@PeteA.
Yes, the index is part of the primary key. the database terms, Child is
what is called in database terms a dependent entity. Yes, children could be
deleted, but the only assumption you can make is that, for a given parent,
the Index is unique among children. In this particular case the order
doesn't matter.
I guess in my scenario, NH doesn't know whether the child object it's a new
one or not, and that's acceptable, even though logically it could mark the
children as new because their parent is new (which NH should not have a
problem detecting).
>From a database modeling point of view, it doesn't always make sense to
assign surrogate primary keys to dependent entities. The example that I
gave was simplified. In the real world the children of the parent are
description records in different languages of the parent. Instead of the
Index field I have a language code/country code, so the child key is made
of parentId/language code/country code. The language code and the country
code are Foreign Keys to a table that contains Cultures.
I still think that NH can mark the object as new if one of the FK objects
that is also PK field is new.
Thanks
On Monday, November 26, 2012 1:44:32 AM UTC-8, PeteA wrote:
>
> I suspect that you've not told NHibernate how to know that it's a new
> child (by way of the unsaved-value attribute. However, is it really true
> that the index is part of the child's PK as opposed to a UQ? My reading of
> the pseudo-code is that you've got a parent with an ordered list of
> children; is the order guaranteed immutable (including no deletes, ever!)
> and truly an identifier? If you ever delete or re-order children then I'd
> suggest that the child is promoted to a 'first class' entity with it's own
> ID. FWIW, when I have this situation my pattern tends to be:
>
>
>
> TChild:
>
> Parent {get;protected set;}
>
> Index { get { return Parent.Children.IndexOf(this); } }
>
> Child(Parent parent) {
>
> if(parent == null) throw;
>
> }
>
>
>
> /Pete
>
>
>
>
>
> *From:* [email protected] <javascript:> [mailto:
> [email protected] <javascript:>] *On Behalf Of *costa
> *Sent:* 23 November 2012 19:27
> *To:* [email protected] <javascript:>
> *Subject:* [nhusers] Re: How to save new entities with generated Guid
> without requiring a select from NH
>
>
>
> Hello:
>
> I have the same problem. I have two tables TParent/TChild where TChild is
> a dependent table, i.e.
>
> TParent:
> id (PK) - identity field (I am using Sql Server 2008)
> name
>
> TChild
> ParentId (PK1) -> TParent.Id
> Index (PK2)
> ...
>
> The combination ParentId/Index is unique.
>
>
>
> When I save the entities:
> I have something like this:
>
> var parent = new TParent();
> var child = new TChild();
> child.Index = 1;
> child.Parent = parent;
>
> parent.Children.Add(child);
>
> child = new TChild();
> child.Index = 2;
> child.Parent = parent;
>
> parent.Children.Add(child);
>
> Session.SaveOrUpdate(parent);
>
> When this runs, I get the warning:
>
> Unable to determine if ... with assigned identifier is transient or
> detached
>
> I run a sql trace and before NH executes the child inserts it executes
> select statements to see if the children are there.
>
> I am still using NH 3.1.0. I will upgrade to 3.3.1 soon, but I was curious
> why NH can't figure out that the children are new.
>
>
> Calling Session.Save(child) before saving the parent (and right after the
> child was added to the Children collection) doesn't seem to work because it
> fired the child inserts before the parent was created
>
>
> Thanks
>
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