How to order a collection property ?

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

I have a property that is a collection.

I mapped it so as to order it by the listOrder index, like:

Code:

        <set name="links" inverse="true" order-by="list_order">
            <key>
                <column name="category_id" />
            </key>
            <one-to-many class="com.thalasoft.learnintouch.core.domain.Link" />
        </set>

The full Hibernate mapping is:

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Apr 18, 2010 1:03:51 PM by Hibernate Tools 3.2.1.GA -->
<hibernate-mapping>
    <class name="com.thalasoft.learnintouch.core.domain.LinkCategory" table="link_category" dynamic-insert="true" dynamic-update="true">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="identity" />
        </id>
        <version name="version" type="int">
            <column name="version" not-null="true" />
        </version>
        <property name="name" type="string">
            <column name="name" length="50" not-null="true" />
        </property>
        <property name="description" type="string">
            <column name="description" not-null="false" />
        </property>
        <set name="links" inverse="true" order-by="list_order">
            <key>
                <column name="category_id" />
            </key>
            <one-to-many class="com.thalasoft.learnintouch.core.domain.Link" />
        </set>
    </class>
</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Apr 18, 2010 1:03:51 PM by Hibernate Tools 3.2.1.GA -->
<hibernate-mapping>
    <class name="com.thalasoft.learnintouch.core.domain.Link" table="link" dynamic-insert="true" dynamic-update="true">
        <id name="id" type="java.lang.Integer">
            <column name="id" />
            <generator class="identity" />
        </id>
        <version name="version" type="int">
            <column name="version" not-null="true" />
        </version>
        <property name="name" type="string">
            <column name="name" length="50" not-null="true" />
        </property>
        <property name="description" type="string">
            <column name="description" />
        </property>
        <property name="image" type="string">
            <column name="image" length="50" />
        </property>
        <property name="url" type="string">
            <column name="url" />
        </property>
        <property name="listOrder" type="int">
            <column name="list_order" not-null="true" />
        </property>
        <many-to-one name="linkCategory" class="com.thalasoft.learnintouch.core.domain.LinkCategory" fetch="select">
            <column name="category_id" />
        </many-to-one>
    </class>
</hibernate-mapping>

I coded a test to make sure the property is retrieved in a correct order, that is, is ordered by the listOrder index:

Code:

   @Test
   public void testCollection() {
      link0 = new Link();
      link0.setName("Thalasoft");
      link0.setImage("image0.png");
      link0.setListOrder(3);
      linkCategory0.addLink(link0);
      link1 = new Link();
      link1.setName("Libe");
      link1.setImage("image1.jpg");
      link1.setListOrder(2);
      linkCategory0.addLink(link1);
      link2 = new Link();
      link2.setName("Google");
      link2.setImage("image2.gif");
      link2.setListOrder(1);
      linkCategory0.addLink(link2);
      LinkCategory linkCategory = linkCategoryDao.findById(linkCategory0.getId(), false);
      assertEquals(3, linkCategory.getLinks().size());
      assertEquals(link2.getName(), linkCategory.getLinks().iterator().next().getName());
      assertEquals(link1.getName(), linkCategory.getLinks().iterator().next().getName());
      assertEquals(link0.getName(), linkCategory.getLinks().iterator().next().getName());
   }

But when running the test it retrieves the collection in a random order, different every build, ignoring the listOrder index:

Quote:

org.junit.ComparisonFailure: expected:<[Google]> but was:<[Thalasoft]>

If lucky, sometimes the test succeeds, only to fail on the next build.

Of course, I need the database itself to order the collection items.

I read the part on sorted collections at http://docs.jboss.org/hibernate/core/3. ... tions.html specifically:

"If you want the database itself to order the collection elements, use the order-by attribute of set, bag or map mappings.".

But could not see the solution.

Any clue ?

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

A funny thing is that if I use a dummy non existing property name as in:

order-by="dummylist_order"

the mapping is still loaded fine, the test failing but not being in error.

Looks like my attribute order-by="list_order" is simply ignored.

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

Here is the bean property:

Code:

private SortedSet<Link> links = new TreeSet<Link>();

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

Correct me if I'm wrong but I understand now that a table with a column acting as an index to sort the rows, must be mapped as a List and not as a Set.

