android數據庫的升級的寫法

    public abstract class DbBaseTable {  

        private static final String TAG = "DbBaseTable";  

        /** 
         * @return the DB table name 
         */  
        abstract String getName();  

        /** 
         * Creates the DB table according to the DB scheme 
         *  
         * @param db 
         */  
        abstract void onCreate(SQLiteDatabase db);  

        void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion, String tempName) {  

            //Rename old table to temporary name  
        DbUtils.renameTable(db, getName(), tempName);  

            //Create clear table according to the new scheme  
           onCreate(db); 
            //Copy content of the matching columns from the old table to the new one  
          joinColumns(db, tempName, getName()); 

            //Delete old table  
          DbUtils.dropTable(db, tempName); 

            //這個是更新一些表的內容  
            initTableContent(db);  
        }  

        void initTableContent(SQLiteDatabase db) {  
        }  

        void joinColumns(SQLiteDatabase db, String tempName, String tableName) {  
          DbUtils.joinColumns(db, tempName, tableName);  
        }  

    }  

    final class DbUtils {  

        private static final String TAG = "DbUtils";  
        private static final boolean DEBUG = false;  

        private static final String SQLITE_STMT_LIST_TABLES =  
            "SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%' AND name NOT LIKE 'android%'";  
        private static final String SQLITE_TABLE_NAME_COLUMN = "name";  
        private static final String SQLITE_STMT_TEMPLATE_LIST_COLUMNS = "SELECT * FROM %s LIMIT 1";  
        private static final String SQLITE_STMT_TEMPLATE_DROP_TABLE = "DROP TABLE IF EXISTS %s";  
        private static final String SQLITE_STMT_TEMPLATE_RENAME_TABLE = "ALTER TABLE %s RENAME TO %s";  
        private static final String SQLITE_STMT_TEMPLATE_COPY_COLUMNS = "INSERT INTO %s (%s) SELECT %s FROM %s";  


        /** 
         * @param db 
         * @return Collection object containing table names in the database  
         */  
        static Collection<String> listTables(SQLiteDatabase db) {  

            Cursor cursor = db.rawQuery(SQLITE_STMT_LIST_TABLES, null);  
            if (cursor == null || !cursor.moveToFirst()) {  

                if (cursor != null) {  
                    cursor.close();  
                }  
                return null;  
            }  

            int table_name_column = cursor.getColumnIndex(SQLITE_TABLE_NAME_COLUMN);  
            HashSet<String> tables = new HashSet<String>(cursor.getCount());  
            do {  
                tables.add(cursor.getString(table_name_column));  
            } while (cursor.moveToNext());  
            cursor.close();  


            return tables;  
        }  


        /** 
         * @param db 
         * @param table 
         * @return List of column names in the DB table 
         */  
        public static List<String> listColumns(SQLiteDatabase db, String table) {  

            Cursor cursor = db.rawQuery(String.format(SQLITE_STMT_TEMPLATE_LIST_COLUMNS, table), null);  
            if (cursor == null) {  
                return null;  
            }  

            List<String> columns = Arrays.asList(cursor.getColumnNames());  
            cursor.close();  

            return columns;  
        }  


        /** 
         * @param db 
         * @param table 
         */  
        static void dropTable(SQLiteDatabase db, String table) {  

            db.execSQL(String.format(SQLITE_STMT_TEMPLATE_DROP_TABLE, table));  
        }  


        static void renameTable(SQLiteDatabase db, String oldName, String newName) {  

            db.execSQL(String.format(SQLITE_STMT_TEMPLATE_RENAME_TABLE, oldName, newName));  
        }  


        static void joinColumns(SQLiteDatabase db, String oldTable, String newTable) {  

            //Delete all records in the new table before copying from the old table  
            db.delete(newTable, null, null);  

            //Find columns which exist in both tables  
            ArrayList<String> old_columns = new ArrayList<String>(listColumns(db, oldTable));  
            List<String> new_columns = listColumns(db, newTable);  
            old_columns.retainAll(new_columns);  

            String common_columns = TextUtils.join(",", old_columns);  

            //Copy records from old table to new table  example:         INSERT INTO Mytest1 (_id,account_id,test1,test3) SELECT _id,account_id,test1,test3 FROM Mytest1_temp_ 
            db.execSQL(String.format(SQLITE_STMT_TEMPLATE_COPY_COLUMNS, newTable, common_columns, common_columns, oldTable));  
        }  

    }  

    @Override  
       public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {  

           //Get table names in the old DB  
           Collection<String> old_tables = DbUtils.listTables(db);  
           if (old_tables == null || old_tables.size() == 0) {  
               onCreate(db);  
               return;  
           }  

           //Get table names in the new DB  
           Set<String> new_tables = DataBaseClass.sRCMDbTables.keySet();  

           try {  
               db.beginTransaction();  
               //Remove old tables which are not in the new DB scheme  
               HashSet<String> obsolete_tables = new HashSet<String>();  
               for (String table : old_tables) {  
                   if (!new_tables.contains(table)) {  
                    System.out.println("====DBHelp onUpgrade droptable table="+table);  
                       DbUtils.dropTable(db, table);  
                       obsolete_tables.add(table);  
                   }  
               }  
               old_tables.removeAll(obsolete_tables);  

               //Create and upgrade new tables   
               DbBaseTable table_descriptor;   
               for (String table : new_tables) {  
                   table_descriptor = DataBaseClass.sRCMDbTables.get(table);  

                   //Check if the new table exists in the old DB  
                   if (old_tables.contains(table)) {  
                       String temp_name = getTempTableName(table, old_tables, new_tables);  
                       System.out.println("====DBHelp onUpgrade temp_name ="+temp_name);  
                       table_descriptor.onUpgrade(db, oldVersion, newVersion, temp_name);  
                   } else {  
                       table_descriptor.onCreate(db);  
                   }  
               }  
               db.setTransactionSuccessful();  
           } catch (Throwable e) {  

               throw new RuntimeException("DB upgrade failed: " + e.getMessage());  
           } finally {  
               db.endTransaction();  
           }  
       }