Nhibernate更新不会持久化对数据库的更改

我在使用NHibernate将对数据对象的更改恢复到数据库中时遇到问题。我没有例外,所以很难知道去哪里找。有什么建议吗?

string name = "somenewname";
string repositoryId = "somerepositoryid";

ISession nhbSession = GetNhbSession(session);
nhbSession.Transaction.Begin();
try
{
    RepositoryDto existingRepository = nhbSession.Get<RepositoryDto>(repositoryId);
    if (existingRepository == null || existingRepository.TimeDeleted != null)
        throw new Exception("Repository does not exist in system or is deleted. Cannot modify.");

    existingRepository.Name = name; //works fine up to here as expected; is in DB with old name
    nhbSession.Update(existingRepository);
    nhbSession.Transaction.Commit();
}
catch (Exception ex)
{
    nhbSession.Transaction.Rollback();
    throw new Exception("Error modifying repository: " + ex.Message, ex);
}


<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="SomeComponent"
  namespace="SomeComponent.Repository.DTO" auto-import="true" default-lazy="false">
  <class name="RepositoryDto" table="Repository" mutable="false">  
    <id name="RepositoryId" column="repositoryId" unsaved-value="0">
      <generator class="assigned"/>
    </id>
    <property name="SystemId" column="systemId" not-null="true" />
    <property name="TimeCreated" column="timeCreated" not-null="true" />
    <property name="TimeDeleted" column="timeDeleted" not-null="false" />
    <property name="Name" column="name" not-null="true" />
  </class>
</hibernate-mapping>