Question

I am having a problem trying to map out a many-to-many relationship , where both sides of the relationship reference the same entity. I am using Fluent NHibernate and NH3.1.

Basically, the scenario is this – I have a category, which can have multiple parents. Thus, a category has multiple other categories as parents, as well as multiple other categories as its children.

HasManyToMany(x => x.ParentCategories).AsBag().Table("parentcategorychildren").ParentKeyColumn("ChildID").ChildKeyColumn("ParentID").Cascade.SaveUpdate();
HasManyToMany(x => x.ChildrenCategories).AsBag().Table("parentcategorychildren").ParentKeyColumn("ParentID").ChildKeyColumn("ChildID").Inverse();

However, when I try to build the factory, I get the following error:

The relationship Category.ChildrenCategories to Category.ChildrenCategories has Inverse specified on both sides. Remove Inverse from one side of the relationship.

What I am finding strange is why is it mentioning ‘Category.ChildrenCategories’ to Category.ChildrenCategories, as opposed to ParentCategories?

Any help would be greatly appreciated !

I just created a bounty for this, because it’s important enough to me. Please, I’m not interested in “you can’t do this” as an answer.

Answer 1

This is most likely a FNH bug and it is most likely already fixed in the latest FNH source code. There is no problem when using FNH1.0 and NH2.1. Equivalent HBM mapping works well in FNH1.2 and NH3.1:

<bag name="ParentCategories" cascade="all" table="parentcategorychildren">
    <key column="ChildID" />
    <many-to-many column="ParentID" class="Category" />
</bag>

<bag name="ChildrenCategories" inverse="true" table="parentcategorychildren">
    <key column="ParentID" />
    <many-to-many column="ChildID" class="Category" />
</bag>

EDIT:
After digging in FNH source code I found a workaround. Let’s say, your configuration looks like this:

.Mappings(m => {
    m.FluentMappings.AddFromAssemblyOf<Category>();
})

The unlucky code can be suppressed by this configuration:

.Mappings(m => {
    var persistenceModel = new PersistenceModel();
    persistenceModel.AddMappingsFromAssembly(typeof(Category).Assembly);
    persistenceModel.ValidationEnabled = false; // this makes the trick
    m.UsePersistenceModel(persistenceModel);
})