Question

A customer can have several contact. The code below is working but… the contacts for this customer are deleted first and after inserted again. Is not possible to avoid this delete and just insert the new one ?

<class name="Customer" table="Customer">
    <id name="Id">
        <generator class="native" />
    </id>
    <property name="LastName" not-null="true" />

    <bag name="Contacts" cascade="all-delete-orphan" table="CustomerContact">
        <key column="Customer" not-null="true" />
        <many-to-many class="Contact"/>
    </bag>l
</class>

<class name="Contact" table="Contact">
    <id name="Id">
      <generator class="native" />
    </id>
    <property name="LastName" not-null="true" />

    <many-to-one name="Customer" column="Customer" not-null="true" />
</class>

public virtual void AddContact(Contact contact)
{
    Contacts.Add(contact);
    contact.Customer = this;
}

When I do this code twice, to add 2 contacts :

Contact contact = new Contact() { LastName = "MyLastName" };
Customer customer = session.Get(customerId);
customer.AddContact(contact);
session.Update(customer);

Answer 1

You are using a bag for your collection, a bag can contain duplicates, does not maintain order and there is no way to identify an individual entry in the bag distinctly with SQL.

That is why NH removes and inserts all assigned entities. Use a set if it suits your requirements instead.