Hi all
I met a strange question. I have two tables poheader and poitem. Relationship is one-to-many. I have maintained bidirectional relationship and do save them to my mysql database.
Insert is OK. But when I open the database, I found the insert sequence is reverse. For example, there are two items 10 and 20, I want hibernate do insert 10 first then to insert 20. But the actual situation is reverse, hibernate insert 20 firstly. I am sure I add items orderly.
Could anyone tell me what had happend?

Hibernate version:2.1.3
Database MySQL version: 4.0.18
Operate System: WindowXP SP1
Develop Environment: Eclipse 3.0

Mapping documents:
<hibernate-mapping package="com.npb.hibernate">
<class name="Poheader" table="poheader">
<id name="id" column="ID" type="java.lang.Long" unsaved-value="0">
<generator class="native"/>
</id>
<property name="poNumber" column="PO_NUMBER" unique="true" type="java.lang.String" />
<property name="docDate" column="DOC_DATE" type="java.lang.String" />
<property name="docType" column="DOC_TYPE" type="java.lang.String" />
<property name="purchOrg" column="PURCH_ORG" type="java.lang.String" />
<property name="purGroup" column="PUR_GROUP" type="java.lang.String" />
<property name="vendor" column="VENDOR" type="java.lang.String" />
<set name="poitems" lazy="true" inverse="true" cascade="all" >
<key column="PO_NUMBER"/>
<one-to-many class="Poitem" />
</set>
</class>

<hibernate-mapping package="com.npb.hibernate">

<class name="Poitem" table="poitem">
<id name="id" column="ID" type="java.lang.Long" unsaved-value="0">
<generator class="native" />
</id>
<property name="poItem" column="PO_ITEM" type="java.lang.String" />
<property name="material" column="MATERIAL" type="java.lang.String" />
<property name="plant" column="PLANT" type="java.lang.String" />
<property name="storeLoc" column="STORE_LOC" type="java.lang.String" />
<property name="netPrice" column="NET_PRICE" type="java.lang.Long" />
<property name="delivDate" column="DELIV_DATE" type="java.lang.String" />
<property name="quantity" column="QUANTITY" type="java.lang.Long" />
<many-to-one name="poheader" property-ref="poNumber" column="PO_NUMBER" class="Poheader" not-null="true"/>
</class>
</hibernate-mapping>


I am working on legacy system, so I use "property-ref" that is not encouraged in Hibernate Reference.

This is code fragment about maintain parent and child:
............
public void setPoitems(Set poitems){
this.poitems = poitems;
}

public Set getPoitems(){
return poitems;
}

public void add(Poitem poitem){
poitem.setPoheader(this);
poitems.add(poitem);
}
...................


My test program:
public class test {

public static void main(String[] args) {
Poheader header = new Poheader();
header.setDocDate("20041120");
header.setDocType("NB");
header.setPoNumber("ponumber");
header.setPurchOrg("1000");
header.setPurGroup("001");
header.setVendor("1000");
Poitem item1 = new Poitem();
item1.setDelivDate("20041120");
item1.setPoItem("10");
item1.setMaterial("test1");
item1.setNetPrice(new Long(9));
item1.setPlant("1000");
item1.setQuantity(new Long(10));
item1.setStoreLoc("0001");
header.add(item1);

Poitem item2 = new Poitem();
item2.setDelivDate("20041120");
item2.setPoItem("20");
item2.setMaterial("test2");
item2.setNetPrice(new Long(39));
item2.setPlant("1000");
item2.setQuantity(new Long(20));
item2.setStoreLoc("0002");
header.add(item2);

Session session = HibernateUtil.getSession();
HibernateUtil.beginTransaction();
try{
session.save(header);
}
catch (HibernateException e){
System.out.println("HibernateException " + e.getMessage());
}
HibernateUtil.commitTransaction();
HibernateUtil.closeSession();
System.out.println("Completed!");
}

}

SQL generate by hibernate:
Hibernate: insert into poheader (PO_NUMBER, DOC_DATE, DOC_TYPE, PURCH_ORG, PUR_GROUP, VENDOR) values (?, ?, ?, ?, ?, ?)
Hibernate: insert into poitem (PO_ITEM, MATERIAL, PLANT, STORE_LOC, NET_PRICE, DELIV_DATE, QUANTITY, PO_NUMBER) values (?, ?, ?, ?, ?, ?, ?, ?)
Hibernate: insert into poitem (PO_ITEM, MATERIAL, PLANT, STORE_LOC, NET_PRICE, DELIV_DATE, QUANTITY, PO_NUMBER) values (?, ?, ?, ?, ?, ?, ?, ?)

Which concrete implemented class you are using now?I propose that you use LinkedHashSet in your Parent class.

hi amjn
Actually I use HashSet in Poheader(parent).

The code looks like following:
public class Poheader implements Serializable
{
private Set poitems = new HashSet();

/**
* Simple constructor of Poheader instances.
*/
public Poheader()
{
}

..................... omit some code
......................
public void setPoitems(Set poitems){
this.poitems = poitems;
}

public Set getPoitems(){
return poitems;
}

public void add(Poitem poitem){
poitem.setPoheader(this);
poitems.add(poitem);
}

}

HashSet is out-of-order,and with a backing HashMap structure.
LinkedHashSet always keeps up insertion order.
TreeSet arranges objects by compareTo() of contained objects.

So you should select LinkedHashSet.

Hi amjn
Thank you for your help. I've solved problem after I use LinkedHashSet.