Using same Dataset for multiple tables or list in a report problem

[OnettoHector]

Hello. Im new to BIRT
I have cretead a scripted dataSource and a scripted dataSet for it.
I have the following code:
In the "Initialize" script of the report:

importPackage(Packages.com.datasul.technology.webdesk.dataset);
importPackage(Packages.java.util);

var dataset = null;
var count = 0;

In the "beforeOpen" script of the dataset:

try{
var factory = DatasetFactory.getInstance(${WKCompany}); 

dataset = factory.getDataset("DSAltaProducto", null, null, null)
}
catch(e){
}
finally{
}

In the "fetch" script of the dataset:

if (dataset != null) {
if (count < dataset.rowsCount){
	row["codigoProducto"] = dataset.getValue(count, "codigo");
	row["nombreProducto"] = dataset.getValue(count, "nombre");
	count++
	return true; 
}
}
return false;

This code seems to work fine. When I drag the dataSource into my design layout it creates a table that displays all of the results just fine.
The problem is, when I try to add another table with the same dataset, nothing is displayed in this second table, its just blank.
Same thing when I create a Data component and bind it to a dataset field, the first one will display fine, and the second one will be blank.
I think im missing an important part about how the dataset operates, so I would appreciate any help.
Thanks in advance

[hvbtup]

You have to set count=0 in the beforeOpen event (without var).
I recommend to use report variables for things like this, just to make it more visible to the next developer that the code needs global variables.

[OnettoHector]

Thanks a lot! that fixed it.
May I ask, why is it necessary to reassign the value in the beforeOpen event when I've already assigned it a value in the "Initialize" event?
Im sorry if it's a basic question but I cant seem to find in-depth documentation, do you have a website to point to? I know there's eclipse-birt.github.io/birt-website/docs but the info seems pretty basic
Thanks again!

[hvbtup]

Scripted datasets are an advanced topic IMHO.

Your report is a special case, beause you said that you want to reuse a dataset more than once in the same report.

For those readers who wonder "Why?": There are typical use-cases for this scenario (see below).
If your report doesn't fit into these scenarios, please tell us what your use-case is - maybe there is a less complicated solution, then.

Each time you use the data set, you want to iterate over the records.
Thus your record counter has to be reset in the open event.
When using a dataset, the sequence of events is open, fetch (for each record), close.

If you don't reset your count variable, it is still after the end of the records, so at the second time, you'll see no rows.

Use-cases:

a) You want to show the same data twice in a different form.
E.g. You start your report with a grouped table with "hide details" checked at some group level, so that the reader can see a summary immediately.
Then, you show the same data again, but now with all the details.
b) You want to re-use the dataset in the same report, but with different data (of course the dataset needs data set parameters then).
c) In very rare cases, I use this to combine a list item and a table item based on the same data; I use "hide details" in a group on the list item, then add the table to the group footer, and filter the data so that the outcome is more or less as if I had it all in one table, the difference being that at the outer level I don't have a table, which is useful for MS Word output to avoid nested tables.