I am having difficulty retrieving a sorted set. Before using Hibernate I would expect to receive the rows of the database back in the order they were stored (usually sequential by ID). I have found that when using sets the order in which objects are returned is quite random. In the "mostly" full mapping below I have added the sort="natural", which then gives the error listed. without sort="natural" the mapping works fine, except that the objects are always in some random order.

How can I map a sorted set? I have searched the forum with no luck. I also have hibernate in action which gives examples using collections of Strings. Does the method change when I am retrieving objects other than string??? Thanks in advance...

Hibernate version: 2.1.6

Mapping documents:
<hibernate-mapping package="org.simplecart.shopcart.model">

<class name="CatalogItem"
table="CATALOG_ITEM">

<id name="id"
type="long"
column="CATALOG_ID"
unsaved-value="null">
<generator class="native"/>
</id>

<property name="name"
type="string"
column="NAME"
length="255"/>

<property name="description"
type="text"
column="DESCRIPTION"/>

<joined-subclass
name="Product"
table="PRODUCT">
<key column="PRODUCT_ID"/>

<many-to-one
name="category"
class="Category"
column="CATEGORY_ID"
cascade="save-update"/>

</joined-subclass>

<joined-subclass
name="Category"
table="CATEGORY">
<key column="CATEGORY_ID"/>

<set name="products"
table="PRODUCT"
inverse="true"
lazy="true"
cascade="save-update"
sort="natural">
<key column="CATEGORY_ID"/>
<one-to-many class="Product"/>
</set>

</joined-subclass>

</class>

</hibernate-mapping>

Partial stack trace of any exception that occurs:
net.sf.hibernate.LazyInitializationException: Failed to lazily initialize a collection

Name and version of the database you are using: PostgreSQL 7.4

I'll answer my own question:

I wrote a comparator for persistent classes


and I modified my mapping as follows:

<set name="products"
table="PRODUCT"
inverse="true"
lazy="true"
cascade="save-update"
sort="org.simplecart.shopcart.model.PrimaryKeyComparator">
<key column="CATEGORY_ID"/>
<one-to-many class="Product"/>
</set>

If sorting with a comparator, then the sorting is done in memory and not by the database.

Your collection is not a large one ?

In that case, a sorting by the database would make more sense.