How to implement one to many relation in ofbiz

How can I implement one to many relationship in ofbiz between two entities, I have a entity Plan which can have many number of Items(other entity), I have defined relation in entityModel.xml :

     <entity entity-name="Plan"
        package-name="org.ofbiz.webapp.terp.plan" title="plan entity">
        <field name="planId" type="id-ne"> <description>Primary sequence ID</description> </field>
        <field name="divisionId" type="id-ne"></field>
        <field name="transactionTypeId" type="id-ne"></field>
        <field name="planCode" type="very-short"></field>
        <field name="planName" type="short-varchar"></field>
                <relation rel-entity-name="Item" type="many" fk-name="item_id">
        <key-map field-name="itemId"/>
        </relation>               
      </entity>

In the add form of plan given by entity engine item is a simple text box, so how can I add multiple items for a plan?

Is there a UI widget in ofbiz which allows us to select multiple items for one plan while we are adding new plan.

If there is no widget, any online tutorial on implementing something like this.