Many-to-one relationship do not delete orphan children.

[Jacob Madsen]

Hi all,

I can't see why the orphans doesn't get delete, when cascade is set to
"all" in the "many-to-one" xml-element.

I have this mapping of an aggregate entity (table test_aggregates) and
child entity (table test_reference_entities):

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-
access="property" auto-import="true" default-cascade="save-update"
default-lazy="false">
<class xmlns="urn:nhibernate-mapping-2.2" lazy="false"
mutable="true" name="TestAggregate, Tests, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=null" table="test_aggregates">
<id access="backfield" name="Id" type="System.Int64, mscorlib,
Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
<column name="id" />
<generator class="hilo">
<param name="max_lo">100</param>
</generator>
</id>
<many-to-one cascade="all"
class="Namic.Being.Framework.Tests.Database.TestReferenceEntity,
Namic.Being.Framework.Tests, Version=1.0.0.0, Culture=neutral,
PublicKeyToken=null" name="ReferenceEntity">
<column name="ReferenceEntity_id" />
</many-to-one>
</class>
</hibernate-mapping>


<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-
access="property" auto-import="true" default-cascade="save-update"
default-lazy="false">
<class xmlns="urn:nhibernate-mapping-2.2" lazy="false"
mutable="true" name="TestReferenceEntity, Tests, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=null" table="test_reference_entities">
<id access="backfield" name="Id" type="System.Int64, mscorlib,
Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
<column name="id" />
<generator class="hilo">
<param name="max_lo">100</param>
</generator>
</id>
</class>
</hibernate-mapping>


Cheers!

[Aaron Fischer]

cascade="all-delete-orphan"

[Sergej Koščejev]

On 30.7.2010 22:09, Aaron Fischer wrote:
> cascade="all-delete-orphan"
>
As far as I remember, orphan delete is only supported for collections.

Sergej

[Jacob Madsen]

Yes, "all-delete-orphan" is not an option.

Do someone know if delete orphan is even supported for many-to-one?

I am using version 2.1.2.4000.

[Diego Mijelshon]

Many-to-one doesn't have the concept of orphans (it doesn't make sense).

Valid cascade values are here: http://nhforge.org/doc/nh/en/index.html#mapping-declaration-manytoone

 
    Diego

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[Jacob Madsen]

Are you sure it doesn't make sense? Do you believe that its not be possible in real world domains that (many-to-one) child entities is replaced in the lifetime of the aggregate.

2010/8/2 Diego Mijelshon <di...@mijelshon.com.ar>

[Jacob Madsen]

Let me add this to the previous mail... I don't believe in allowing
nhibernate (infrastructure) within the borders of an aggregate.

On Aug 2, 9:38 am, Jacob Madsen <ja...@mungo.dk> wrote:
> Are you sure it doesn't make sense? Do you believe that its not be possible
> in real world domains that (many-to-one) child entities is replaced in the
> lifetime of the aggregate.
>
> 2010/8/2 Diego Mijelshon <di...@mijelshon.com.ar>
>
>
>
> > Many-to-one doesn't have the concept of orphans (it doesn't make sense).
> > Valid cascade values are here:
> >http://nhforge.org/doc/nh/en/index.html#mapping-declaration-manytoone
> >  <http://nhforge.org/doc/nh/en/index.html#mapping-declaration-manytoone>
>
> >     Diego
>
> > On Sun, Aug 1, 2010 at 17:16, Jacob Madsen <ja...@mungo.dk> wrote:
>
> >> Yes, "all-delete-orphan" is not an option.
>
> >> Do someone know if delete orphan is even supported for many-to-one?
>
> >> I am using version 2.1.2.4000.
>
> >> On Jul 30, 10:41 pm, Sergej Koščejev <sergey....@gmail.com> wrote:
> >> >   On 30.7.2010 22:09, Aaron Fischer wrote:> cascade="all-delete-orphan"
>
> >> > As far as I remember, orphan delete is only supported for collections.
>
> >> > Sergej
>
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[Diego Mijelshon]

I didn't understand your statement, but many-to-one is a parent-to-child relationship (i.e. the declaring entity depends on the referenced one).

Let's say I have three classes, Parent, ChildA and ChildB.

ChildA and ChildB have many-to-one references to Parent.

When setting a ChildA.Parent to null, how in the world do you expect to check if the Parent is "orphan"? By doing two selects (in ChildA and ChildB tables) and seeing if there are any records???
 
