一个表存储用户标记的喜欢的问题。现在我想更新问题表，但是我的问题是，如果我发布带有更新的问题表的新版本，那么最喜欢的问题的表将删除？正确的？那么，如何发布我的应用程序的新版本，该版本不会删除用户喜欢的表数据，而只会在该数据库中更新特定的表？我的问题有任何解决方案吗？

thanx提前。

Answer 1

您需要注意您的用户数据，并且SQliteOpenHelper类中有一个onUpgrade()，您可以在其中匹配database version，如果您的数据库版本是更多，则来自以前的版本。在onUpgrade() Fucntion中创建新表格，如果要在现有表中添加新数据，则您需要编写代码以添加新行或通过inert或update查询进行更新。另外，您可以通过alter查询在现有表中添加新列。

请找到有关版本Upgarde的更多信息。

https://riggaroo.co.za/android-sqlite-database-use-onupgrade-correctly/

，如果您在资产中添加了数据库文件以获取初始数据，那么您需要更改数据库pragma版本，而只是数据库版本，我们可以在SQliteOpenHelper类中传递。

参见下面的onupgrade样本（）

在我们的求职中，我们定义了以下内容：

 @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.e(TAG, "Updating table from " + oldVersion + " to " + newVersion);
        //Added new column to book table - book rating 
        if (oldVersion < 2){
            db.execSQL(DROP + BookEntry.TABLE_NAME);
            db.execSQL(BookEntry.SQL_CREATE_BOOK_ENTRY_TABLE);
        }
        //Rename table to book_information - this is where things will start failing.
        if (oldVersion < 3){
            db.execSQL(DROP + BookEntry.TABLE_NAME);
            db.execSQL(BookEntry.SQL_CREATE_BOOK_ENTRY_TABLE);
        }
        // Add new column for a calculated value. By this time, if I am upgrading from version 2 to 
        // version 4, my table would already contain the new column I am trying to add below, 
        // which would result in a SQLException. These situations are sometimes difficult to spot, 
        // as you basically need to test from every different version of database to upgrade from. 
        // Some upgrades might work and some might fail with this method.
        // It is best to follow the other method that is on the master branch of this repo.
        if (oldVersion < 4){
            db.execSQL("ALTER TABLE " + BookEntry.TABLE_NAME  + " ADD COLUMN calculated_pages_times_rating INTEGER;");
        }
        //As you can probably imagine, this is a terrible way to do upgrades, Please DONT DO IT!!!!
     }

       @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            Log.e(TAG, "Updating table from " + oldVersion + " to " + newVersion);
            //Added new column to book table - book rating 
            if (oldVersion < 2){
                db.execSQL(DROP + BookEntry.TABLE_NAME);
                db.execSQL(BookEntry.SQL_CREATE_BOOK_ENTRY_TABLE);
            }
            //Rename table to book_information - this is where things will start failing.
            if (oldVersion < 3){
                db.execSQL(DROP + BookEntry.TABLE_NAME);
                db.execSQL(BookEntry.SQL_CREATE_BOOK_ENTRY_TABLE);
            }
            // Add new column for a calculated value. By this time, if I am upgrading from version 2 to 
            // version 4, my table would already contain the new column I am trying to add below, 
            // which would result in a SQLException. These situations are sometimes difficult to spot, 
            // as you basically need to test from every different version of database to upgrade from. 
            // Some upgrades might work and some might fail with this method.
            // It is best to follow the other method that is on the master branch of this repo.
            if (oldVersion < 4){
                db.execSQL("ALTER TABLE " + BookEntry.TABLE_NAME  + " ADD COLUMN calculated_pages_times_rating INTEGER;");
            }
            //As you can probably imagine, this is a terrible way to do upgrades, Please DONT DO IT!!!!

        }

Answer 2

当您在sqliteopenhelper类中更改数据库版本时 void onupgrade（sqlitedatabase db， int Oldversion， int newversion）将为拥有旧数据库版本的用户称呼。您应该在此处修改数据库，以在新的数据库版本中包括您的修改。如果您从此方法中删除Drop Table命令，则将不会删除现有用户数据