使用NHibernate的Child-Parent关系

Question

I'm trying to figure out how to make child-parent relationships using NHibernate. I have two classes Foo and Bar. Foo have a collection of Bars and Bar have reference to parent Foo.

public class Foo
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual List<Bar> Children { get; set; }  
}

public class Bar
{
    public virtual int Id { get; set; }
    public virtual string Description { get; set; }
    public virtual Foo Parent { get; set; }
}

The mapping of this classes are:

  <class name="Foo" table="foos">
    <id name="Id" column="id">
      <generator class="identity"/>
    </id>
    <property name="Name" column="name" />
    <set name="Children" inverse="true" lazy="true">
      <key column="fooId"/>
      <one-to-many class="Bar"/>
    </set>
  </class>

  <class name="Bar" table="bars">
    <id name="Id" column="id">
      <generator class="identity"/>
    </id>
    <property name="Description" column="description" />
    <many-to-one name="Parent" column="fooId"/>
  </class>

This is sesion factory creation:

if (_sessionFactory == null)
{
    var configuration = new Configuration();
    configuration.Configure();
    configuration.AddAssembly(typeof(Foo).Assembly);
    _sessionFactory = configuration.BuildSessionFactory();
}

And here is how I'm adding new Foo:

        Foo foo = new Foo { Name = "name1" };
        foo.Children = new List<Bar>();
        foo.Children.Add(new Bar { Description = "desc1" });
        foo.Children.Add(new Bar { Description = "desc2" });

        using (ISession session = NHibirnateHelper.OpenSession())
            using (ITransaction transaction = session.BeginTransaction())
            {
                session.Save(foo);
                transaction.Commit();
            }

When calling Save(foo) method I have an exception "Invalid Cast (check your mapping for property type mismatches); setter of Test.Foo". With iinere exception: ""Unable to cast object type \\"NHibernate.Collection.Generic.PersistentGenericSet 1[Test.Bar]\\" к типу \\"System.Collections.Generic.List 1[Test.Bar]\\"".

What I'm doing wrong?

Answer 1

Try changing public virtual List<Bar> Children { get; set; } public virtual List<Bar> Children { get; set; } public virtual List<Bar> Children { get; set; } to public virtual ISet<Bar> Children { get; set; } public virtual ISet<Bar> Children { get; set; } public virtual ISet<Bar> Children { get; set; } . ISet can be found in Iesi.Collections.Generic.ISet<> .

You could even try using IList instead of List and see if it works.Avoid using concrete classes for the collections and try using interfaces so that Nhibernate could inject its own concrete implementations.