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adcworks
 Post subject: How to set a collection count without new property
PostPosted: Tue Jul 13, 2004 10:25 am 
Senior
Senior

Joined: Fri Jun 18, 2004 10:17 am
Posts: 140
I have a situation where I load a list of Schedule objects and each Schedule contains a Set of ScheduleUpdate objects. On my list page I only ever need to show the title, last created date and number of updates in the set belonging to the Schedule.

I was finding my list page quite slow as it is loading everything out including the ScheduleUpdate objects and sometimes just 1 Schedule has 25 of these.

Therefore I decided to restrict the amount brought back by Hibernate with a scalar query (shown in Java Code below).

I have however found a shortcoming of either Hibernate OR my knowledge ;) Basically my scalar query counts the updates available for the Schedule, but I have no property defined to store this numeric value into the Schedule object. I do not want to have to create another object which is just a stripped down version of Schedule and includes the count as that would be a little inefficient I think ... I would rather reuse a mainly nulled Schedule.

Can anyone suggest what the best thing to do might be for this situation? Do I need a stripped down Schedule? Do I need to add a new property to Schedule? Can I just add a new class member to Schedule WITHOUT adding it to the Schedule mapping file for persistence?

THANKS!

Hibernate
======

2.1

Mapping
=====

Code:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping
    PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>

    <class name="com.qas.newmedia.intranet.iq.dto.schedules.Schedule" table="Schedules">

        <id name="id" type="int" column="schedule_id" unsaved-value="0">
           <generator class="identity" />
       </id>
            
        <property name="owner" column="owner" not-null="false" />
      <property name="associates" column="associates" not-null="false" />
      <property name="status" column="status" not-null="false" />
      <property name="title" column="title" not-null="true" />
      <property name="summary" column="summary" not-null="false" />
      <property name="description" column="description" not-null="false" />
      <property name="created" type="date" column="created" not-null="false" />
      <property name="lastUpdated" type="date" column="last_updated" not-null="false" />
      
      <set name="updates" order-by="created desc">
            <key column="schedule_id"/>
            <one-to-many class="com.qas.newmedia.intranet.iq.dto.schedules.ScheduleUpdate"/>
        </set>
      
      <set name="links" order-by="created desc">
            <key column="schedule_id"/>
            <one-to-many class="com.qas.newmedia.intranet.iq.dto.schedules.ScheduleLink"/>
        </set>
      
      <!--
        - Product Schedule
        -->
      
      <joined-subclass
         name="com.qas.newmedia.intranet.iq.dto.schedules.ProductSchedule"
         table="ProductSchedules">
         
           <key column="schedule_id" />
         
         <property name="developmentSignoff" type="date" column="development_signoff" not-null="false" />
         <property name="developmentSignoffFormat" column="development_signoff_format" not-null="false" />
         <property name="qatSignoff" type="date" column="qat_signoff" not-null="false" />
         <property name="qatSignoffFormat" column="qat_signoff_format" not-null="false" />
         <property name="launch" type="date" column="launch" not-null="false" />
         <property name="launchFormat" column="launch_format" not-null="false" />
       </joined-subclass>
      
      <!--
        - QA For Schedule
        -->      
      
      <joined-subclass
         name="com.qas.newmedia.intranet.iq.dto.schedules.QAForSchedule"
         table="QAForSchedules">
         
           <key column="schedule_id" />
         
         <property name="developmentSignoff" type="date" column="development_signoff" not-null="false" />
         <property name="developmentSignoffFormat" column="development_signoff_format" not-null="false" />
         <property name="qatSignoff" type="date" column="qat_signoff" not-null="false" />
         <property name="qatSignoffFormat" column="qat_signoff_format" not-null="false" />
         <property name="launch" type="date" column="launch" not-null="false" />
         <property name="launchFormat" column="launch_format" not-null="false" />
       </joined-subclass>            

      <!--
        - Data Acquisition Schedule
        -->

      <joined-subclass
         name="com.qas.newmedia.intranet.iq.dto.schedules.DataAcquisitionSchedule"
         table="DataAcquisitionSchedules">
         
           <key column="schedule_id" />
         
         <property name="productRelease" column="product_release" not-null="false" />
       </joined-subclass>
      
      <!--
        - Project Schedule
        -->      
      
      <joined-subclass
         name="com.qas.newmedia.intranet.iq.dto.schedules.ProjectSchedule"
         table="ProjectSchedules">
         
           <key column="schedule_id" />
         
         <property name="approval" type="date" column="approval" not-null="false" />
         <property name="targetCompletion" type="date" column="target_completion" not-null="false" />
       </joined-subclass>            

    </class>
   
   <class name="com.qas.newmedia.intranet.iq.dto.schedules.ScheduleUpdate" table="ScheduleUpdates">

