How to get multiple field as comma separated values in grid column?

[michalg]

Hi,
I need some help in the following scenario:
I would like to get the grid column filled with comma separated list of validFrom dates for each person like on this picture:


Person.xml data looks like:

<response>
    <data>
        <Person>
            <id>351</id>
            <code>michalg</code>
            <certificate>
                <Certificate>
                    <id>535</id>
                    <certificateType>
                        <id>521</id>
                        <code>pisanie na klawiaturze</code>
                    </certificateType>
                    <validFrom>2017-05-19</validFrom>
                    <issuedBy>komisja nadzoru biurowcow</issuedBy>
                    <documentNo>abcd321</documentNo>
                </Certificate>
                <Certificate>
                    <id>34383</id>
                    <certificateType>
                        <id>521</id>
                        <code>pisanie na klawiaturze</code>
                    </certificateType>
                    <validFrom>2017-05-20</validFrom>
                    <issuedBy>komisja nadzoru programistow</issuedBy>
                    <documentNo>qwerty123_pl</documentNo>
                </Certificate>
                <Certificate>
                    <id>533</id>
                    <certificateType>
                        <id>521</id>
                        <code>pisanie na klawiaturze</code>
                    </certificateType>
                    <validFrom>2017-05-21</validFrom>
                    <issuedBy>komisja nadzoru programistow</issuedBy>
                    <documentNo>qwerty123</documentNo>
                </Certificate>
                <Certificate>
                    <id>34382</id>
                    <certificateType>
                        <id>521</id>
                        <code>pisanie na klawiaturze</code>
                    </certificateType>
                    <issuedBy>komisja nadzoru programistow</issuedBy>
                    <documentNo>qwerty123_en</documentNo>
                </Certificate>
            </certificate>
        </Person>
    </data>
    <requestedDataSource>Person</requestedDataSource>
    <status>STATUS_SUCCESS</status>
</response>

I am using the following test code:

package pl.com.tech4.client;

import com.google.gwt.core.client.EntryPoint;
import com.smartgwt.client.data.DataSource;
import com.smartgwt.client.data.DataSourceField;
import com.smartgwt.client.data.OperationBinding;
import com.smartgwt.client.data.fields.DataSourceTextField;
import com.smartgwt.client.types.AutoFitWidthApproach;
import com.smartgwt.client.types.DSDataFormat;
import com.smartgwt.client.types.DSOperationType;
import com.smartgwt.client.types.DSProtocol;
import com.smartgwt.client.widgets.grid.ListGrid;

public class MainEntryPoint implements EntryPoint {
  
    @Override
    public void onModuleLoad() {

        layout();
    }
  
    private void layout() {

        DataSource personDS = new DataSource();
        personDS.setID("Person");
        OperationBinding fetchBinding = new OperationBinding();
        fetchBinding.setOperationType(DSOperationType.FETCH);
        fetchBinding.setDataFormat(DSDataFormat.XML);
        fetchBinding.setDataProtocol(DSProtocol.POSTXML);
        personDS.setOperationBindings(fetchBinding);
        personDS.setDataURL("Person.xml");
      
        DataSourceField idField = new DataSourceField();
        idField.setName("id");
        idField.setPrimaryKey(true);
        idField.setHidden(true);
       
        DataSourceTextField codeField = new DataSourceTextField();
        codeField.setName("code");

        DataSourceField certificate_validFromField = new DataSourceField();
        certificate_validFromField.setName("certificate_validFrom");
        certificate_validFromField.setValueXPath("certificate/Certificate/validFrom");
        certificate_validFromField.setMultiple(true);
        //can not get comma separated list of dates without the following line:
        //certificate_validFromField.setTypeAsDataSource(new DataSource());

        personDS.setFields(idField, codeField, certificate_validFromField);
       
        ListGrid lg = new ListGrid();
        lg.setDataSource(personDS);
        lg.setAutoFetchData(true);
        lg.setAutoFitFieldWidths(true);
        lg.setAutoFitWidthApproach(AutoFitWidthApproach.BOTH);
        lg.setWidth(300);
        lg.draw();
    }
  
}

Although I am using multiple=true attribute of certificate_validFromField and the proper xpath="certificate/Certificate/validFrom", I got only one first date displayed:

But if I uncomment the line:

        certificate_validFromField.setTypeAsDataSource(new DataSource());

then I got dates as comma separated list as desired.
For sure this is not the right way to go, as it brakes other things - I am not able to get comma separated list of dates any other way.
What am I missing here?
Thanks,
MichalG