    Diego

[Diego Mijelshon]

Read: many-to-one is a child-to-parent relationship
 
    Diego

[Frans Bouma]

> Read: many-to-one is a child-to-parent relationship

I think calling it a parent-child relationship is not really helpful, it's more of a A-depends-on-B relationship, i.o.w.: it's a dependency, not a parent -> child relationship, as for example 'Order' in northwind has 2 m:1 relationships: with Customer and with Employee. Which one is the 'parent' ? Also in diamond shaped models, multiple dependency paths are visible, but on the node level it's not known which path is the real dependency.

FB

>
> Diego
>
>
>
> On Mon, Aug 2, 2010 at 09:06, Diego Mijelshon <di...@mijelshon.com.ar>
> wrote:
>
>
> I didn't understand your statement, but many-to-one is a parent-to-
> child relationship (i.e. the declaring entity depends on the referenced
> one).
>
> Let's say I have three classes, Parent, ChildA and ChildB.
> ChildA and ChildB have many-to-one references to Parent.
> When setting a ChildA.Parent to null, how in the world do you expect
> to check if the Parent is "orphan"? By doing two selects (in ChildA and
> ChildB tables) and seeing if there are any records???
>
> Diego
>
>
>
> On Mon, Aug 2, 2010 at 04:38, Jacob Madsen <ja...@mungo.dk> wrote:
>
>
> Are you sure it doesn't make sense? Do you believe that its
> not be possible in real world domains that (many-to-one) child entities is
> replaced in the lifetime of the aggregate.
>
>
>
> 2010/8/2 Diego Mijelshon <di...@mijelshon.com.ar>
>
>
> Many-to-one doesn't have the concept of orphans (it
> doesn't make sense).
> Valid cascade values are here:
> http://nhforge.org/doc/nh/en/index.html#mapping-declaration-manytoone

> <http://nhforge.org/doc/nh/en/index.html#mapping-
> declaration-manytoone>

>
> Diego
>
>
>
> On Sun, Aug 1, 2010 at 17:16, Jacob Madsen
> <ja...@mungo.dk> wrote:
>
>
> Yes, "all-delete-orphan" is not an option.
>
> Do someone know if delete orphan is even
> supported for many-to-one?
>
> I am using version 2.1.2.4000.
>
>
>
> On Jul 30, 10:41 pm, Sergej Koščejev
> <sergey....@gmail.com> wrote:
> > On 30.7.2010 22:09, Aaron Fischer wrote:>
> cascade="all-delete-orphan"
> >
> > As far as I remember, orphan delete is only
> supported for collections.
> >
> > Sergej
>
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[Diego Mijelshon]

Nitpicker ;-)

Point taken. 

he logic around it is still the same, regardless of how we call it. If A references/depends-on/is-a-child-of B, then it makes no sense to orphan B based on its relationship with A.
 
    Diego

2010/8/2 Frans Bouma <fr...@sd.nl>

[Frans Bouma]

> Nitpicker ;-)

:P

In ORM land, parent-child is already defined: for inheritance, so IMHO it's best not to overload it with an ambiguistic definition again. But it's hard though, many people still think that an FK constraint defines a parent-child relationship ;)

> Point taken.
> he logic around it is still the same, regardless of how we call it. If A
> references/depends-on/is-a-child-of B, then it makes no sense to orphan B
> based on its relationship with A.

indeed, as B is never an 'orphan' in the sense that it has a violating constraint. So I think the topic starter wants something else than what he discussed.

FB

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[Jacob Madsen]

It seems that I have misused the term "orphan" in context of nhibernate.

Imagine that I have (please ignore lazy load/virtual and so on):

public class A

{

    private B _b;

    public A()

    {

        _b = new B();

    }

    public void ChangeB(string input)

    {

        var b = new B(input);

        _b = b;

    }

}

How would you delete the old (what I called orphan before) _b from the database, when nhibernate / infrastructure should not be part of the aggregate?

[Diego Mijelshon]

Use a trigger.
 
    Diego

[Jacob Madsen]

Is there a nhibernate abstraction to triggers or will triggers force me to implicit depend on a specific database product?

[Fabio Maulo]

database-object

Fabio Maulo

[Jacob Madsen]

Hi Fabio,

I'm a bit unsure of what you mean by "database-object"?

[Diego Mijelshon]

http://nhforge.org/doc/nh/en/index.html#mapping-database-object
 
    Diego

2010/8/2 Jacob Madsen <ja...@mungo.dk>

[Fabio Maulo]

http://nhforge.org/doc/nh/en/index.html#mapping-database-object

You can create triggers and define the dialect-scope

2010/8/2 Jacob Madsen <ja...@mungo.dk>

--
Fabio Maulo

[Jacob Madsen]

Great help guys!

[jimbobmcgee]

A trigger will be part of your DDL; it is a database object that you
will create after creating your table.
So yes, it may be required to be different depending on the RDBM that
you use, but not much more so than your CREATE TABLE statements...

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