So, I'm now trying the following mapping:

Code:

        <list name="links" inverse="true">
            <key column="category_id" />
            <list-index column="list_order" />
            <one-to-many class="com.thalasoft.learnintouch.core.domain.Link" />
        </list>

with the bean property being:

Code:

private List<Link> links = new LinkedList<Link>();

and the test:

Code:

   public void testCollection() {
      link0 = new Link();
      link0.setName("Thalasoft");
      link0.setImage("image0.png");
      link0.setListOrder(3);
      linkCategory0.addLink(link0);
      link2 = new Link();
      link2.setName("Google");
      link2.setImage("image2.gif");
      link2.setListOrder(1);
      linkCategory0.addLink(link2);
      link1 = new Link();
      link1.setName("Libe");
      link1.setImage("image1.jpg");
      link1.setListOrder(2);
      linkCategory0.addLink(link1);
      LinkCategory linkCategory = linkCategoryDao.findById(linkCategory0.getId(), false);
      assertEquals(3, linkCategory.getLinks().size());
      assertEquals(link2.getName(), linkCategory.getLinks().get(0).getName());
      assertEquals(link1.getName(), linkCategory.getLinks().get(1).getName());
      assertEquals(link0.getName(), linkCategory.getLinks().get(2).getName());
   }

But I still get the collection items not ordered:

Quote:

org.junit.ComparisonFailure: expected:<[Google]> but was:<[Thalasoft]>

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

By the way, here is the method to add a link to a category:

Code:

   public List<Link> getLinks() {
      return this.links;
   }

   @SuppressWarnings("unused")
   private void setLinks(List<Link> links) {
      this.links = links;
   }

   public void addLink(Link link) {
      LinkCategory currentCategory = link.getLinkCategory();
      if (currentCategory != this) {
         if (currentCategory != null) {
            currentCategory.getLinks().remove(link);
         }
         link.setLinkCategory(this);
         this.links.add(link);
      }
   }

chirag.naikec · **Posted:** Wed Dec 22, 2010 2:59 am

I dont know what's the exact answer..But i can suggest something..why dont you add criteria.orderBy to your criteria while creating criteria in business class.

May be this can help you.

Chirag

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

Hi Chirag,

Thanks for your comment, but which statement should I add the order by clause to ?

The thing is, the collection is a property of an entity. The entity is retrieved by a regular findById in the generic Dao.

There is no such statement to retrieve the collection. It is retrieved alongside the entity. And lazily.

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

Any one ? It should be a fairly common problem, a collection property with its own index..

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

Must be the Christmas break..

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

I modified the Hibernate mapping to add a cascade attribute:

Code:

        <list name="links" inverse="true" cascade="persist,merge,save-update">
            <key column="category_id" not-null="true" />
            <list-index column="list_order" base="1" />
            <one-to-many class="com.thalasoft.learnintouch.core.domain.Link" />
        </list>

but I still get the same exception:

Quote:

org.junit.ComparisonFailure: expected:<[Google]> but was:<[Thalasoft]>

I then added a flush() in the test:

Code:

      linkCategoryDao.flush();
      LinkCategory linkCategory = linkCategoryDao.findById(linkCategory0.getId(), false);
      assertEquals(3, linkCategory.getLinks().size());

but I again get the same exception:

Quote:

org.junit.ComparisonFailure: expected:<[Google]> but was:<[Thalasoft]>

This leads me to wonder if the ordering is not simply ignored by Hibernate.

Indeed, the ordering is specified using, not a bean property name, but a database column name:

Code:

<list-index column="list_order" base="1" />

Also, in my test case, the log shows all 5 insert statements, 3 for the links and 2 for the link categories. But it does not show any sql statement corresponding to the select of the findById method. Why is that ?

If the beans are cached and never actually persisted into the database itself, then is Hibernate still doing the ordering ?

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

How come there is not one post on the forum with the list-index keyword ?

search.php?keywords=list-index&terms=all&author=&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

I again tried with a Set instead of a List, this time like:

Code:

        <set name="links" inverse="true" order-by="list_order" cascade="all-delete-orphan">
            <key column="category_id" />
            <one-to-many class="com.thalasoft.learnintouch.core.domain.Link" />
        </set>

and

Code:

private Set<Link> links = new LinkedHashSet<Link>();

But it did not help and the error was still:

Quote:

org.junit.ComparisonFailure: expected:<[Google]> but was:<[Thalasoft]>

johnjames1985 · **Joined:** Tue Dec 28, 2010 6:31 pm **Posts:** 1

thanks for this, really helped me

cheers

stephaneeybert · **Joined:** Mon Apr 16, 2007 8:10 am **Posts:** 246

Do you mean you solved the same issue ?

I still haven't solved it..

pasindu.slva · **Joined:** Wed Dec 29, 2010 11:20 am **Posts:** 1

Hi,

Try <set name="links" inverse="true" order-by="list_order asc">