NHibernate - Unable to save child entities - nhibernate

Question

This is supposed to be a simple 1-N relationship, however I am not able to save the children as NHibernate uses null as a value in the insert statement of the child.
public class Event
{
public virtual string Id { get; set; }
public virtual string Name { get; set; }
public virtual IList<EventParameter> Parameters{ get; set; }
public Event() { Parameters = new List<EventParameter>(); }
}
[Serializable]
public class EventParameter : Parameter
{
public virtual Event Event { get; set; }
public virtual string ComparisonMethod { get; set; }
public override bool Equals(object obj) {}
public override int GetHashCode() {}
}
The mappings are like this
public EventMapping()
{
Table(...);
Id(x => x.Id)
.Column(...)
.GeneratedBy
.Custom<global::NHibernate.Id.SequenceGenerator>(builder => builder.AddParam("sequence", "..."));
Map(x => x.Name).Column("Name").Length(100);
HasMany<EventParameter>(x => x.Parameters)
.KeyColumns.Add(...)
.Inverse()
.Cascade.All();
}
public EventParameterMapping()
{
Table(....);
CompositeId()
.KeyProperty(x => x.Event.Id, "...")
.KeyProperty(x => x.ParameterId, "...");
References(x => x.Event);
}
The Insert statement for the parent is correct, however for the child it is not.
INSERT INTO ...
(...columns...)
VALUES (..., null, ...)
Before this happens I get the following warning: Unable to determine if entity is transient or detached; querying the database. Use explicit Save() or Update() in session to prevent this.
I do use Save() in the transaction. Any ideas why this happens?

Answer 1

Solution here is suprisingly simply. We have to use inverse="true" mapping:
HasMany<EventParameter>(x => x.Children)
.KeyColumns.Add("...")
.Inverse()
.Cascade.All();
But, this is kind of optimization, which would require both sides of relation to be always properly set in our C# code:
var parent = ...;
var child = new Child();
// both sides MUST be set
parent.Children.Add(child);
child.Parent = parent;
Please, observe this for more details
Inverse = “true” example and explanation