Question

I am working with multiple databases within the same application. I am using drivers from two different companies. Both companies have tTable and tQuery Descendants that work well.

I need a way to have generic access to the data, regardless of which driver/tQuery component I am using to return a set of data. This data would NOT tie to components, just to my logic.

For example…(pseudocode) Let’s create a function which can run against either tQuery component

function ListAllTables(NameOfDatabase : String) :ReturnSet??
begin

If NameOfDataBase = 'X' then use tQuery(Vendor 1)
    else use tQuery(Vendor 2)
RunQuery;
Return Answer...
end;

When NORMALLY running a query, I do

Query.Open;
While not Query.EOF do
   begin
   Read my rows..
   next;
end;

If I am CALLING ListAllTables, what is my return type so that I can iterate through the rows? Each tQuery Vendor is different, so I can’t use that (can I, and if so, would I want to?) I could build a Memory Table, and pass that back, but that seems like extra work for ListAllRows to build a memory table, and then to pass it back to the calling routine so that it can “un-build”, i.e. iterate through the rows…

What are your ideas and suggestions?
Thanks
GS

Answer 1

Almost all Delphi datasets descend from TDataset, and most useful behavior is defined on TDataset.

Therefore, if you assign each table or query to a variable of type TDataset, you should be able to perform your logic on that dataset in a vendor neutral fashion.

I would also isolate the production of the datasets into a set of factory functions that only create the vendor-specific dataset and return it as a TDataset. Each factory function goes in it’s own unit. Then, only those small units need have any knowledge of the vendor specific components.