Hi,
I have a problem when mapping an entity, containing a collection of value
objects, where the collection has map-semantics, and each value object
(composite element) have a reference to another entity that is also used as the
key of the collection.
EntityRoot: Entity with collection of value objects
ValueObjectChild: Value object with reference to EntityKey
EntityKey: Other entity used as key in indexed collection of an EntityRoot
object.
The question is: Is it possible to both use the other entity (EntityKey) as the
key of collection elements, and as the target of a many-to-one association for
each value of collection elements, without having two separate FK columns in
the link table in the database?
Okay lets see some code and mappings….Lets start with mappings
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
assembly="FirstSolution"
namespace="FirstSolution.Domain">
<class name="EntityRoot">
<id name="Id">
<generator
class="hilo"/>
</id>
<map name="Children"
cascade="save-update" access="field.camelcase-underscore">
<key
column="EntityRoot_Id"/>
<index-many-to-many column="EntityKey_Id" class="EntityKey"/>
<composite-element class="ValueObjectChild">
<!--
How can I map a reference to the same entity used as key for this
collection of
values without having two FK constraints (that is using the same FK
column-name
as used in the index-many-to-many declaration)????
-->
<many-to-one name="KeyEntity" not-null="true"/> <-- Have to use this
one, but creates a duplicate FK
<!--
The following uncommented line will generate a throw of:
'MappingException : Repeated column in mapping for
collection:....'
-->
<!--<many-to-one name="KeyEntity" column="EntityKey_Id"
not-null="true"/>--> <-- would like this, to reuse FK, and have reference and
key point to identical entities
<property name="Qty" not-null="true"/>
</composite-element>
</map>
</class>
<class name="EntityKey">
<id name="Id">
<generator
class="hilo"/>
</id>
</class>
</hibernate-mapping>
Kind regards
Maxild
P.S.
The classes are not that interesting, but here they are for completeness
namespace FirstSolution.Domain
{
public class EntityKey : EntityBase<EntityKey, long>
{
}
public class EntityRoot : EntityBase<EntityRoot, long>
{
private readonly
IDictionary<EntityKey, ValueObjectChild> _children;
public virtual
IEnumerable<ValueObjectChild> Children
{
get { return
_children.Values; }
}
public virtual void
Add(ValueObjectChild child)
{
_children.Add(child.KeyEntity, child);
}
}
public class ValueObjectChild :
IEquatable<ValueObjectChild>
{
protected ValueObjectChild() {}
public ValueObjectChild(EntityKey
other)
{
if (other ==
null)
{
throw new ArgumentNullException("other");
}
KeyEntity =
other;
}
public virtual bool
Equals(ValueObjectChild other)
{
if (other ==
null) return false;
return
other.KeyEntity.Equals(KeyEntity);
}
public virtual EntityKey KeyEntity
{ get; private set; }
public virtual int Qty { get; set; }
}
}
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