Multiple queries in a single jasper document

It is possible to use execute multiple queries from a single report by using a subDataset and datasetRun. The behaviour is like having one or more subreports embedded into a single report file.

Define a subDataset like this:

<subDataset name="dataset1">
    <parameter name="someParam" class="java.lang.String"/>
    <queryString><![CDATA[SELECT column1, column2 FROM table1 WHERE column1=$P!{someParam}]]></queryString>
    <field name="column1" class="java.lang.String"/>
    <field name="column2" class="java.lang.String"/>
</subDataset>

Subdatasets can have parameters, fields, variables and groups just like a report can. Each subdataset can have it's own query, and the report can have as many subdatasets as you want.

To use a subdataset, you need to define a datasetRun. This can only be done inside particular elements: charts, crosstabs, tables and lists. We will use a list as it behaves almost exactly like another detail band.

This code defines a list that uses our subdataset:

<componentElement>
    <reportElement x="0" y="0" width="100" height="40"/>
    <jr:list xmlns:jr="http://jasperreports.sourceforge.net/jasperreports/components" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports/components http://jasperreports.sourceforge.net/xsd/components.xsd">
        <datasetRun subDataset="dataset1">
            <datasetParameter name="someParam"><datasetParameterExpression><![CDATA["some value for column 1"]]></datasetParameterExpression></datasetParameter>
        </datasetRun>
        <jr:listContents height="40">
            <textField>
                <reportElement x="0" y="0" width="100" height="20"/>
                <textElement/>
                <textFieldExpression class="java.lang.String"><![CDATA[$F{column1}]]></textFieldExpression>
            </textField>
            <textField>
                <reportElement x="0" y="20" width="100" height="20"/>
                <textElement/>
                <textFieldExpression class="java.lang.String"><![CDATA[$F{column2}]]></textFieldExpression>
            </textField>
        </jr:listContents>
    </jr:list>
</componentElement>

Some notes:

• The jr:listContents element is analogous to a detail band element. You can place almost any other elements inside.

• The datasetRun element is much like a subreport element. It can have a dataSourceExpression or connectionExpression inside, which will change where the data comes from. If neither of these are present, the report datasource is used.

• The same subDataset can be used by many datasetRuns, so you can easily run a query multiple times with different parameters.