JasonDentler.com

Here’s the full write-up on my issue from part 5. Since we’re saying all orphan children should be deleted, it seems logical that our DB schema won’t allow orphaned children, meaning Child.Parent_id should have a NOT NULL constraint. However, when I add this constraint and try to do a cascading orphan delete, NHibernate yells at me because I’ve set the Child.Parent to null / nothing.

If I remove this constraint (not good DB practice in my opinion), we see that the orphan is deleted without ever updating Child.Parent_id to NULL, so it won’t violate any database constraints, as far as I can tell.

Here’s the code in VB:

Imports FluentNHibernate.Mapping
Imports NUnit.Framework

Public Class Parent
    Inherits Entity

    Private m_Children As ICollection(Of Child) = New HashSet(Of Child)

    Public Overridable Property Children() As ICollection(Of Child)
        Get
            Return m_Children
        End Get
        Protected Set(ByVal value As ICollection(Of Child))
            m_Children = value
        End Set
    End Property

End Class

Public Class Child
    Inherits Entity

    Private m_Parent As Parent

    Public Overridable Property Parent() As Parent
        Get
            Return m_Parent
        End Get
        Set(ByVal value As Parent)
            m_Parent = value
        End Set
    End Property

End Class

Public Class ParentMapping
    Inherits ClassMap(Of Parent)
    Public Sub New()
        Id(Function(x As Parent) x.ID).GeneratedBy.GuidComb()
        HasMany(Function(x As Parent) x.Children) _
            .AsSet() _
            .WithForeignKeyConstraintName("ParentChildren") _
            .Cascade.AllDeleteOrphan() _
            .Inverse()

    End Sub
End Class

Public Class ChildMapping
    Inherits ClassMap(Of Child)
    Public Sub New()
        Id(Function(x As Child) x.ID).GeneratedBy.GuidComb()
        References(Function(x As Child) x.Parent) _
            .Cascade.All() _
            .WithForeignKey("ChildParent") _
            .Not.Nullable()

    End Sub
End Class

<TestFixture()> _
Public Class ParentMappingTests
    Inherits BaseFixture

    <Test()> _
    Public Sub CanCascadeSaveFromParentToChild()
        Dim ID As Guid
        Dim P As Parent
        Dim C As Child
        Using Scope As New SQLiteDatabaseScope(Of ParentMapping)
            Using Session = Scope.OpenSession
                Using Tran = Session.BeginTransaction
                    P = New Parent

                    'Add a child of the parent
                    C = New Child With {.Parent = P}
                    P.Children.Add(C)

                    ID = Session.Save(P)
                    Tran.Commit()
                End Using
                Session.Clear()

                Using Tran = Session.BeginTransaction

                    P = Session.Get(Of Parent)(ID)

                    Assert.IsNotNull(P)
                    Assert.AreEqual(ID, P.ID)

                    Assert.AreEqual(1, P.Children.Count)
                    Assert.AreNotSame(C, P.Children(0))
                    Assert.AreEqual(C, P.Children(0))
                    Assert.AreSame(P.Children(0).Parent, P)

                    Tran.Commit()
                End Using

            End Using
        End Using

    End Sub

    <Test()> _
    Public Sub CanDeleteOrphanFromParentToChildren()
        Dim ID As Guid
        Dim P As Parent
        Dim C As Child
        Using Scope As New SQLiteDatabaseScope(Of ParentMapping)
            Using Session = Scope.OpenSession
                Using Tran = Session.BeginTransaction
                    P = New Parent

                    'Add a child of the parent
                    C = New Child With {.Parent = P}
                    P.Children.Add(C)

                    ID = Session.Save(P)
                    Tran.Commit()
                End Using
                Session.Clear()

                Using Tran = Session.BeginTransaction

                    P = Session.Get(Of Parent)(ID)

                    Assert.IsNotNull(P)
                    Assert.AreEqual(ID, P.ID)

                    Assert.AreEqual(1, P.Children.Count)
                    Assert.AreNotSame(C, P.Children(0))
                    Assert.AreEqual(C, P.Children(0))
                    Assert.AreSame(P.Children(0).Parent, P)

                    Tran.Commit()
                End Using
                Session.Clear()

                'Orphan the child
                C = P.Children(0)
                P.Children.Remove(C)
                C.Parent = Nothing

                Using Tran = Session.BeginTransaction
                    'Orhpaned child should be deleted
                    Session.SaveOrUpdate(P)
                    Tran.Commit()
                End Using
                Session.Clear()

