Hello I have this table structure (can't change it)

Table A
ID(Key) RefCode
1 A
2 A
3 B

Table B
RefCode(Key) Value
A 99
A 188
B 300

In want the collection of value from Table B where TableA.RefCode = TableB.RefCode

EntityA.ListeEntityB => EntityA(ID= 1) must return two EntityB ((Value=99);(Value=188)

The problem in this structure is that the relation is non on primary key

So if I write this mapping :

<class name="EntityA" table="TableA">
<id name="Id" column="ID" unsaved-value="0">
<generator class="native" />
</id>

<bag name="ListeEntityB" table="TableB">
<key column="RefCode"></key>
<one-to-many class="EntityB" />
</bag>
</class>

nhibernate does not make the relation
TableA.RefCode = TableB.RefCode But
TableA.ID = TableB.RefCode (because ID is the primary key of Table A)

How can in configure nhibernate to map a collection not from the ID of the source table TableA(ID) but to another column (in my case RefCode) ) ?

Thanks