How to save a child with assigned id in nhibernate

Question

I have two classes:

public class Parent
{
    public virtual long? ID { get; set; } // native
    public virtual IList<Child> Children { get; set; }
    public virtual string Name { get; set; }
}

public class Child
{
    public virtual long ID { get; set; } // assigned
    public virtual string Name { get; set; }
}

Instantiating and saving parent and child:

child = new Child() { ID = 1, Name = "SomeName" };
parent = new Parent() { Children = new List() { child } };
session.Save(parent);

Which gives me:

NHibernate.StaleStateException: Unexpected row count: 0; expected: 1.

I think the problem is with the assigned id on the child. Since it has an id, NHibernate thinks it has previously saved before which is not the case.

The generated (trimmed & renamed) SQL is:

NHibernate: select child0_.ID as child1_1_, child0_.NAME as NAME1_, child0_.PARENT_ID as COMMAND7_1_, from CHILD child0_
NHibernate: select parent0_.PARENT_ID as parent1_10_
NHibernate: select parent0_.PARENT_ID as parent1_10_, parent0_.NAME as parent2_10_ from PARENT parent0_
NHibernate: UPDATE CHILD SET PARENT_ID = @p0 WHERE CHILD_ID = @p1;@p0 = 2, @p1 = 1

Mapping files:

<class name="MyNamespace.Child" table="CHILD">
  <id name="ID" column="CHILD_ID" type="System.Int64">
    <generator class="assigned"></generator>
  </id>
  <property name="Name" column="NAME"></property>
</class>

<class name="MyNamespace.Parent" table="PARENT">
  <id name="ID" column="PARENT_ID" type="System.Int64">
    <generator class="native"></generator>
  </id>
  <property name="Name" column="NAME"></property>
  <bag name="Children">
    <key column="PARENT_ID"></key>
    <one-to-many class="MyNamespace.Child"></one-to-many>
  </bag>
</class>

While searching google, I found about version tag which may be a solution but I do not have a persistent field to use as version. In this case, how can I save (insert) a child with assigned id and its parent?

Answer 1

When cascading from a parent to a child, NHibernate uses the SaveOrUpdate method. You are correct that NHibernate need some way to determine whether it should perform an insert or an update. It will look at three different fields for an unsaved value to determine if the entity is new.

1. Id
2. Version
3. Timestamp

With an assigned Id, you will need either a Version or Timestamp field in order to indicate that the entity is new.

An alternative would be to call Save() on the children explicitly.