NHibernate custom collection type

Question

I'm having an entity object called Patient and this entity is having a property called Visits which is of type VisitsCollection .

VisitsCollections is a child class of IList<Visit> but it also adds some custom logic to the collection (like auto ordering, some validation, notifications, etc..).

I need to use the custom collection type as it adds some data to the entities that are added to the collection and performs some other paperwork transparently.

Now I want to map that in NHibernate, so I've created:

<list name="Visits" lazy="true" fetch="select">
    <key foreign-key="PatientId" />
    <index column="Timestamp" />
    <one-to-many class="Visit" not-found="ignore"/>
</list>

I'm getting an exception:

Unable to cast object of type 'NHibernate.Collection.PersistentList' to type '...VisitsCollection'

Whenever I'm accessing the visits property.

I've also tried to map it this way:

<list name="Visits" lazy="true" fetch="select" collection-type="VisitsCollection">
    <key foreign-key="PatientId" />
    <index column="Timestamp" />
    <one-to-many class="Visit" not-found="ignore"/>
</list>

but still, I'm getting this exception:

Custom type does not implement UserCollectionType: .....VisitsCollection

I don't want to inherit my VisitsCollection from any NHibernate type as the collection class is part of a framework that I want it to be DAL-agnostic (as it will be used in many scenarios - not only with a database).

Any ideas on how to map this, preserving the structure of my code?

Thanks in advance.

Answer 1

I never use custom collection types, mainly because I'm lazy. NHibernate wants you to use a IUserCollectionType I believe, which requires a bit of plumbing.

Rather than that, my first stop would be to look at using extension methods as discussed by Billly McCafferty . But you have code written so...

Alternatively, you could map your collection as a component as discussed here by Colin Jack . This might be easier for your scenario?

Also check this SO thread .

Answer 2

I also vote up not to use custom collections. Anyway, you can do it via component.

<component name="Warehouses" class="Core.Domain.Collections.EntitySet`1[Core.Domain.OrgStructure.IWarehouseEntity,Core],Core">
<set name="_internalCollection" table="`WAREHOUSE`" cascade="save-update" access="field" generic="true" lazy="true" >
  <key column="`WarehouseOrgId`" foreign-key="FK_OrgWarehouse" />
  <!--This is used to set the type of the collection items-->
  <one-to-many class="Domain.Model.OrgStructure.WarehouseEntity,Domain"/>
</set>

How to map NHibernate custom collection with fluentNHibernate?

Answer 3

Just for reference, here is how you could do it using FluentNHibernate

Whether we should or should not create a custom collection type is a separate topic IMHO

public class PatientOverride : IAutoMappingOverride<Patient>
{
        public void Override(AutoMapping<Patient> mapping)
        {
             mapping.Component(
                x => x.Visits,
                part =>
                {
                    part.HasMany(Reveal.Member<VisitsCollection, IEnumerable<Visit>>("backingFieldName")) // this is the backing field name for collection inside the VisitsCollection class
                    .KeyColumn("PatientId")
                    .Inverse(); // depends on your use case whether you need it or not
                });
        }
}