NHibernate Many-to-one cascade

Question

I have the below two classes:

public class Project
{

    public virtual int ProjectId { get; set; }
    public virtual string ProjectName { get; set; }
             


        

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.}}