Maybe I found a bug in the report module of Mendix. I setted up a Report Pane with an Basic Report and a Report Chart in a table. I connected the Basic Report and the Report Chart with my Data Set. I also have two parameters in my Data Set. I started first with the Basic Report to see, if my OQL statement works well. Everthing is ok here. I have two dropdowns in my report pane where I can select the parameters and the output is correct. But the Report Chart ignores the parameters in the dropdown totally! The chart is displaying all the data always. I also removed the Basic Report above to see if this influences the chart... We need these reports for displaying results from a answered questionnaire. I also tried to setup SimpleChart or FusionChart, but they do not work with DataSets or is there another solution. I don't want to create persistent-counting-dummies.... This should not be the solution!
Could you post the OQL constraints just to confirm that you don't have a syntax error that is causing that problem.
If your syntax is correct, it would unfortunately mean that you have found a bug in the reporting functionality of the platform.
DataSets can only be used and accessed through the build in reporting functionality. Those are not usable by any widget, currently not even from Java.
I wish I could give you a better answer but I am afraid that at this point your only option would be to use the SimpleChart or FusionChart widget with persistent entities.