Dynamic SQL

Purpose

This demo shows how to retrieve schema and/or data via SQL generated at runtime.

When you compile and run the server, you will see it contains a memo displaying "SQL details generated for Update will be displayed here". The demo does not actually attempt to update server data but merely display the fields that would be updated by processing the delta. See the TDynSQLService.UpdateData code in DynSQLService_Impl to see how the delta is being processed.

Having next compiled and run the client, the first thing to try is clicking on the Retrieve Schema and Data button and you should then see the Customers data displayed in the grid. Changing the text in the memo, e.g. to Select * from "Order Details" and clicking the button again results in the display of a different dataset with a totally different schema. Any of the datasets in the database (Northwind, by default) may be accessed in this manner.

Other points of interest:

• As their names suggest, the Retrieve Schema and Retrieve Data buttons achieve the same as the Retrieve Schema and Data button. You might want to use them separately if the data has the same layout as the schema already retrieved. For example, having retrieved all the records (Max Records = -1), you can change the number of records required and select Retrieve Data because the schema is correct. If you change the actual SQL though, you will need to reload the schema.
• Save and Load buttons. Save stores the schema and data in Data.dat in the sample folder. If you only want to save the schema, set Max Records = 0 and retrieve schema and data (otherwise Save cannot work because the dataset is not open). Load restores the schema and any records saved no matter what data is currently open. Thus you can think of retrieve and load as similar operations but with remote and local data respectively.
• The Update button simulates updating the dataset. You can see the result in the memo contained in the server form.