Load parent without childs

chaessig · **Joined:** Tue Jan 16, 2007 5:42 am **Posts:** 4

Hello NHibernate users,

I have a newbie question.

I have a one-to-many relation between a parent and a child class.

There will be many childs for each parent. So, in my application, I would just show the parents, so that the application user can select the parent, and then get all childs of the selected parent ( through nhibernate ), to avoid loading of all childs of all parents.

So, my question is : how can I load the parents without loading the childs ?

Thanks in advance,

Christian

JWLato · **Joined:** Mon Apr 02, 2007 12:31 pm **Posts:** 19

If you use lazy initialization on the collection of child objects, they won't be loaded until they're accessed. In NHibernate 1.2, this is the default behavior. In earlier versions, add lazy="true" to the collection mapping.

You should check the documentation regarding lazy initialization and proxies since there are some restrictions imposed by their use. Most notable, the collection must be mapped as an interface (ISet, IList, etc) and not a class. Also, using lazy loading can cause problems with session management; if the session that loads the parent isn't available when you attempt to load the children you will get a LazyInitializationException if you don't attach the object to the new session.

jakeroerig · **Joined:** Thu Jan 20, 2005 3:03 pm **Posts:** 3

I have the same problem.

Quote:

Most notable, the collection must be mapped as an interface (ISet, IList, etc) and not a class.

When you say map the collection as an interface what do you mean exactly?

.ben · **Joined:** Tue May 02, 2006 8:04 am **Posts:** 34

The field which actually contains the list.

jakeroerig · **Joined:** Thu Jan 20, 2005 3:03 pm **Posts:** 3

Hi guys, no matter what I do my child collection gets loaded. Please help.

Parent mapping file:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" schema="mySchema">
   <class name="Domain.Parent, Domain" table="PARENT" persister="Server.Persistence.NHibernateWrapper.DomainPersister, Server.Persistence.NHibernateWrapper">
      <id name="Key" type="Guid" column="ParentKey">
         <generator class="assigned"/>
      </id>
    <version name="Version" column="Version" type="Int32" unsaved-value="null" />
      <property name="Name" column="Name" type="String"/>
      <bag name="Children" lazy="true" access="Server.Persistence.NHibernateWrapper.Accessor, Server.Persistence.NHibernateWrapper">
         <key column="ParentKey" />
         <one-to-many class="Domain.Child, Domain" />
      </bag>
   </class>
</hibernate-mapping>

Child mapping file:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0" schema="mySchema">
   <class name="Domain.Child, Domain" table="CHILD" lazy="true" persister="Server.Persistence.NHibernateWrapper.DomainPersister, Server.Persistence.NHibernateWrapper">
      <id name="Key" type="Guid" column="ChildKey">
         <generator class="assigned"/>
      </id>
    <version name="Version" column="Version" type="Int32" unsaved-value="null" />
      <property name="Name" column="Name" type="String"/>    
   </class>
</hibernate-mapping>

Parent class:

Code:

namespace Domain
{
   [Serializable()]
    public class Parent : IDomain
   {
      private Guid key = new Guid();        
        private string name;
        private int? version;
        private DomainCollection<Child> children;

      public Parent()
        { }
      
        public string Name
        {
            get { return name; }
            set { name = value; }
        }

        public virtual int? Version
        {
            get
            {
                return version;
            }
            set
            {
                version = value;
            }
        }

        public virtual Guid Key
        {
            get
            {
                return key;
            }
            set
            {
                key = value;
            }
        }

        public DomainCollection<Child> Children
      {
         get { return children; }
            set { children = value; }
      }
    }
}

Child class:

Code:

namespace Paceart.Domain
{
   [Serializable()]
   public class Child : IDomain
   {
        private Guid key = new Guid();        
        private string name;
        private int? version;

public Child()
      { }

        public virtual string Name
        {
            get { return name; }
            set { name = value; }
        }

        public virtual int? Version
        {
            get
            {
                return version;
            }
            set
            {
                version = value;
            }
        }

        public virtual Guid Key
        {
            get
            {
                return key;
            }
            set
            {
                key = value;
            }
        }
    }
}

.ben · **Joined:** Tue May 02, 2006 8:04 am **Posts:** 34

I don't know if it's because of the persister.

And how do you know the children are being loaded? If you 'hit' the property you will trigger the lazy initialization.

jakeroerig · **Joined:** Thu Jan 20, 2005 3:03 pm **Posts:** 3

Thanks, .ben. I think it is because of the persister. I took that out and ran it again, now I get a lazy exception.

I was using the SQL Profiler to verify it was loading the children.

I guess I'll dig into the persister.