Thursday, 13 November 2014

GemStone based reports & views

My current project is a port of a VisualWorks & GemStone fat client application to Seaside. Part of the porting effort was to map a few thousand VW windowSpec views to a Seaside web views. It all works fine, but it's not ideal. Ported fixed layout views look like fat client windows; they lack a web aesthetic. We want all new views to be more 'web-centric', where positioning and sizing is adjusted by the browser, especially from tablets and mobile devices.

We also need to provide reports. For a web app, answering a PDF for a report works well.

We combined these two requirements and ended up with reports generated on GS using a Seaside-like coding pattern, which is then rendered in by Seaside in VW, and can be viewed as a PDF.

To build the reports we use Report4PDF, something I wrote a few years ago.  It uses PDF4Smalltalk to generate a PDF document. PDF4Smalltalk has not been ported to GemStone, something I'd like to do when time allows (and to VA & Pharo). Fortunately, Report4PDF generates intermediate output before requiring PDF4Smalltalk. This output can be created on GS, which is then moved to VW, where PDF4Smalltalk is used for the final output.

Our VW to GS interface uses only strings, either XML or evaluated command strings. In this case, the report objects are packaged as XML, and then recreated on VW. For most reports building and parsing the content takes about 200ms (we may move this to a command string, which is typically a third faster).

Once the report is in VW we use a 'report component' for the rendering, which reads the report content and builds the Seaside output. Because Report4PDF has a Seaside-like coding style, the mapping is relatively simple.

For example, a table is defined as...

aTable row: [:row | 
row cell: [:cell | cell widthPercent: 20. cell text bold; string: 'Job'].
row cell: [:cell | cell widthPercent: 30. cell text; string: self job description].
row cell: [:cell | cell widthPercent: 20. cell text bold; string: 'Our Job ID'].
row cell: [:cell | cell widthPercent: 30. cell text; string: self job id]].

...and gets rendered as...

...the PDF output is... build the PDF content we use the data already in VW.  No additional GS call is needed.

R4PObject, the root Report4PDF class, has a #properties instance variable to support extensions. We use this to add link and update capabilities to the report when it is rendered in Seaside.

For example, a link to another domain object is coded as...
row cell right bold string: 'Designer'.
row cell text normal string linkOop: self designer domainOop; string: self designer displayKeyString.

...and displayed as...

...but is ignored in the PDF output...

The beauty of this approach is that all of the report generation is done on GemStone, with generic rendering and PDF generation in our VW Seaside code.

Our users are happy with this approach. They like the look of the web rendered report and the option to get the content as a PDF. Having link and simple update capabilities means that most users will not need to use the old fat clients views, which tend to be used by power users, for data entry and for detailed updates.

Simple things should be simple. Complex things should be possible. - Alan Key

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