example for using a datasource as a subdataset in jasper report without using a subreport

[simonseyock]

I struggled some time to use the datasource created by !datasource and !createDatasource as a subdataset in jasper. I wanted to share my findings as the documentation is very unclear in that regard (it is not explained how the datasource is treated inside jasper and what is provided to the report and how to read that). So here it is:

config.yaml

templates:
  name: !template
    attributes:
      data: !datasource
        attributes:
          key1: !string {}
          key2: !string {}
    processors:
      - !reportBuilder
        directory: '.'
      - !createDataSource
        processors: []
        inputMapper:
          data: datasource
        outputMapper:
          jrDataSource: someDatasource

report.jrxml (excerpts)

<subDataset name="someDataset">
  <queryString>
    <![CDATA[]]>
  </queryString>
  <field name="key1" class="java.lang.String"/>
  <field name="key2" class="java.lang.String"/>
</subDataset>
<!-- ... -->
<parameter name="someDatasource" class="net.sf.jasperreports.engine.JRDataSource"/>
<!-- ... -->
<datasetRun subDataset="someDataset">
  <dataSourceExpression>$P{someDatasource}</dataSourceExpression>
</datasetRun>

Cheers 🍻