How can I pass sub-report value to main-report? - jasper-reports

Question

Here's the relation table
StudentName
Course
Marks
Peter
Bio
65
Peter
Chem
70
Peter
Music
80
David
Chem
50
How can I make something like the followings
Peter Total : 215
Subject : Bio - 65
Subject : Chem - 70
Subject : Music - 80
Peter Total : 50
Subject : Chem - 50

Answer 1

I would not use a subreport for this as this can be achieved in a simpler way: You can utilize Report groups and variables to achieve this. Make sure that the data is sorted accordingly to the output.
Preparation
Create a report group based on StudentName. Right Click in iReport in the report inspector on the report and select Add Report group. Follow the wizard, give it a name (e.g. Student), select field StudentName as group expression, add header but no footer.
Create a variable that holds the total for a student. Right Click in iReport in the report inspector on Variables and select Add Variable. In the properties panel configure as follows: Name: totalMarkByStudent, Variable Class: java.lang.Long, Calculation: Sum, Reset Type: Group, Reset Group: Student, Variable Expression: $F{Marks}. Leave the rest to its default values.
Report Design
Drag and drop the Field StudentName from the report inspector into the report designer into the Student group header band. There will be a popup asking what kind of value shall be displayed, select The field value and click Ok.
Drag and drop the Variable totalMarksByStudent from the report inspector into the report designer into the Student group header band. Click on the text field and modify following settings in the properties panel:
Width: 200 (to allow more space)
Text field expression: "Total : " + $V{totalMarkByStudent}
Expression Class: java.lang.String
Evaluation Time: Group (meaning that the value gets evaluated once the processing of the group is finished)
Evaluation Group: Student
Drag and drop the fields Course and Marks from the report inspector into the detail band in the report designer. Right click on the course field and select Edit Expression. CHange the expression to "Subject : " + $F{Course} and click on Apply.
With this configuration you achieve a report output as in the image below.
For further reference here the complete JRXML using report group and variable:
<?xml version="1.0" encoding="UTF-8"?>
<jasperReport xmlns="http://jasperreports.sourceforge.net/jasperreports" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports http://jasperreports.sourceforge.net/xsd/jasperreport.xsd" name="report3" language="groovy" pageWidth="595" pageHeight="842" columnWidth="555" leftMargin="20" rightMargin="20" topMargin="20" bottomMargin="20" uuid="0dfbb9b2-a9ce-4447-beee-37d653140dd1">
<property name="ireport.zoom" value="1.0"/>
<property name="ireport.x" value="0"/>
<property name="ireport.y" value="0"/>
<queryString>
<![CDATA[select * from (
Select 'Peter' as StudentName, 'Bio' as Course, 65 as Marks
union select 'Peter', 'Chem', 70
union select 'Peter', 'Music', 80
union select 'David', 'Chem', 50
) tbl
order by StudentName, Course]]>
</queryString>
<field name="StudentName" class="java.lang.String"/>
<field name="Course" class="java.lang.String"/>
<field name="Marks" class="java.lang.Long"/>
<variable name="totalMarkByStudent" class="java.lang.Long" resetType="Group" resetGroup="Student" calculation="Sum">
<variableExpression><![CDATA[$F{Marks}]]></variableExpression>
</variable>
<group name="Student">
<groupExpression><![CDATA[$F{StudentName}]]></groupExpression>
<groupHeader>
<band height="50">
<textField>
<reportElement uuid="ea996b6c-d41d-47bb-bef1-5df580b5c161" x="0" y="30" width="100" height="20"/>
<textElement/>
<textFieldExpression><![CDATA[$F{StudentName}]]></textFieldExpression>
</textField>
<textField evaluationTime="Group" evaluationGroup="Student">
<reportElement uuid="8ddc9b5b-9c57-4fce-8ed0-587c6b54143c" x="180" y="30" width="200" height="20"/>
<textElement/>
<textFieldExpression><![CDATA["Total : " + $V{totalMarkByStudent}]]></textFieldExpression>
</textField>
</band>
</groupHeader>
</group>
<detail>
<band height="20">
<textField>
<reportElement uuid="f67b4e51-4da6-4758-b3d3-bd75de70c0f7" x="0" y="0" width="180" height="20"/>
<textElement/>
<textFieldExpression><![CDATA["Subject : " + $F{Course}]]></textFieldExpression>
</textField>
<textField>
<reportElement uuid="ea82c278-d2f3-4467-bf5d-8dab9ff99ae3" x="180" y="0" width="277" height="20"/>
<textElement/>
<textFieldExpression><![CDATA[$F{Marks}]]></textFieldExpression>
</textField>
</band>
</detail>
</jasperReport>
If you use a subreport instead
I assume that the subreport is paraemterized with the student id shows the data for a given student. The main report shows the field StudentName and the subreport in the detail panel.
Create a variable total in the subreport that calculates the total for the student.
Create a variable totalByStudent in the main report with calculation type set to System.
Click on the subreport and in the properties panel click on Return values. Click Add and select: Subreport variable: total, Local Destination Variable: totalByStudent, rest leave to default. Click on Ok.
Drag and drop the variable totalByStudent into the detail band. Select it and in the Properties panel set Evaluation time to Band. The output will be the same as shown above.
I recommend to use the approach with report group and variable as it reduces the complexity of the report, as well as performance for this way would be better.