I have 2 classes, NetworkInterface and InterfaceGroupType; the NetworkInterface class contains an instance of the NetworkInterfaceType class. The database tables for each are tblNetworkInterface and tblInterfaceGroupType, respectively. tblNetworkInterface has a foreign key, InterfaceGroupTypeID, to tblInterfaceGroupType. All tables have an integer primary key, ID.

Although it's technically a many to one (NetworkInterface is associated with only one InterfaceGroupType; InterfaceGroupTypecan be associated with many NetworkInterfaces), it doesn't make sense for us to include a collection of NetworkInterface objects in the InterfaceGroupTypeclass.

I'm very new at nHibernate and was wondering how I can best do this. I assume a formula can work but is there a better way?

Hibernate version: It's 1.2.0.GA merged with the NH-466 patch (I built a custom version because I needed the 'join' tag)

Name and version of the database you are using: Microsoft SQL Server 2005; Version: 9.00.1406.00; Product Level: RTM; Edition: Developer Edition


Mapping documents:
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="false">

<class name="Netops.CHNOPS.Domain.NetworkInterface.NetworkIntrface, Netops.CHNOPS.Domain" table="dbo.tblNetworkInterface">

<id type="Int32" column="ID" name="ID" unsaved-value="null">
<generator class="identity"></generator>
</id>

<property name="GroupType" formula="(select IGT.TypeName from ltblInterfaceGroupType IGT where IGT.ID = ???.InterfaceGroupTypeID)"/>

</class>

</hibernate-mapping>

Thanks,
Bill

I think you would still have a <many-to-one> element in your mapping for NetworkInterface. For instance:



What you wouldn't have is a <one-to-many> element in your mapping for InterfaceGroupType, because you don't want the collection of NetworkInterfaces.

rmuti is exactly right. Remember that the terms many-to-one, one-to-many, many-to-many are not NHibernate specific terms. They are used commonly in database modeling. The terms are actually the way they are to help you map your object to the appropriate database schema. You do not have to create a collection of items every time you create a many-to-one association.

There is also a one-to-one association but this is NOT what you want. In that case you could never have two network interfaces with the same type.