Hi all
I've recently started to evaluate NHibernate and have a question regarding
implementation of one-many associations. Let's say we have
[ParentClass] Parent 1----* Children [ChildClass]
It seems to me that when considering an in-memory model only I would do
something like this
ParentClass
//01: Don't allow modification of the Children property
public ReadOnlyCollection<ChildClass> Children
{
get
{
return new List<ChildClass>(children).AsReadOnly();
}
}
//Internal method to keep parent in sync with children
internal void ChildAdded(ChildClass c)
{
children.Add(c);
}
//Internal method to keep parent in sync with children
internal void ChildRemoved(ChildClass c)
{
children.Remove(c);
}
ChildClass
public ParentClass Parent
{
get { return parent; }
set
{
//Ensure original parent no longer thinks it owns this child
if (Parent != null)
Parent.ChildRemoved(this);
parent = value;
//Ensure the new parent knows it does own the child
if (Pareng != null)
Parent.ChildAdded(this);
}
}
NHibernate In Action suggests the following
public void AddChild(ChildClass c)
{
Children.Add(c);
c.Parent = this;
}
Problems I have with this approach are
01: It depends upon the developer always using Parent.AddChild rather than
Parent.Children.Add or setting Child.Parent.
02: If a Child already belongs to a different Parent and we are changing the
association then I have a choice between
A: If the Child's existing parent is already loaded, leaving
OriginalParent.Children with this Child in the list, or
B: If I add code to first remove the Child from its existing Parent then
having to load OriginalParent when it is not needed
The OPF I am used to using will do all of this for me, it will update the
original Parent.Children *if* it is already loaded, if it is not already
loaded then there is no need as the association state is stored in the
child.
I'm a bit concerned that I have to choose between having out of sync data,
or having to load a Parent instance when it is not needed.
Any recommendations?
Pete
====
http://mrpmorris.blogspot.com
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