How to update p:dataTable in p:rowExpansion

In my project, I have intertwined 2 datatables. I want to update second datatable when first datatable's rows expanded.

<h:form id="form2">
     <p:dataTable var="modules" value="#{EVMView.allModules}" id="mydatatable"> 
        <f:facet name="header">
            Modules
        </f:facet>
        <p:column style="width:2rem">
            <p:rowToggler/>
        </p:column>
        <p:column headerText="Module">
            <h:outputText value="#{modules}"/>
        </p:column>
        
         <p:rowExpansion>
            <div class="product">
                 <p:dataTable var="questions" value="#{EVMView.allQuestions}" id="mydatatable2"> 
                    <p:column style="width:2rem">
                        <p:rowToggler/>
                    </p:column>
                    <p:column headerText="Question">
                        <h:outputText value="#{questions}"/>
                    </p:column>
                    
                    <p:rowExpansion>
                    
                    </p:rowExpansion>
                 </p:dataTable>
            </div>
         </p:rowExpansion>
     </p:dataTable>
</h:form>

When I expand mydatatable's row, I don't see the values in mydatatable2.

So I know I have to update mydatatable2 too, but I couldn't find how to do it.

EDİT

According to @Jasper's answer, I added ViewScoped in my bean and I added this ajax in my first datatable.

<p:ajax event="rowToggle" listener="#{EVMView.updateTable2()}"/>

My bean is like this

package com.utc.pw.ui;

import java.util.List;

import javax.annotation.PostConstruct;
import javax.ejb.EJB;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;

import org.primefaces.PrimeFaces;

import com.utc.pw.domain.EVMOptions;
import com.utc.pw.domain.EVMQuestions;
import com.utc.pw.domain.SalesOrder;
import com.utc.pw.service.EVMService;
import com.utc.pw.service.PublicService;

@ManagedBean(name="EVMView")
@ViewScoped
public class EVMView {
    @EJB
    private PublicService publicService;
    @EJB
    private EVMService evmService;
    
    private EVMQuestions evmQuestions=new EVMQuestions();
    
    private String strSO;
    private List<SalesOrder> salesOrders;
    private List<String> allModules;
    private List<EVMQuestions> allQuestions;
    private String selectedOption;
    private List<EVMOptions> optionList;
    private String answer;
    
    public String getAnswer() {
        return answer;
    }
    public void setAnswer(String answer) {
        this.answer = answer;
    }
    public List<EVMOptions> getOptionList() {
        return optionList;
    }
    public void setOptionList(List<EVMOptions> optionList) {
        this.optionList = optionList;
    }
    public String getSelectedOption() {
        return selectedOption;
    }
    public void setSelectedOption(String selectedOption) {
        this.selectedOption = selectedOption;
    }
    public List<EVMQuestions> getAllQuestions() {
        return allQuestions;
    }
    public void setAllQuestions(List<EVMQuestions> allQuestions) {
        this.allQuestions = allQuestions;
    }
    public PublicService getPublicService() {
        return publicService;
    }
    public void setPublicService(PublicService publicService) {
        this.publicService = publicService;
    }
    public EVMService getEvmService() {
        return evmService;
    }
    public void setEvmService(EVMService evmService) {
        this.evmService = evmService;
    }
    public EVMQuestions getEvmQuestions() {
        return evmQuestions;
    }
    public void setEvmQuestions(EVMQuestions evmQuestions) {
        this.evmQuestions = evmQuestions;
    }
    public String getStrSO() {
        return strSO;
    }
    public void setStrSO(String strSO) {
        this.strSO = strSO;
    }
    public List<SalesOrder> getSalesOrders() {
        return salesOrders;
    }
    public void setSalesOrders(List<SalesOrder> salesOrders) {
        this.salesOrders = salesOrders;
    }
    public List<String> getAllModules() {
        return allModules;
    }
    public void setAllModules(List<String> allModules) {
        this.allModules = allModules;
    }
    @PostConstruct
    public void init()  {
        this.salesOrders = publicService.getAllSalesOrders();
        
    }
    public void loadModules()
    {
        this.allModules=evmService.getAllModules(strSO);
        this.allQuestions=evmService.getAllQuestions(strSO);
        PrimeFaces.current().ajax().update("form2:mydatatable");
        //PrimeFaces.current().ajax().update("form3:mydatatable2");
    }
    public void updateTable2()
    {
        PrimeFaces.current().ajax().update(":mydatatable2");
    }
    public List<EVMOptions> options(String module,int questionID)
    {
        this.optionList=evmService.getOptions(strSO, module, questionID);
        
        return optionList;
    }
}

Solution

You don't need to update the table in the p:rowExpansion when it is expanded as it is lazy loaded by default. What you do need to do is make sure that you child p:dataTable value="#{...}" is set correctly. To do so, add a listener on the outer p:dataTable and set the model based on the expanded row. You will need to use the rowToggle event, which takes a ToggleEvent as the parameter.

As your table has multiple rows of modules, you should have model in your bean which can contain multiple modules, like a Map with the module ID as the key and the questions as the value. Add module entries in your rowToggle handler.

Also make sure your bean is at least ViewScoped.