NHibernate bidirectional many-to-many association

Question

Hello. I have a class with following description:

public class Customer {
    public ISet<Client> Contacts { get; protected set;}
}

I want to map Contacts property onto following table:

CREATE TABLE user_contacts (
    user1 uuid NOT NULL,
    user2 uuid NOT NULL
)

I want it to map bidirectionally, i.e. when Customer1 added to Customer2's Contacts, Customer1's Contacts collection should contain Customer2 (maybe only after entity reload). How could I do that?

Update Sure I can map left-to-right and right-to-left sets and then combine then at runtime, but it'll... hmm... untasty... Is there other solution? Any way, thank you very match, FryHard!

Answer 1

Take a look at this link on what hibernate calls unidirectional many-to-many associations. In Castle ActiveRecord I make use of HasAndBelongsToMany links, but I am not sure how exactly it is mapped in nhibernate.

Though taking a look at your question a little deeper, it looks like you will be linking bidirectionally from customer to user_contacts, which could break the many-many link. I will play with an example and see what I can come up with.

An Export of the hbm files from ActiveRecord shows this

<?xml version="1.0" encoding="utf-16"?>
<hibernate-mapping  auto-import="true" default-lazy="false" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="urn:nhibernate-mapping-2.2">
  <class name="NHibernateMapping.Customer, NHibernateMapping" table="Customer" schema="dbo">
    <id name="Id" access="property" column="Id" type="Int32" unsaved-value="0">
      <generator class="identity">
      </generator>
    </id>
    <property name="LastName" access="property" type="String">
      <column name="LastName" not-null="true"/>
    </property>
    <bag name="ChildContacts" access="property" table="user_contacts" lazy="false">
      <key column="user1" />
      <many-to-many class="NHibernateMapping.Customer, NHibernateMapping" column="user2"/>
    </bag>
    <bag name="ParentContacts" access="property" table="user_contacts" lazy="false" inverse="true">
      <key column="user2" />
      <many-to-many class="NHibernateMapping.Customer, NHibernateMapping" column="user1"/>
    </bag>
  </class>
</hibernate-mapping>

ActiveRecord example:

[ActiveRecord("Customer", Schema = "dbo")]
public class Customer
{
    [PrimaryKey(PrimaryKeyType.Identity, "Id", ColumnType = "Int32")]
    public virtual int Id { get; set; }

    [Property("LastName", ColumnType = "String", NotNull = true)]
    public virtual string LastName { get; set; }

    [HasAndBelongsToMany(typeof(Customer), Table = "user_contacts", ColumnKey = "user1", ColumnRef = "user2")]
    public IList<Customer> ChildContacts { get; set; }

    [HasAndBelongsToMany(typeof(Customer), Table = "user_contacts", ColumnKey = "user2", ColumnRef = "user1", Inverse = true)]
    public IList<Customer> ParentContacts { get; set; }
}

Hope it helps!

Answer 2

Hi! I found this article... it may help you...

http://sdesmedt.wordpress.com/2006/10/21/nhibernate-part-5-mapping-techniques-for-aggregation-many-to-one-and-many-to-many-mapping/

Hope it helps!