In Real life Student can assign to multiple course. Here we see example of One to Many where student can assign to many courses. Create service in portlet. Add below content in your portlet service. <entity name="Student" local-service="true" remote-service="true" cache-enabled="false"> <column name="studentId" type="long" primary="true" /> <column name="courses" type="Collection" entity="Course"/> </entity> <entity name="Course" local-service="true" remote-service="true" cache-enabled="false"> <column name="courseId" type="long" primary="true" /> <column name="studentId" type="long"/> <finder name="courseId" return-type="Collection"> <finder-column name="courseId" /> </finder> ...