Doesn't update many to many attribute using NHibernate - asp.net-mvc-4

Question

Suppose I have only two classes: Group and User. User has groups and Group has members (instance of users)
public class User {
public virtual int id { set; get; }
public virtual string username { set; get; }
public virtual IList<Group> groups { set; get; }
public User()
{
groups = new List<Group>();
}
public virtual void joinGroup(Group group)
{
if (this.groups.Contains(group))
throw new AlreadyJoinedException();
group.members.Add(this);
this.groups.Add(group);
}
public class Group
{
public virtual int id { set; get; }
public virtual string name { set; get; }
public virtual User administrator { set; get; }
public virtual IList<User> members { set; get; }
public Group()
{
members = new List<User>();
}
As you can see the domain it's quite simple. I've already mapped both classes correctly using Fluent NHibernate,
public class UserMapping : ClassMap<User>
{
public UserMapping()
{
this.Id(user => user.id).GeneratedBy.Identity();
this.Map(user => user.username).Not.Nullable().Length(50).Not.LazyLoad();
this.HasManyToMany(user => user.groups).Table("MemberPerGroup").ParentKeyColumn("id_user").ChildKeyColumn("id_group").Not.LazyLoad();
}
}
public class GroupMapping : ClassMap<Group>
{
public GroupMapping()
{
this.Id(group => group.id).GeneratedBy.Identity();
this.Map(group => group.name).Not.Nullable().Length(50).Not.LazyLoad();
this.References(group => group.administrator).Not.Nullable().Not.LazyLoad();
this.HasManyToMany(group => group.members).Table("MemberPerGroup").ParentKeyColumn("id_group").ChildKeyColumn("id_user").Not.LazyLoad();
}
}
I'm progamming a web application using ASP MVC 4. My problem shows up when a user tries to join group. It doesn't break but it neither works fine (doesn't insert into the table the new row in MemberPerGroup). I'm doing something like it:
public void JoinGroup(User user,Group group){
this.userRepository.GetSessionFactory().TransactionalInterceptor(() =>
{
user.joinGroup(group);
});
}
Thanks in advance.
Ivan.

Answer 1

It seems your mapping has no cascading set?
this.HasManyToMany(group => group.members)
.Table("MemberPerGroup")
.ParentKeyColumn("id_group")
.ChildKeyColumn("id_user")
.Not.LazyLoad()
.Cascade.SaveUpdate();
I'm curious - why do you use GetSessionFactory()? our repositories take an ISession object in the constructor, (injected by autofac, but that's irrelevant) from which we start our queries:
// even better to use a transaction, but this is just a sample
_session.SaveOrUpdate(user);
_session.Flush();