How-to: Mapping (NHibernate) multiple classes with

I am currently working with a brownfield database which contains a table which holds data for 3 different sorts of business. It has to do with SalesOrders and orderlines. In the old application, we were able to add 3 types of orderlines to each salesorder: products, hourly rates and text lines. 15 years ago, this was a quick and dirty solution to get easy queries in Delphi to get all the lines in one datagrid. Every

Now I am trying to build the object model in C# using NHibernate. I've made 3 seperate entities without a base class, due to the fact that these 3 line types have no real business logical connection. However, I want to get these 3 types into one list so I can order them.

I've considered using inheritence, table per class, as the table meets the requirements (no columns with a not-null restraint). This isn't a logical step though, since the business per type is completely different (only things in common are userId, description and remarks). Perhaps a component? but how to map the properties to 3 different classes without a base class or any kind of link except the table name?

I hope you guys understood what I wrote. I have no real code yet, I was just sketching some stuff on paper on how to deal with this code.

Anyone here who can help me on my way?

Kind regards, Ted

You could put an interface on the three entities and map it as a base class, all to the same table:

interface IWhatever 
{
  // central Id for the whole table
  int Id { get; set; }
  // may be some more properties
}

class Product : IWhatever
{
  // ...
}

class HourlyRate : IWhatever
{
  // ...
}

class TextLines : IWhatever
{
  // ...
}

Mapping:

<class name="IWhatever" table="MyBigTable">

  <id .../>
  <discriminator column="Type"/>
  <subclass name="Product" discriminator-value="P">
    <!-- ... -->
  </subclass>
  <subclass name="HourlyRate" discriminator-value="HR">
    <!-- ... -->
  </subclass>
  <subclass name="TextLines" discriminator-value="TL">
    <!-- ... -->
  </subclass>
</class>