Nhibernate: One-To-Many mapping problem - Cannot cascade delete without inverse. Set NULL error

Question

Hi,

I have the current scenario whereby an Article has only 1 Outcome each. Each Article may or may not have an Outcome.

In theory, this is a one-to-one mapping, but since NHibernate does not really support one-to-one, I used a One-To-Many to substitute. My Primary Key on the child table is actually the ArticleID (FK).

So I have the following setup:

Classes

public class Article
{
    public virtual Int32 ID { get;set;}
    private ICollection<ArticleOutcome> _Outcomes {get;set;}

    public virtual ArticleOutcome Outcome
    {
        get {
            if( this._Outcomes !=null && this._Outcomes.Count > 0 )
                return this._Outcomes.First();
            return null;
        }
        set {
            if( value == null ) {
                if( this._Outcomes !=null && this._Outcomes.Count > 0 )
                    this._Outcomes.Clear();
            }
            else {
                if( this._Outcomes == null )
                    this._Outcomes = new HashSet<ArticleOutcome>();
                else if ( this._Outcomes.Count >= 1 )
                    this._Outcomes.Clear();
                this._Outcomes.Add( value );
            }
        }
    }
}

---

public class ArticleOutcome
{
    public virtual Int32 ID { get;set; }
    public virtual Article ParentArticle { get;set;}
}

---

Mappings

public class ArticleMap : ClassMap<Article> 
{
    public ArticleMap() {
        this.Id( x=> x.ID ).GeneratedBy.Identity();

        this.HasMany<ArticleOutcome>( Reveal.Property<Article>("_Outcomes") )
            .AsSet().KeyColumn("ArticleID")
            .Cascade.AllDeleteOrphan() //Cascade.All() doesn't work too.
            .LazyLoad()
            .Fetch.Select();
    }
}

---

public class ArticleOutcomeMap : ClassMap<ArticleOutcome>
{
    public ArticleOutcomeMap(){
       this.Id( x=> x.ID, "ArticleID").GeneratedBy.Foreign("ParentArticle");

       this.HasOne( x=> x.ParentArticle ).Constrained ();

       //This do not work also.
       //this.References( x=> x.ParentArticle, "ArticleID" ).Not.Nullable(); 
    }
}

---

Now my problem is this:

It works when I do an insert/update of the Outcome. e.g.

var article = new Article();
article.Outcome = new ArticleOutcome { xxx = "something" };
session.Save( article );

However, I encounter SQL errors when attempting to delete via the Article itself.

var article = session.Get( 123 );
session.Delete( article ); //throws SQL error.

The error is something to the like of Cannot insert NULL into ArticleID in ArticleOutcome table.

The deletion works if I place Inverse() to the Article's HasMany() mapping, but insertion will fail.

Does anyone have a solution for this? Or do I really have to add a surrogate key to the ArticleOutcome table?

---

Solution

Here's the mapping for Fluent if anyone is interested.

public class ArticleMap : ClassMap<Article> 
{
    public ArticleMap() {
        this.Id( x=> x.ID ).GeneratedBy.Identity();

        this.HasOne( x=> x.Outcome ).Cascade.All();
    }
}


public class Article 
{
    //... other properties

    public virtual ArticleOutcome Outcome { get;set;}
}

Answer 1

NHibernate does support one-to-one.

I have a case very similar to yours. Here are the relevant parts:

class Articule
{
    public virtual ArticleOutcome Outcome { get; set; }
}

class ArticuleOutcome
{
    public virtual Article ParentArticle { get; set; }
}

Mapping (sorry, I don't use Fluent, but it shouldn't be hard to translate):

<class name="Article">
  <id name="ID">
    <generator class="identity"/>
  </id>
  <one-to-one name="Outcome" cascade="all"/>
</class/>
<class name="ArticleOutcome">
  <id name="ID" column="ArticleId">
    <generator class="foreign">
      <param name="property">ParentArticle</param>
    </generator>
  </id>
  <one-to-one name="ParentArticle" constrained="true"/>
</class/>

Usage:

var article = new Article();
article.Outcome = new ArticleOutcome
                  {
                      xxx = "something",
                      ParentArticle = article
                  };
session.Save(article);

Delete should work as you are using it now.