Cascade issue when deleting an entity in a one-to-one relationship using Fluent NHibernate.

Question

I have the following db tables which I have simplified for this example:

Webpage Id, URLIdentifier

WebpageMetaData Webpage_id Keywords

Webpage_id is the primary key for the table and a foriegn key back to the webpage table.

I am then using Fluent NHibernate and its automapping feature to map these to the following POCO classes:

public class Webpage
{
    public virtual int Id { get; set; }
    public virtual string UrlIdentifier { get; set; }
    public virtual WebpageMetaData WebpageMetaData { get; set; }

}

public class WebpageMetaData
{
    public virtual int Id { get; set; }
    public virtual string Keywords{ get; set; }
    public virtual Webpage Webpage { get; set; }

}

I want to map these entities as one-to-one, so I override the automapping as follows:

public class WebpageMap : IAutoMappingOverride<Webpage>
{        
    public void Override(AutoMapping<Webpage> mapping)
    {
        mapping.HasOne(w => w.WebpageMetaData)
            .Not.Constrained()
            .Fetch.Join()
            .Cascade.All();
    }
}

public class WebpageMetaDataMap : IAutoMappingOverride<WebpageMetaData>
{
    public void Override(AutoMapping<WebpageMetaData> mapping)
    {
        mapping.Id(w => w.Id, "Webpage_id").GeneratedBy.Foreign("Webpage");

        mapping.HasOne(w => w.Webpage)
            .ForeignKey("Webpage_id")
            .Constrained()
            .Fetch.Join()
            .Cascade.None();
    }
}

I have tested these mappings and cascade rules and they work for selecting, inserting and updating. However when i perform a delete of the WebpageMetaData I get an exception saying that

"deleted object would be re-saved by cascade (remove deleted object from associations)[WebpageMetaData#524]"

The only way to stop the exception is by doing the following before saving:

webpageMetaData.Webpage.WebpageMetaData = null;

So I have to set a null reference to myself from my parent??! This seems wrong? have I got my mapping wrong?

Thanks.

Update 1: Please see the NH mappings that FLuent is producing, in case this is of help to the hard core NHibernator's :)

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true">
  <class xmlns="urn:nhibernate-mapping-2.2" name="EveryPage.Core.Domain.Webpage, EveryPage.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="`Webpage`">
    <id name="Id" type="System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" unsaved-value="0">
      <column name="Id" />
      <generator class="identity" />
    </id>
    <one-to-one cascade="all" class="EveryPage.Core.Domain.WebpageMetaData, EveryPage.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" constrained="false" fetch="join" name="WebpageMetaData" />
    <property name="UrlIdentifier" type="System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <column name="UrlIdentifier" />
    </property>    
  </class>
</hibernate-mapping>


<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true">
  <class xmlns="urn:nhibernate-mapping-2.2" name="EveryPage.Core.Domain.WebpageMetaData, EveryPage.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="`WebpageMetaData`">
    <id name="Id" type="System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" unsaved-value="0">
      <column name="Webpage_id" />
      <generator class="foreign">
        <param name="property">Webpage</param>
      </generator>
    </id>
    <one-to-one cascade="none" class="EveryPage.Core.Domain.Webpage, EveryPage.Core, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" constrained="true" fetch="join" foreign-key="Webpage_id" name="Webpage" />
    <property name="Keywords" type="System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <column name="Keywords" />
    </property>
  </class>
</hibernate-mapping>

Answer 1

I think your mapping isn't quite right. If you take a look at the NH documentation, their example of using one-to-one for a parent-child relationship involves a many-to-one mapping (with unique=true) and a one-to-one mapping, not a pair of one-to-one mappings. (A pair of one-to-one mappings is for the case where two tables are associated using a shared PK)

I suggest you try changing your mapping to better match the example to see if that fixes the cascades.

Answer 2

Hm, Cascade-all-delete-orphan maybe?