NHibvernate 3.2 many to many not populating join table

Question

I have two classes, user and role, defined as:

public class User : Entity
{
    // other properties ...
    public virtual string Username
    public virtual ICollection<Role> Roles { get; set; }
}

public class Role : Entity
{
    public virtual string Name { get; set; }
    public virtual ICollection<User> Users { get; set; }
}

In my mapping code, I have the following:

mapper.Class<User>(map =>
{
    map.Bag(x=>x.Roles,
        cm=>
        {
            cm.Table("UserRole");
            cm.Cascade(Cascade.All);
            cm.Key(k => k.Column("[User]"));
        },
        em=>
        {
            em.ManyToMany(mm =>
            {
                mm.Column("[Role]");
            });
        });

});

mapper.Class<Role>(map =>
{
    map.Bag(x=>x.Users, 
        cm=>
        {
            cm.Inverse(true);
            cm.Table("UserRole");                        
            cm.Key(k=>k.Column("[Role]"));
        },
        em =>
        {
            em.ManyToMany(mm =>
            {
                mm.Column("[User]");
            });
        });
});

The mappings generate the expected schema, but the join table is never populated. Adding a new user with a new Role in its collection persists the role and then the user to the appropriate tables, but the join table is left empty. Why?

Edit: I still have not made any progress on this. I'm absolutely sure the mapping is correct, and the correct schema is generated, but the join table simply isn't populated. For test purposes, I'm generating entities using NBuilder like so:

var roles = new Role[] 
{
    new Role("Admin"),
    new Role("Manager"),
    new Role("User")
};

var users = Builder<User>.CreateListOfSize(10)
    .TheFirst(1)
        .Do(x =>
            {
                x.Roles.Add(roles[0]);
                x.Roles.Add(roles[1]);
                roles[0].Users.Add(x);
                roles[1].Users.Add(x);
            })
    .All()
        .With(x => x.Id = 0)
        .And(x => x.Version = 0)
        .And(x => x.Username = "test user")
        .And(x => x.Password = "test password")
        .Do(x => 
        {
            x.Roles.Add(roles[2]);
            roles[2].Users.Add(x);
        }
    .Build();


foreach (var u in users) session.Save(u);

The User and Role entities are persisted correctly, but the join table remains empty. This means I cannot effective query the roles for a given user later, which nullifies the point.

score 1 · Answer 1 · edited May 23 '17 at 12:27

Make sure you have both classes referencing each other.

I think that code, similar to one below, should work for you:

role.Users.Add(user);    
user.Roles.Add(role);

session.Save(user); // NH only saves user and role, so it can get auto-generated identity fields
session.Flush(); // NH now can save into cross-ref table, because it knows required information (Flush is also called inside of Transaction.Commit())

I found a good answer to a question about many-to-many with lot of explanations and quotes from NH documentation. I think it worth to read it.

[EDIT]

In answer to this somewhat similar question there is discussion in which need for explicit transaction to save into cross-table is mentioned.

I also edited code above with adding session.Flush() to reflect my findings.

score 0 · Accepted Answer · answered Apr 01 '12 at 17:16

0

I ended up downloading the NHibernate source and referencing that directly so I could step through it. It turns out that it had something to do with the fact that my code for generating the test data was not wrapped in an explicit session transaction. Once I added that, it was fine. I'd love to see some kind of explanation on this, as I wasn't able to follow the code very clearly, but I'm at least satisfied that the problem is solved.

answered Apr 01 '12 at 17:16

Chris

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Great that you figured that out! – Andriy Buday Apr 01 '12 at 17:21
Also I think that session.Flush(); after saving should also work (without explicit transaction). User and Role are saved without need for transaction, because NH needs to get feedback from database (like auto-generated ids) after that NH can save records to cross-table. – Andriy Buday Apr 01 '12 at 17:33
Don't try to work around this behavior by using flush. nhibernate is designed to use explicit transctions, so you want to embrace that. See e.g. the NHProf documentation: http://nhprof.com/Learn/Alerts/DoNotUseImplicitTransactions – Jonas Høgh Apr 01 '12 at 18:27
I don't argue with this, I just wanted to highlight where actual insert into cross-table happens. – Andriy Buday Apr 01 '12 at 19:44

NHibvernate 3.2 many to many not populating join table

2 Answers2