Nhibernate one-to-many with table per subclass

Question

I am customizing N2CMS's database structure, and met with an issue. The two classes are listed below.

public class Customer : ContentItem
{
  public IList<License> Licenses { get; set; }
}

public class License : ContentItem
{
  public Customer Customer { get; set; }
}

The nhibernate mapping are as follows.

  <class name="N2.ContentItem,N2" table="n2item">
    <cache usage="read-write" />
    <id name="ID" column="ID" type="Int32" unsaved-value="0" access="property">
      <generator class="native" />
    </id>
    <discriminator column="Type" type="String" />
  </class>

  <subclass name="My.Customer,My" extends="N2.ContentItem,N2" discriminator-value="Customer">
    <join table="Customer">
      <key column="ItemID" />
      <bag name="Licenses" generic="true" inverse="true">
        <key column="CustomerID" />
        <one-to-many class="My.License,My"/>
      </bag>
    </join>
  </subclass>

  <subclass name="My.License,My" extends="N2.ContentItem,N2" discriminator-value="License">
    <join table="License" fetch="select">
      <key column="ItemID" />
      <many-to-one name="Customer" column="CustomerID"  class="My.Customer,My" not-null="false" />
    </join>
  </subclass>

Then, when get an instance of Customer, the customer.Licenses is always empty, but actually there are licenses in the database for the customer. When I check the nhibernate log file, I find that the SQL query is like:

SELECT   licenses0_.CustomerID     as CustomerID1_,
         licenses0_.ID             as ID1_,
         licenses0_.ID             as ID2_0_,
         licenses0_1_.CustomerID   as CustomerID7_0_,
FROM     n2item licenses0_
         inner join License licenses0_1_
           on licenses0_.ID = licenses0_1_.ItemID
WHERE    licenses0_.CustomerID = 12 /* @p0 */

It seems that nhibernate believes that the CustomerID is in the 'n2item' table. I don't know why, but to make it work, I think the SQL should be something like this.

SELECT   licenses0_.ID             as ID1_,
         licenses0_.ID             as ID2_0_,
         licenses0_1_.CustomerID   as CustomerID7_0_,
FROM     n2item licenses0_
         inner join License licenses0_1_
           on licenses0_.ID = licenses0_1_.ItemID
WHERE    licenses0_1_.CustomerID = 12 /* @p0 */

Could any one point out what's wrong with my mappings? And how can I get the correct licenses of one customer? Thanks in advance.

Answer 1

I'm not sure whether the SQL is incorrect, because the parent class mapping uses a discriminator so I'd expect all properties to be stored in the same table as the base class (n2item). However I'm not familiar with the "join table" syntax, I generally use joined-subclass so I might be misunderstanding.

Assuming the subclass mapping is correct, could the problem with the licenses be something to do with no Cascade setting being set for that collection?

Answer 2

Hi,

I meet a same problem on my project.

Do you have a solution at your issue?

Thx