Question

I ve got the following setup:

public class ParentEntity
{
   public ICollection<ChildEntity> {get; set; }
}

public class ChildEntity
{
   // do i need to the parent here?
}

I managed to save the ParentEntity and cascaded the save to the added child entities which were saved as well. But in the db table the ParentId reference of the child was set to allow NULL. When setting it to NOT NULL the save failes since the ParentId in the child table is NULL.

What’s happening there? 😉

When

Answer 1

You should map both sides of the relationship normally, and when you add a child to the parent’s collection, you should also set the parent property on the child. Normally you would achieve this by writing a method like this:

public void AddChild(ChildEntity child)
{
   this.Children.Add(child);
   child.Parent = this;
}

NHibernate persists the ParentId column in the Child table based on the mapped property in the ChildEntity class. The definition of the one-to-many relationship merely allows NHibernate to load the collection from the database based on values in this column