Update and Maintain dbExpress's Unidirectional, Read-Only Datasets By Bob Swart, Delphi Pro
The good old Borland Database Engine (or any other Delphi data access library before dbExpress) provided datasets that had a bi-directional cursor, and they were directly connected to the database table. Even with a TQuery, you could use the RequestLive property to try and update the resulting dataset. Now with dbExpress, this is no longer the case. The datasets (TSQLDataSet, TSQLTable, TSQLQuery, or TSQLStoredProc) are not only unidirectional (they support moving one step ahead or all the way back to the beginning, but no other operations), they also are read-only. So we have no direct way to post a new or changed record to a TSQLDataSet.
After I've made changes to the datasets in a dbExpress application, when I exit and restart the application the datasets revert to their old values. How do I post a new or changed record to a dbExpress dataset when dbExpress provides only unidirectional, read-only datasets?
Using the ClientDataSet, which can utilize the DataSetProvider, you can connect back to the original dbExpress database. Then, using the ApplyUpdates method, you can drop a TButton on the Form and set its Caption property to Apply Updates. Another solution is to make it an automatic (apply) update. Apart from using a TSQLDataSet that uses a TDataSetProvider to put the records in a TClientDataSet component, we could also have used a TSQLClientDataSet component that in effect contains the three aforementioned components in one. And once you've selected the solution, make the solution code uniform and reusable.
Do you expect dbExpress to replace the Borland Database Engine, especially since Kylix supports only dbExpress? Let us know in the Database Development discussion groups!
