Cascade="all-delete-orphan"

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

I have read all-delete-orphan would delete every orphaned child of the deleted object.
I understood it as the following:
In a parent child context, I have 3 objects, Adam, Peter and Claire. Peter is the child of Adam and Claire is the child of Peter.
If I delete Claire, Peter and Adam are still persistent. If I would delete Peter, only Adam would be still persistent. Does this make sense? Ok, now to my question:

If I delete Claire in my project, NHibernate deletes every single object, that is associated with Claire. I would expect only Claire to be deleted...

My Class:

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


namespace NewNHibernate
{
    public class Person
    {
        public virtual int _id { get; set; }
        public virtual String _name { get; set; }
        public virtual Person _parent { get; set; }
        public virtual IList<Person> Children { get; set; }

        public Person()
        { }

        public Person(String name, Person parent)
        {
            _name = name;
            _parent = parent;

            Children = new List<Person>();

            if (null != parent)
            {
                parent.Children.Add(this);
            }
        }

        public virtual bool IsRoot()
        {
            return null == _parent ? true : false;
        }

        public virtual Person GetRoot()
        {
            Person root = _parent;

            while (root._parent != null)
            {
                root = root._parent;
            }

            return root;
        }

        public virtual Person AddChild(Person child)
        {
            child._parent = this;
            Person ancestor = this;

            while (ancestor._parent != null)
            {
                ancestor._parent = ancestor._parent._parent;
            }

            ancestor.Children.Add(child);

            return child;
        }
    }
}

My mapping:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" auto-import="false">
<class name="NewNHibernate.Person, NewNHibernate">

    <id name="_id" column="id" type="int" unsaved-value="0">
      <generator class="identity" />
    </id>
    <property name="_name" column="name" type="string" not-null="true" unique="true" />

    <many-to-one name="_parent" column="parent" class="NewNHibernate.Person" cascade="all-delete-orphan"/>

    <bag name="Children" cascade="all-delete-orphan" inverse="true">
      <key column="parent" foreign-key="FK_Person_Children" />
      <one-to-many class="NewNHibernate.Person"/>
    </bag>
  
  </class>  
</hibernate-mapping>

My Program:

Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NHibernate;
using NHibernate.Cfg;

namespace NewNHibernate
{
    class Program
    {
        static void Main(string[] args)
        {
            Person Adam = new Person("Adam", null);
            Person Peter = new Person("Peter", Adam);
            Person Claire = new Person("Claire", Peter);

            Person Nathan = new Person("Nathan", null);
            Person Matt = new Person("Matt", Nathan);

            using (ISession session = OpenSession())
            {
                session.SaveOrUpdate(Claire);
                session.SaveOrUpdate(Matt);

                session.Flush();

                IList<Person> Peters;

                ICriteria crit = session.CreateCriteria(typeof(Person));
                crit.Add(NHibernate.Criterion.Expression.Eq("_name", "Peter"));
                IList<Person> p = crit.List<Person>();

                Console.WriteLine(p.First()._name);

                session.Delete(p.First());
                session.Flush();
            }
        }

        public static ISession OpenSession()
        {
            ISession session = null;

                try
                {
                    log4net.Config.XmlConfigurator.Configure();
                    Configuration cfg = new Configuration().Configure();
                    session = cfg.BuildSessionFactory().OpenSession();
                }
                catch(Exception ex)
                {
                    if (null != ex.InnerException)
                    {
                        Console.WriteLine(ex.InnerException.Message);
                    }
                    else
                    {
                        Console.WriteLine(ex.Message);
                    }
                    return null;
                }
            return session;
        }
    }
}

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

any ideas?

wolli · **Posted:** Tue Nov 17, 2009 6:49 am

You also cascade to the parent, that makes no sense here (at least for delete):

<many-to-one name="_parent" column="parent" class="NewNHibernate.Person" cascade="all-delete-orphan"/>

Remove the cascade or change it to something that does not cascade deletes.

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

ok,

I've removed the cascade.

Code:

<many-to-one name="Company" column="CompanyId" />

Now I'm getting a TransientObjectException on my last session.Flush().
Can you give me the right direction, again?

wolli · **Posted:** Tue Nov 17, 2009 7:26 am

Is there an inner exception or a meaningful message in the exception ?

wolli · **Posted:** Tue Nov 17, 2009 7:37 am

You have to remove the child from the parent by yourself (that's part of the business model, not part of the persistance layer).

p.First().Parent.Remove(p.First());
p.First().Parent = null;

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

ok, this was one of the issues, I was NHibernate evaluating for.
But what is then the meaning of cascade=all-delete-orphan?

I thought it would delete the children automatically, when I delete the parent!?

wolli · **Posted:** Tue Nov 17, 2009 8:34 am

Yes, but you said you were deleting the child (Claire), not the parent ! When you delete the parent, everything should work with cascade, but when you want to remove a child, you have to remove it from the parent's collection.

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

ok, that's right. Thank you. I have changed it and I am removing Claire form the children collection.
But I am still getting this error (references an unsaved transient instance).

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

I'm getting this error, becaus NHibernate does not save the parents of Claire. It only persists them if I save the cascade property, which I should delete first. So I am at the beginning again.

Just to clarify:
I want to create a bidirectional association. If I save a child, I want NHibernate to save the parents (the cascade attribute in my many-to-one tag in Person.hbm.xml).
I want NHibernate to delete all children, if I delete a parent node.

mosdev · **Joined:** Mon Nov 02, 2009 9:52 am **Posts:** 19

I got it!
I saved the cascade attribute in the many-to-one and wrote the following:

Code:

        static void Main(string[] args)
        {
            SavePersons();
            DeletePerson();
        }

        private static void SavePersons()
        {
            Person Adam = new Person("Adam", null);
            Person Peter = new Person("Peter", Adam);
            Person Claire = new Person("Claire", Peter);

            using (ISession session = OpenSession())
            {
                session.SaveOrUpdate(Claire);
            }
        }

        private static void DeletePerson()
        {
            using (ISession session = OpenSession())
            {
                ICriteria crit = session.CreateCriteria(typeof(Person));
                crit.Add(NHibernate.Criterion.Expression.Eq("_name", "Claire"));
                IList<Person> p = crit.List<Person>();

                Person first = p.First();
                first._parent.Children.Remove(first);
                first._parent = null;
                session.Delete(first);

                session.Flush();
            }
        }

        public static ISession OpenSession()
        {
            ISession session = null;

                try
                {
                    log4net.Config.XmlConfigurator.Configure();
                    Configuration cfg = new Configuration().Configure();
                    session = cfg.BuildSessionFactory().OpenSession();
                }
                catch(Exception ex)
                {
                    if (null != ex.InnerException)
                    {
                        Console.WriteLine(ex.InnerException.Message);
                    }
                    else
                    {
                        Console.WriteLine(ex.Message);
                    }
                    return null;
                }
            return session;
        }