NHibernate Many To Many Relationship - Issue when deleting a part of the relationship

Question

I have a many to many relationship between a Team and an Employee entity.

I mapped them as following:

public class EmployeeMap : ClassMap<Employee>
{
    public EmployeeMap()
    {
        // identifier mapping
        Id(p => p.Id).Column("EmployeeID");

        // column mapping
        Map(p => p.EMail);
        Map(p => p.LastName);
        Map(p => p.FirstName);

        // relationship mapping
        HasManyToMany(m => m.Teams).Table("EmployeeTeam")
            .Inverse()
            .Cascade.All()
            .AsSet()
            .LazyLoad()
            .ParentKeyColumn("EmployeeID")
            .ChildKeyColumn("TeamID");

        HasMany(p => p.LoanedItems).Cascade.SaveUpdate().KeyColumn("EmployeeId");
    }
}

public class TeamMap : ClassMap<Team>
{
    public TeamMap()
    {
        // identity mapping
        Id(p => p.Id).Column("TeamID");

        // column mapping
        Map(p => p.Name);

        // relationship mapping
        HasManyToMany(m => m.Employees)
            .Table("EmployeeTeam")
            .LazyLoad()
            .Cascade.All()
            .AsSet()
            .ParentKeyColumn("TeamID")
            .ChildKeyColumn("EmployeeID");
    }
}

Then I created 3 Teams and 2 Employees:

TeamID  EmployeeID
1       1
1       2
2       2
3       1

The Employee1 has also 2 LoanedItems(Books, Magazines). Employee2 has no LoanedItems.

Now I want to delete Employee1, who is in Team1 and Team3. In Team 1 is also Employee2. So when I delete Employee1, I assume that Employee1 is deleted and also Team3, because I also assume that an Team can only exist when it has an Employe and vice versa. So Team1 may not be deleted, because it has Employee2 and can still exists.

I used the following code lines with a new Session:

var loadedEmployee = session.Get<Employee>(1);
session.Delete(loadedEmployee);
transaction.Commit();

But what happens? -> NHibernate deletes all Teams and all Employees! -> NHibernate updated my LoanedItem table correctly by setting the FK EmployeeID to NULL.

What is wrong there?

Answer 1

Hi! Because of the Cascade.All on the HasManyToMany mapping.

Use Cascade.SaveAndUpdate instead, if you wish to avoid the delete cascade action.

Answer 2

I have answered a similar question here: http://stackoverflow.com/questions/1695063/what-is-the-correct-way-to-define-many-to-many-relationships-in-nhibernate-to-all/

Reading the question and my answer maybe will help you understand what is going on with your many-to-many association.