Change Property Type by Code?

General
1

Hi,

i use a global property in my app to handle my SQLite-Methods. The Property is called DB and has a type SQLiteDatabase. Now i want to change my OpenDatabase-Method to check first, if there is a MySQL-Connection. If not, load the local SQLite Database.

The best way for me would be to change the Property Type (DB) from SQLiteDatabase to MySQLCommunityServer. But i didn’t get how to change the properties type by code. Is there any chance to do this?

Michael

2

There is no easy way to do this. You can do an interface for the databases and then do wrapper classes for the functionality.

The problem is that the databases are fundamentally different and you need to do some OO to get the databases to behave in a similar manner.

3

Thanks Beatrix,

i expected it would not be that easy. Have to over-think my concept.

Thanks again,

Michael

4

Easy: declare the property as Database, the super class of SQLiteDatabase and MySQLCommunityServer.

5

Two key concepts to get you going in the right direction. Casting and ISA.

dim db as Database
db = new sqlitedatabase   // valid
db.DatabaseFile = f     // not valid
db = new mysqlcommunityserver   // valid
db.host = "10.0.0.1"   // not valid

Solve those problems by testing the type of object db holds with ISA and then casting to the appropriate type to access the specific properties.

dim db as Database
db = new ???
if db ISA sqlitedatabase then
   sqlitedatabase(db).DatabaseFile = f
elseif db ISA mysqlcommunityserver then
   mysqlcommunityserver(db).host = "10.0.0.1"
end
6

Ok,

first of all thanks for your help and ideas. I managed it a different way. To post code would be a bit much to read, but in simple words i realized to switch between Offline- (SQLite) and Online-Mode (MySql) by using 2 different global properties (SQLiteDB and MySqlDB) and build in some litte if-statements in my db-methods.

Example:

User starts app, we try to connect a MySqlDB, if connect went fine, a property OfflineMode is set to False. This property is checked in all of my database-methods. If connect went wrong, the property OfflineMode is set to True and the database-methods use a local copy (SQLite) of my database instead. We are also implementing a sync-process, so the user can still create datasets when offline.

Hope i can release this app (it will be a CRM, mostly needed by ourselves) in the App Store within the next months.

regards

Michael