NHibernate. Can't add two child to parent

I have common parent\children scenario:

public class Order : AdvancedBaseOrder
{

    ICollection<ProducerRelation> producers = new List<ProducerRelation>();
    public virtual ICollection<ProducerRelation> Producers
    {
        get { return producers; }
        set { producers = value; }
    }
}

public class ProducerRelation : BaseProducerRelation
{
    public virtual Order Order { get; set; }
    public virtual int Number { get; set; }
}

Mappings:

Order.hbm.xml
....
<set name="Producers" cascade="all-delete-orphan" inverse="true">
  <key column="order_id"/>
  <one-to-many class="ProducerRelation,Avtobus66.Core"/>
</set>
....


ProducerRelation.hbm.xml
....
 <many-to-one name="Order" class="Order, Avtobus66.Core" column="order_id" cascade="none"/>
<property name="Number" >
  <column name="number"/>
</property>
....

When I run this code:

            Order order = (Order)session.Get(typeof(Order), 23);
            var a = new ProducerRelation();
            a.Number = 6;
            a.Order = order;

            var b = new ProducerRelation();
            b.Number = 7;
            b.Order = order;

            order.Producers.Add(a);
            order.Producers.Add(b);
            session.Merge(order);
            session.Flush();

only one of my children is added. I know, that nhibernate is "watching" the child collection for changes, but what I do wrong? Why nhib can't add two children?

SQL:

 NHibernate: SELECT ... WHERE this_.id = ?p0;?p0 = 2开发者_Python百科3
 NHibernate: INSERT INTO gb_avtobus66.ekbprint_producer_relation (producer_price, producer_price_clean, order_id, ekbprint_product_id, client_id, number) VALUES (?p0, ?p1, ?p2, ?p3, ?p4, ?p5);?p0 = 0, ?p1 = 0, ?p2 = 23, ?p3 = NULL, ?p4 = NULL, ?p5 = 6
 NHibernate: SELECT LAST_INSERT_ID()

I suspect it is because of the fact that you're using a set collection type. A set is an unordered collection that contains no duplicates. So likely it's looking at the two new children and thinks that the second one is a duplicate. Make sure you override Equals/GetHashcode to indicate what is a duplicate entry.

Use get instead of Load.... :)