Hi guys,
My goal is to represent & map the following scenario using NHibernate:
public class Person {
private int _id;
private string _name;
public int ID { get {return _id;} set {_id = value;} }
public string Name { get {return _name;} set {_name = value;} }
}
A table representing Person
CREATE TABLE Person(
Id int NOT NULL,
Name nvarchar(20) default NULL ) ;
A table representing a many to many relation between one Person to another:
CREATE TABLE PersonRelations(
PersonId1 int NOT NULL,
PersonId2 int NOT NULL,
TypeOfRelation nvarchar(20) NOT NULL default 'Friend') ;

======================================
Initially I added a Collection of Person to the Person class:
private IList<Person> _relatedPersons;
public IList<Person> RelatedPersons
{
get { return _relatedPersons; }
set { _relatedPersons = value; }
}

My mapping currently looks like this:

Code:

<class name="Person" table="Persons">
    <id name="Id">
        <column name="ID" />
        <generator class="assigned" />
    </id>
    <property name="Name" />

    <bag name="RelatedPersons" table="personrelations">
        <key column="PersonId1" />
        <many-to-many class="Person" column="PersonId2" />
    </bag>
</class>

This mapping Is ok if I ignore the TypeOfRelation mentioned earlier. It saves the relation in personrelations table and deletes it when a person is deleted.

The problem is me not being able to answer the following question:
Who are John Doe's friends?
I basically need to load a person with a name "John Doe" and in some way define an expression on the relation table, thus getting in the RelatedPersons collection only the persons that relate to him with "Friend" as the type of relation.

There is very little / almost no documentation on this subject.
After a very long search in the forums, Google & nhibernate blogs, I found only one thread that discusses the issue of mapping many-to-many relations of the same class. (ttp://forum.hibernate.org/viewtopic.php?t=969967&start=0&postdays=0&postorder=asc&highlight=)
The above post only scrapes the surface of this subject, but not enough to answer my question.

Is there A way to do This?
Shaul

One suggestion of the top of the head: Introduce a Class representing your relation between persons

class Relation{
public string Type{...}
public Person RelatedTo{...}
public Person Person{...}
}

Then let each person have a bag of Relation classes

You problem is that you have data in the association, in many cases you can use a <map> and have it in a dictionary but as i understand your Model both the same "RelationType" and Person can appear in the collection multiple times for instance:

Person1 Friend
Person1 Coworker
Person2 Friend

so you would have problem using either as a key in a dictionary

I could create a class like you suggested, but that's like saing Relation is a type when it's actualy an association with propertie/s, moreover it'll force me to perform the association in the application itself.

Any other ideas?

But what type should your "RelationType" property be in your model if you dont introduce somewhere the value can be?

You could make your collections a KeyValuePair<string, Person> but i don't know if that is possible and it isn't very pretty

Let's say I'll create a type "RelationType" that has two Person instances and a string property holding the relation type.
An often scenario in my application would be selecting a Person by some criterion, followed by selecting all persons related to him with say "Friend" type relation.

This means I'll have two queries:
1) Select the person from the table
2) Create an instance of "RelationType" and use the person found earlier in order to select the related objects.

Is this how you suggest I should do it?
Should "RelationType" hols an instance of Person or only a Person's ID (PK)?

Doesn't a simple query like following work? After applying a parameter "John Doe", of course.

A person has a collection of RelationType all the relation they have, when you fetch the person you can use either eager or lazy loading to get the list of relation, and you can use ISession.Filter to filter in them.