Question

I think this should be straightforward, but with NHibernate simple things are always the most complicated.

I have two POCOs which reference each other through HasManyToMany:

public class Foo1
{
//other properties
public virtual IList<Foo2> Foo2s {get;set;}
}
public class Foo2
{
//other properties
public virtual IList<Foo1> Foo1s {get;set;}
}

And the mappings:

class Foo1Map : ClassMap<Foo1>
{
//other mappings
HasManyToMany(c => c.Foo2s);
}
class Foo2Map : ClassMap<Foo2>
{
//other mappings
HasManyToMany(c => c.Foo1s);
}

The join table is correctly created, it has 2 fields which are on foreign keys to the respective tables, all fine, the HUGE problem is that those 2 fields should be primary key (or at least unique) while they aren’t. I tried playing around with various fluent methods chained to HasManyToMany but without any result.

How do I get the generated manytomany table to have primary key on the 2 foreign key fields without having to create a custom POCO and map it with composite key?

Thanks.

Answer 1

a unique constraint and also index

class Foo1Map : ClassMap<Foo1>
{
    //other mappings
    HasManyToMany(c => c.Foo2s)
        .ParentKeyColumns.Add("foo1_id", p => p.UniqueKey("unique_constraint1").Index("someIndex"))
        .ChildKeyColumns.Add("foo2_id", p => p.UniqueKey("unique_constraint1"));
}

Updated: or as a convention for HasMany (code like this i used in a project), not nice but working

public class IndexOneToManyColumnsConvention : IHasManyConvention
{
    public void Apply(IOneToManyCollectionInstance instance)
    {
        var mappingfield = instance.Key.Columns.First().GetType()
            .GetField("mapping", BindingFlags.Instance | BindingFlags.NonPublic);

        var columnMapping = (ColumnMapping)mappingfield.GetValue(instance.Key.Columns.First());

        if (!columnMapping.HasValue(c => c.Index))
        {
            var typename = instance.Member.DeclaringType.Name;

            columnMapping.Index = string.Format("index_{0}_{1}",
                typename.ToLower(), instance.Member.Name.ToLower());
        }
    }
}

i think there is the code in the trunk of FNH to get rid of this hack