NHibernate Many-to-one cascade - nhibernate

Question

I have the below two classes:
public class Project
{
public virtual int ProjectId { get; set; }
public virtual string ProjectName { get; set; }
public virtual LegalEntity LegalEntity { get; set; }
}
and
public class LegalEntity
{
public virtual int LegalEntId { get; set; }
public virtual string Name { get; set; }
}
with mappings as:
<class name="Project" table="Project" dynamic-update="true">
<id name="ProjectId">
<generator class="native"/>
</id>
<property name="ProjectName" />
<many-to-one name="LegalEntity" column="LegalEntId" fetch="join" cascade="all-delete-orphan" />
</class>
and
<class name="LegalEntity" table="LegalEnt" dynamic-update="true">
<id name="LegalEntId">
<generator class="native"/>
</id>
<property name="Name" />
</class>
In database, Project table has a FK to LegalEntity's PK column. One Project will have only one legal entity. Different projects can have same legal entity. So thats the reason I have gone for many-to-one. Not sure if this is correct though.
Insert and update is working fine. But if I update a legal entity id in a project and that legal entity becomes orphan, I want it to be deleted. But its not happening. Am I wrong in understanding delete-all-orphan? If yes, how can I achieve this behaviour?

Answer 1

The many-to-one cascade does not support all-delete-orphan, see:
5.1.10. many-to-one
<many-to-one
...
cascade="all|none|save-update|delete" (4)
...
Also, it would be almost impossible to handle this feature by NHibernate's session. Because it does not have to be clear, that the referenced many-to-one is really orphan. There should be some farther checks in DB... there could be other places referencing this table row...
Suggestion: do it in your code as a part of the DAO or Business Facade implementation. Check if there are really no dependencies, and then issue explicit Delete()
EXTEND: Here is a QueryOver syntax to get a list of all "orphan" LegalEntity
// subquery
var subquery = QueryOver.Of<Project>()
.Select(x => x.LegalEntity.LegalEntId);
// just these legal entities, which are NOT used
var query = session.QueryOver<LegalEntity>()
.WithSubquery
.WhereProperty(y => y.LegalEntId)
.NotIn(subquery)
;
// orphans
var list = query
.List<LegalEntity>();

Answer 2

Now all-delete-orphan and delete-orphan have been implemented for many-to-one as you can see in this commit from Nov 19, 2014.
Those were not supported when the OP asked the questions or when Radim Köhler wrote his answer, but I think future visitors will appretiate the update.
The documentation is also updated and now says:
cascade="all|none|save-update|delete|delete-orphan|all-delete-orphan"
But the documentation is confusing now, because it still has the following note:
The cascade attribute permits the following values: all, save-update, delete, none.
So I've created a defect to fix that last part of the documentation.