                Using Tran = Session.BeginTransaction
                    P = Session.Get(Of Parent)(ID)

                    Assert.AreEqual(0, P.Children.Count)

                    Tran.Commit()
                End Using

            End Using
        End Using
    End Sub

End Class

Here’s the code in C#:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NHibernate;
using FluentNHibernate.Mapping;
using NUnit.Framework;

namespace NStackExample.Data.Tests
{

    public class Parent : Entity
    {

        private ICollection<Child> m_Children = new HashSet<Child>();

        public virtual ICollection<Child> Children
        {
            get { return m_Children; }
            protected set { m_Children = value; }
        }

    }

    public class Child : Entity
    {

        private Parent m_Parent;

        public virtual Parent Parent
        {
            get { return m_Parent; }
            set { m_Parent = value; }
        }

    }

    public class ParentMapping : ClassMap<Parent>
    {
        public ParentMapping()
        {
            Id((Parent x) => x.ID).GeneratedBy.GuidComb();
            HasMany((Parent x) => x.Children)
                .AsSet()
                .WithForeignKeyConstraintName("ParentChildren")
                .Cascade.AllDeleteOrphan()
                .Inverse();
        }
    }

    public class ChildMapping : ClassMap<Child>
    {
        public ChildMapping()
        {
            Id((Child x) => x.ID).GeneratedBy.GuidComb();
            References((Child x) => x.Parent)
                .Cascade.All()
                .WithForeignKey("ChildParent")
                .Not.Nullable();
        }
    }

    [TestFixture()]
    public class ParentMappingTests
    {

        [Test()]
        public void CanCascadeSaveFromParentToChild()
        {
            Guid ID;
            Parent P;
            Child C;
            using (SQLiteDatabaseScope<ParentMapping> Scope = new SQLiteDatabaseScope<ParentMapping>())
            {
                using (ISession Session = Scope.OpenSession())
                {
                    using (ITransaction Tran = Session.BeginTransaction())
                    {
                        P = new Parent();

                        //Add a child of the parent
                        C = new Child { Parent = P };
                        P.Children.Add(C);

                        ID = (Guid) Session.Save(P);
                        Tran.Commit();
                    }
                    Session.Clear();

                    using (ITransaction Tran = Session.BeginTransaction())
                    {

                        P = Session.Get<Parent>(ID);

                        Assert.IsNotNull(P);
                        Assert.AreEqual(ID, P.ID);

                        Assert.AreEqual(1, P.Children.Count);
                        Assert.AreNotSame(C, P.Children.First());
                        Assert.AreEqual(C.ID , P.Children.First().ID );
                        Assert.AreSame(P.Children.First().Parent, P);

                        Tran.Commit();

                    }
                }

            }
        }

        [Test()]
        public void CanDeleteOrphanFromParentToChildren()
        {
            Guid ID;
            Parent P;
            Child C;
            using (SQLiteDatabaseScope<ParentMapping> Scope = new SQLiteDatabaseScope<ParentMapping>())
            {
                using (ISession Session = Scope.OpenSession())
                {
                    using (ITransaction Tran = Session.BeginTransaction())
                    {
                        P = new Parent();

                        //Add a child of the parent
                        C = new Child { Parent = P };
                        P.Children.Add(C);

                        ID = (Guid) Session.Save(P);
                        Tran.Commit();
                    }
                    Session.Clear();

                    using (ITransaction Tran = Session.BeginTransaction())
                    {

                        P = Session.Get<Parent>(ID);

                        Assert.IsNotNull(P);
                        Assert.AreEqual(ID, P.ID);

                        Assert.AreEqual(1, P.Children.Count);
                        Assert.AreNotSame(C, P.Children.First());
                        Assert.AreEqual(C.ID, P.Children.First().ID );
                        Assert.AreSame(P.Children.First().Parent, P);

                        Tran.Commit();
                    }
                    Session.Clear();

                    //Orphan the child
                    C = P.Children.First();
                    P.Children.Remove(C);
                    C.Parent = null;

                    using (ITransaction Tran = Session.BeginTransaction())
                    {
                        //Orhpaned child should be deleted
                        Session.SaveOrUpdate(P);
                        Tran.Commit();
                    }
                    Session.Clear();

                    using (ITransaction Tran = Session.BeginTransaction())
                    {
                        P = Session.Get<Parent>(ID);

                        Assert.AreEqual(0, P.Children.Count);

                        Tran.Commit();

                    }
                }
            }
        }

    }


}