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

问题

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!

回答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>

回答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.

来源：https://stackoverflow.com/questions/1638593/unable-to-cast-object-of-type-nhibernate-collection-generic-persistentgenericbag