Many to many relationship using Fluent Nhibernate Automapping

Question

We are facing problem applying many-to-many relationship using fluent nhibernate automapping.

The simplified form of domain model are as follows:

public class Group
{
    private readonly IList<Recipient> _recipients = new List<Recipient>();
    public virtual IList<Recipient> Recipients
    {
        get { return _recipients; }
    }
}

public class Recipient
{
    private readonly IList<Group> _groups = new List<Group>();
    public virtual IList<Group> Groups
    {
        get { return _ groups; }
    }
}

As the code above describes that Group and Recipient are having many-to-many relationship. We are using automapping feature of fluent nhibernate to map our domain model with database. So, we needed to use Convention for automapping. Following is code we used for many to many convention:-

public class ManyToManyConvention : IHasManyToManyConvention
{
    #region IConvention<IManyToManyCollectionInspector,IManyToManyCollectionInstance> Members

    public void Apply(FluentNHibernate.Conventions.Instances.IManyToManyCollectionInstance instance)
    {
        if (instance.OtherSide == null)
        {
            instance.Table(
               string.Format(
                   "{0}To{1}",
                   instance.EntityType.Name + "_Id",
                   instance.ChildType.Name + "_Id"));
        }
        else
        {
            instance.Inverse();
        }
        instance.Cascade.All();
    }

    #endregion
}

I found this solution here :

http://blog.vuscode.com/malovicn/archive/2009/11/04/fluent-nhibernate-samples-auto-mapping-part-12.aspx#Many%20to%20Many%20convention

But in above code while debugging both time for Recipients-> Groups and for Groups->Recipients instance.OtherSide is coming not null. The assumption was 1st time instance.OtherSide will be not null and second time it will be null as relationship is applied on one side so we will just apply inverse to that. So it’s creating 2 mapping tables which are same. It is load to database to have 2 tables of same schema. Even when I try to save our domain model to database using many to many relationship. It’s saving only 1 side i.e it saves Recipients in the Groups , But not saving Groups in Recipients.In database also it is having entry in only one mapping table not in both.

So , the question is Are we doing the right thing? If not then how to do it.

Firo Firo · Accepted Answer · 2012-02-17T10:16:36

you could take inverse itself as a criteria

    public void Apply(IManyToManyCollectionInstance instance)
    {
        Debug.Assert(instance.OtherSide != null);
        // Hack:  the cast is nessesary because the compiler tries to take the Method and not the property
        if (((IManyToManyCollectionInspector)instance.OtherSide).Inverse)
        {
            instance.Table(
               string.Format(
                   "{0}To{1}",
                   instance.EntityType.Name + "_Id",
                   instance.ChildType.Name + "_Id"));
        }
        else
        {
            instance.Inverse();
        }
        instance.Cascade.All();
    }

Many to many relationship using Fluent Nhibernate Automapping

1 Answers