        <id name="id" type="int" column="update_id" unsaved-value="null">
           <generator class="identity" />
       </id>

      <property name="created" type="date" not-null="true" />
      <property name="author" column="author" not-null="true" />
      <property name="comment" column="comment" type="text" length="4096" not-null="true" />
      <property name="internal" column="internal" type="boolean" />
         
   </class>
   
   <class name="com.qas.newmedia.intranet.iq.dto.schedules.ScheduleLink" table="ScheduleLinks">

        <id name="id" type="int" column="link_id" unsaved-value="null">
           <generator class="identity" />
       </id>

      <property name="created" type="date" not-null="true" />
      <property name="label" column="label" not-null="true" />
      <property name="link" column="link" not-null="true" />
         
   </class>   

</hibernate-mapping>



Java Code
=======

Code:

Session session = HibernateUtil.currentSession();
           Transaction tx = session.beginTransaction();
                       
            Iterator results = session.iterate(
               "select s.id, s.title, s.status, count(elements(s.updates)) " +
               "from " + type + " s group by s.id, s.title, s.status"
         );
                     
            while(results.hasNext()) {
                Object[] row = (Object[]) results.next();
                Schedule schedule = new Schedule();
                schedule.setId(((Integer) row[0]).intValue());
                schedule.setTitle((String) row[1]);
                schedule.setStatus((String) row[2]);
                //scheduleRow.setNumUpdates(((Integer) row[3]).intValue());
                list.add(schedule);
            }
           
            tx.commit();



Stack
====

N/A

DB
==

SQLServer 2000

Hibernate Log
=========

select productsch0_.schedule_id as x0_0_, productsch0__1_.title as x1_0_, productsch0__1_.status as x2_0_, count(updates1_.update_id) as x3_0_ from ProductSchedules productsch0_ inner join Schedules productsch0__1_ on productsch0_.schedule_id=productsch0__1_.schedule_id, ScheduleUpdates updates1_ where productsch0_.schedule_id=updates1_.schedule_id group by productsch0_.schedule_id , productsch0__1_.title , productsch0__1_.status
[/code]
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michael
 Post subject:
PostPosted: Tue Jul 13, 2004 10:31 am 
Hibernate Team
Hibernate Team

Joined: Tue Sep 09, 2003 2:10 pm
Posts: 3246
Location: Passau, Germany
One possibility would be to create a new object and to use the select new syntax:

Code:
select new StatusListItem(s.id, s.title, s.status, count(elements(s.updates))) from StatusItem s group by s.id, s.title, s.status


Another, IMHO nicer way would be to define the status collection as lazy, and use a collection filter to get the count:

Code:
StatusItem s = session.find("from StatusItem").get(0);
int updateCount = ( (Integer) s.createFilter( s.getUpdates(), "select count(*)" ).iterate().next() ).intValue();
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adcworks
 Post subject:
PostPosted: Tue Jul 13, 2004 10:43 am 
Senior
Senior

Joined: Fri Jun 18, 2004 10:17 am
Posts: 140
I need to send a List of Schedule objects to my UI so I can iterate over them nicely using JSTL or similar. Therefore each object in the List should ideally only have the properties I require including the count.

I tried out adding a new class member called numUpdates to the Schedule object and this modified version of my load method then works and it is noticeably faster. I do not add numUpdates as a property to my HBM. It also means only 1 HQL statement whereas I think your version does quite a few calls.

I don't think I understand your suggestions too well especially since I do not use an object called StatusListItem but I also cannot see how it is more efficient...

What do you think of what I have done with numUpdates?

Code:
public List load(String type, String orderBy, String orderDir)
      throws SchedulesException {
      
      List list = new ArrayList();;
       
        try {
           Session session = HibernateUtil.currentSession();
           Transaction tx = session.beginTransaction();
           
            Iterator results = session.iterate(
               "select s.id, s.title, s.status, s.lastUpdated, count(elements(s.updates)) " +
               "from " + type + " s " +
            "group by s.id, s.title, s.status, s.lastUpdated " +
               "order by " + orderBy + " " + orderDir
         );
                     
            while(results.hasNext()) {
                Object[] row = (Object[]) results.next();
               
                Schedule schedule = new Schedule();
                schedule.setId(((Integer) row[0]).intValue());
                schedule.setTitle((String) row[1]);
                schedule.setStatus((String) row[2]);
                schedule.setLastUpdated((Date) row[3]);
                schedule.setNumUpdates(((Integer) row[4]).intValue());
               
                list.add(schedule);
            }
           
            tx.commit();
        }
        catch (HibernateException hE) {
           throw new SchedulesException(hE.getMessage());
        }
       
        return list;

   }
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