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POHibernate: shuffling child nodes in a bidirectional ordered tree
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2012-10-14T20:48:02.227
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2012-10-14T22:14:44.987
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I have a basic tree structure composed of a simple <code>Node</code> class, linking bidirectionally to it's single parent (can be null for root nodes) and an ordered list of children: <pre><code>public class Node { private Integer xid; private Node parent; private List<Node> children; // getters and setters... } </code></pre> I map this using hibernate to the following simple database table: <pre><code> > select * from node; xid | parent | xorder -----+--------+-------- 1 | NULL | 0 2 | 1 | 0 3 | 1 | 1 4 | 1 | 2 (4 rows) </code></pre> Using the following <code>.hbm</code> hibernate mapping file: <pre><code><class name="Node" table="node"> <id name="xid" type="int"> <generator class="native" /> </id> <many-to-one name="parent" /> <list name="children" table="node"> <key column="parent" /> <list-index column="xorder" /> <one-to-many class="Node" /> </list> </class> </code></pre> However, when I try to shuffle elements order within one parent using the following code: <pre><code>@Transactional public void testNode() { Node parent = (Node) getSession().get(Node.class, 1); Node child0 = parent.getChildren().remove(0); parent.getChildren().add(1, child0); // Swap first and second child getSession().update(parent); } </code></pre> I get an exception when hibernate flush the transaction: (<code>org.hibernate.exception.ConstraintViolationException ... set parent=null, xorder=null where parent='1' and xid='2'</code>): basically the update try to set <code>xorder</code> to <code>null</code>, which is obviously forbidden by the database schema. I tried many combination on the hbm mapping, with no success. When I set the <code><list></code> to <code>inverse="true"</code> hibernate does not do any update, setting <code>insert="false" update="false"</code> on the <code><many-to-one></code> element does not help neither. I probably miss something here, either in the <code>hbm</code> mapping or in my code, my feeling is that it should be pretty obvious... Any idea?
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<java><hibernate><orm><tree><hbm>
Title
Hibernate: shuffling child nodes in a bidirectional ordered tree
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1. USLaurent Grégoire
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