Fluent NHibernate Many-to-Many

Question

I am using Fluent NHibernate and having some issues getting a many to many relationship setup with one of my classes. It's probably a stupid mistake but I've been stuck for a little bit trying to get it working. Anyways, I have a couple classes that have Many-Many relationships.

public class Person
{
    public Person()
    {
        GroupsOwned = new List<Groups>();
    }

    public virtual IList<Groups> GroupsOwned { get; set; }
}

public class Groups
{
    public Groups()
    {
        Admins= new List<Person>();
    }

    public virtual IList<Person> Admins{ get; set; }
}

With the mapping looking like this

Person: ...

HasManyToMany<Groups>(x => x.GroupsOwned)
    .WithTableName("GroupAdministrators")
    .WithParentKeyColumn("PersonID")
    .WithChildKeyColumn("GroupID")
    .Cascade.SaveUpdate();

Groups: ...

 HasManyToMany<Person>(x => x.Admins)
    .WithTableName("GroupAdministrators")
    .WithParentKeyColumn("GroupID")
    .WithChildKeyColumn("PersonID")
    .Cascade.SaveUpdate();

When I run my integration test, basically I'm creating a new person and group. Adding the Group to the Person.GroupsOwned. If I get the Person Object back from the repository, the GroupsOwned is equal to the initial group, however, when I get the group back if I check count on Group.Admins, the count is 0. The Join table has the GroupID and the PersonID saved in it.

Thanks for any advice you may have.

Answer 1

Are you making sure to add the Person to the Groups.Admin? You have to make both links.

Answer 2

@emeryc; Thanks -- I did that and when I do, it adds two identical records to the Join table. My tests pass but why would it add two refs like that?

Answer 3

You have three tables right?

People, Groups, and GroupAdministrators

when you add to both sides you get

People (with an id of p1) Groups (with an id of g1)

and in GroupAdministrators you have two columns and a table that has

(p1,g1)

(p1,g1)

and your unit test code looks like the following.

Context hibContext //Built here
Transaction hibTrans //build and start the transaction.

Person p1 = new Person()
Groups g1 = new Groups()

p1.getGroupsOwned().add(g1)
g1.getAdmins().add(p1)

hibTrans.commit();
hibContext.close();

And then in your test you make a new context, and test to see what's in the context, and you get back the right thing, but your tables are all mucked up?

Answer 4

The fact that it is adding two records to the table looks like you are missing an inverse attribute. Since both the person and the group are being changed, NHibernate is persisting the relation twice (once for each object). The inverse attribute is specifically for avoiding this.

I'm not sure about how to add it in mapping in code, but the link shows how to do it in XML.

Answer 5

@Santiago I think your right.

The answer might just be that you need to remove one of your ManyToMany declarations, looking more at Fluent it looks like it might be smart enough to just do it for you.