In traditional banded-style report writers, reports that can be printed from a
single source of data are quite easy to create. But if the content of the report
onsists of information from several different sources of data, the choices become quite limited. One option is to use SQL to join the data together into one
, and then build the report based on this table. If many tables are involved, the performance of this approach can be prohibitive.
Delphi provides an alternative to this approach by allowing linkages to be established between data access objects. Within
we can use free-form subreports to take advantage of the many configurations these data access objects make possible.
A single data source can be connected directly to the report
via the DataPipeline property. When printed, the report will generate one
detail band for each record provided by the data source.
Independent Data Sources
Here we have three sources
of data with no linkages between them. In this report we want to print all of
the customers, then all of the products, and then all of the vendors. The report
needs to fit together like a book, with each data source providing a ‘chapter’.
Here we use the main report to launch a subreports for each of the data sources.
The subreports would be set with a PrintBehavior of section, which means that
each subreport would start a new page, generate a set of pages as necessary to
traverse all of the data of the data source and then return control to the main
report. The main report is not connected to any data source, so we would
manually stop the report generation process by coding an event handler in the
detail band AfterPrint event. This event handler would call the
Report.DataTraversalCompleted procedure, which would stop the report generation
process after all of the subreports have completed printing.
Master Data Source with Single Detail Data Source
In this scenario, the
master data is connected to the detail data via a field or set of fields. It is
assumed that this connection results in multiple detail records being selected
for each individual master record. The master data source is assigned to the
report, and the detail data source is assigned to the detail band of the report.
The report steps through each of the master records and generates one detail
band for each record in the detail data source. If there are no corresponding
detail records for a given master record, the report generates a blank detail
Master Data Source with Nested Detail Data Sources
Here we have the master
data source containing a list of customers. Each customer has multiple orders;
each order has multiple products, and each product has multiple potential
vendors. This configuration is called ‘nested’ because each set of records is
selected based on the linkage established with the previous data source.
The first two data sources
can be handled as in the standard Master/Detail arrangement. The customer data
source is assigned to the report, and the order data source is assigned to the
detail band. The next two data sources can be handled by a subreport. A
subreport has all of the capabilities of a regular report – the only difference
is that it can be placed within the band of another report. In this case, we
place the subreport in the detail band of the main report. It will then print
once for each order record. Within the subreport, we assign the report to the
part data source and the detail band to the vendor data source.
By configuring the report in this manner, the following information will be
printed: all customers, all orders for each customer, all parts for each order,
and all vendors for each part.
Master Data Source with Multiple Independent Data Sources
Here we have the order
table. Each order has many order items. For each order there is also a group of
vendors that can supply the products for that order. Both of these data sources
are linked to the master data source, as opposed to being nested within one
another; therefore, the data sources are ‘independent’. This type of data can be
handled by placing two subreports in the detail band. The first subreport can be
linked to the order item data source, and the second subreport can be linked to
the vendor data source. In order to print the vendor data after the order item
data, we would link the vendor subreport to the order item subreport via the