Recursive Mapping of collections

[Echo.Narcissus Echo]

http://docs.jboss.org/hibernate/core/3.3/reference/en/html/collections.html... really has me befuddled.

I am trying to create a ToDo List with Vaadin/ Hibernate /Spring /MySQL.

So my <hibernate mapping> looks like this

<hibernate-mapping>
    <class name="com.intellizens.ribbon.tasks.model.Task" table="task" >
        <id name="taskId" type="java.lang.Long">
            <column name="taskId" />
            <generator class="identity" />
        </id>
        <set name="children" >
            <key column="parentId" not-null="true" update="false" />
            <one-to-many class="com.intellizens.ribbon.tasks.model.Task"/>
        </set>
        <property name="parentId" type="java.lang.Long">
            <column name="parentId" length="45" not-null="true" />
        </property>
..
</hibernate-mapping>

And my Task.java thus

public class Task implements Serializable {

	private Collection<Task> children = new ArrayList<Task>();
..
}

I am expecting that each Task in the Task table will have an entry ParentId which in relation to TaskId (indexed key of the table) will give the one-to-many parent to child collection mapping.

Obviously it seems that this mapping is not something i understood very well.
Because hibernate complains ..

nested exception is org.hibernate.MappingException: Repeated column in mapping for entity: com.intellizens.ribbon.tasks.model.Task column: parentId (should be mapped with insert="false" update="false")

Or is it that i am expecting hibernate to read my mind.. and making a obvious mistake.

[Waswani Naresh]

Hi Echo,

You are probably trying to do some thing like....

One task can have multiple sub-tasks and each task will have its parent task ID.

Try this approach


Task.java

public class Task {

	private Long taskID;
	private Set<Task> subtasks;
	
	public Long getTaskID() {
		return taskID;
	}

	public void setTaskID(Long taskID) {
		this.taskID = taskID;
	}

	public Set<Task> getSubtasks() {
		return subtasks;
	}

	public void setSubtasks(Set<Task> subtasks) {
		this.subtasks = subtasks;
	}

Task.hbm.xml
<hibernate-mapping package="junk"> <class name="Task" table="Task" > <id name="taskID"> <generator class="assigned"></generator> </id> <set name="subtasks" table="Task" cascade="all"> <key column="PARENT_ID"></key> <one-to-many class="Task" /> </set> </class> </hibernate-mapping>

Do let me know if this serves the purpose.

Regards,
Naresh Waswani

[Echo.Narcissus Echo]

Thanks for your response.

What about the parentId mapping?

<property name="parentId" type="java.lang.Long">
<column name="parentId" length="45" not-null="true" />
</property>

[Waswani Naresh]

Look at the key element with in the set. Its mapped to PARENT_ID. So you don't need to define it separately.

Regards,
Naresh Waswani