Unable to cast object of type NHibernate.Collection.Generic.PersistentGenericBag to List

Question

I have a class called ReportRequest as:

public class ReportRequest
{
    Int32 templateId;
    List<Int32> entityIds;

    public virtual Int32? Id
    {
        get;
        set;
    }

    public virtual Int32 TemplateId
    {
        get { return templateId; }
        set { templateId = value; }
    }

    public virtual List<Int32> EntityIds
    {
        get { return entityIds; }
        set { entityIds = value; }
    }

    public ReportRequest(int templateId, List<Int32> entityIds)
    {
        this.TemplateId = templateId;
        this.EntityIds = entityIds;
    }
}

It is mapped using Fluent Hibernate as:

public class ReportRequestMap : ClassMap<ReportRequest>
{
    public ReportRequestMap()
    {
        Id(x => x.Id).UnsavedValue(null).GeneratedBy.Native();
        Map(x => x.TemplateId).Not.Nullable();            
        HasMany(x => x.EntityIds).Table("ReportEntities").KeyColumn("ReportRequestId").Element("EntityId").AsBag().Cascade.AllDeleteOrphan();
    }
}

Now, I create an object of this class as

ReportRequest objReportRequest = new ReportRequest(2, new List<int>() { 11, 12, 15 });

and try to Save the object in database using

session.Save(objReportRequest);

I get the following error: "Unable to cast object of type 'NHibernate.Collection.Generic.PersistentGenericBag1[System.Int32]' to type 'System.Collections.Generic.List1[System.Int32]'."

I am not sure if I have mapped the property EntityIds correctly. Please guide.

Thank you!

Monomial

are you sure you want a list of ints and not a list of related entities? – Joel

Answer 1

Use collection interfaces instead of concrete collections, so NHibernate can inject it with its own collection implementation.

In this case, use IList<int> instead of List<int>

Joel

Thank you! solved the issue. Can you please elaborate a little when you say 'NHibernate can inject it with its own collection implementation.' – Monomial

It's explained here: surcombe.com/nhibernate-1.2/api/html/… – Joel

This link no longer exists. An updated one or the brief content would be much appreciated. – Upbeat

@Noich: elliottjorgensen.com/nhibernate-api-ref/NHibernate.Collection/… – Joel

I am confused by the number of people on stackoverflow complaining about dead links. Has nobody heard of archive.org? web.archive.org/web/20091105034326/http://elliottjorgensen.com/… – Joel

Answer 2

I found that using ICollection<T> worked where IList<T> did not.

I'm no NHibernate wizard, but I did want to throw a bone to someone else who might land on this issue.

Despair

It depends on how your collection is mapped. For bag you can use IList<T> and for set - ISet<T> – Fop