How configure NHibernate to map to an array if there is no index in the table?

Question

I have an existing POCO class library where children collections are all stored in arrays. For instance, the Customer class has a Invoice[] array to hold its invoices:

class Customer
{
    public int ID;
    public Invoice[] _invoices;
}

class Invoice
{
    public int ID;
    public int CustomerID;
    public string SomeData;
}

I cannot change those classes and I want to map them to an existing database using NHibernate.

I looked at the <array> mapping but it seem to require an <index> element. In my database, the [Invoice] table does not have an index column. When Invoices of a Customer are loaded, I don't expect them to be at any specific position in the array.

What are my options?

Answer 1

Unfortunately, your options are to change either your class or your table.

A) You can change Customer to declare invoices as IList instead of array; you will then be able to map them as unsorted bag. You can even make it sorted by some column:

<bag name="Invoices" table="Invoices" order-by="ID ASC"> <!-- order-by is optional -->
  <key column="CustomerID"/>
  <element column="SomeData" type="String"/>
  <!-- or use one-to-many if Invoice is mapped as entity -->
  <one-to-many class="Whatever.Invoice, Whatever"/>
</bag>

B). You can change your table to contain an index column and map your invoices as real <array>:

<array name="Invoices" table="Invoices" order-by="ID ASC"> <!-- order-by is optional -->
  <key column="CustomerID"/>
  <index column="IndexNr"/>
  <element column="SomeData" type="String"/>
</array>