Question

I have this:

namespace Demo.Framework.Domain
{
    public class UserEntity
    {
        public virtual Guid UserId { get; protected set; }
    }
}

namespace TDemo.Framework.Domain
{
    public class Users : UserEntity
    {
        public virtual string OpenIdIdentifier { get; set; }
        public virtual string Email { get; set; }
        public virtual IList<Movie> Movies { get; set; }
    }
}

namespace Demo.Framework.Domain
{
    public class Movie
    {
        public virtual int MovieId { get; set; }
        public virtual Guid UserId { get; set; } // not sure if I should inherit UserEntity
        public virtual string Title { get; set; }
        public virtual DateTime ReleaseDate { get; set; } // in my ms sql 2008 database I want this to be just a Date type. Not sure how to do that.
        public virtual int Upc { get; set; }

    }
}

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    assembly="Demo.Framework"
    namespace="Demo.Framework.Domain">
    <class name="Users">
        <id name="UserId">
            <generator class="guid.comb" />
        </id>
        <property name="OpenIdIdentifier" not-null="true"  />
        <property name="Email" not-null="true" />      
    </class>
    <subclass name="Movie">
        <list name="Movies" cascade="all-delete-orphan">
            <key column="MovieId" />
            <index column="MovieIndex" /> // not sure what index column is really.
            <one-to-many class="Movie"/>
        </list>
    </subclass>     
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    assembly="Demo.Framework"
    namespace="Demo.Framework.Domain">
    <class name="Movie">      
        <id name="MovieId">
            <generator class="native" />
        </id>
        <property name="Title" not-null="true" />
        <property name="ReleaseDate" not-null="true" type="Date" />
        <property name="Upc" not-null="true" />
        <property name="UserId" not-null="true" type="Guid"/>
    </class>
</hibernate-mapping>

I get this error:

'extends' attribute is not found or is empty.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: NHibernate.MappingException: 'extends' attribute is not found or is empty.

Source Error:

Line 19:             var nhConfig = new Configuration().Configure();
Line 20:             var sessionFactory = nhConfig.BuildSessionFactory();

Answer 1

NHibernate has it’s roots in java, where a subclass “extends” a base class, and this is sometimes a useful mapping element when defining hierachies across different hbm files.

The reason you are seeing that error is the way you are mapping the user’s movies as a “subclass”. This is confusing NHib, since you aren’t extending anything. Remove the “subclass” node surrounding your list and that error will go away.

As an aside, Jamie is right as to why the list index is required. The list mapping is fine, but unless there is a compelling reason to not do so, I typically want set semantics for my one to many relationships, which looks like the example below in an hbm.

HTH,
Berryl

<set access="field.camelcase-underscore" cascade="none" inverse="true" name="Employees">
  <key foreign-key="Employee_Department_FK">
    <column name="DepartmentId" />
  </key>
  <one-to-many class="Employee" />
</set>