Crystal Reports: COM Data Sources

COM data sources: gateways to data in your legacy systems.

This is really information for developers, but users can gain insight from it as well.

These COM data sources have been available for a couple of versions now and we are only just discovering how useful they can be. A COM data source is an ADO record set created by a VB program. You then use this as the source of data for your report.

The Visual Basic code is as simple as:

Public Function MyDataSource() As ADODB.Recordset 
Dim rsOut As New ADODB.Recordset 
‘Some code to build the rsOut recordset…. 
Set MyDataSource = rsOut 
End Function

So, where can you use one? Anywhere your data are not stored in a convenient database, but can be retrieved using Visual Basic. We have read of suggestions of using one to retrieve some legacy data from another system, or reading a text file.

If you can write some Visual Basic code to see the data and present them to a user, then you can wrap the function code above around your code, and compile it into a DLL. Register the DLL and use that to send your data to your Crystal Report.

Now, here's something very interesting to end-users, Crystal Report writers, and Crystal Report admins. A COM data driver is the key to our cViewIMAGE utility. cViewIMAGE is a COM data driver that can reference an image file in a field and return the embedded image to use in your report. This is an excellent way to raise the perceived value of any report and increase your own job security!

Click here for an example of how to include a single image in a report.

See below for a Microsoft table that shows data types used in COM. The source for this is http://msdn.microsoft.com/en-us/library/sak564ww.aspx

This article is copyrighted by Crystalkeen, Mindconnection, and Chelsea Technologies Ltd. It may be freely copied and distributed as long as the original copyright is displayed and no modifications are made to this material. Extracts are permitted. The names Crystal Reports and Seagate Info are trademarks owned by Business Objects.