unique in .hbm.xml file not raising exception 
I am having the following in my .hbm.xml file

    <?xml version="1.0" encoding="utf-8" ?>
    <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    									namespace="Core.Domain.Model"
    									assembly="Core">
    
      <class name="Category" table="Categories" dynamic-update="true">
        <cache usage="read-write"/>
        <id name="Id" column="Id" type="Guid">
          <generator class="guid"/>
        </id>
        <property name="Name" length="100">
        <column name="Name" unique="true" index="IX_Category"/>
        </property>
      </class>
    </hibernate-mapping>


----------
I am having the following code, however, I can see that no exception is being raised when I am inserting a duplicate value for the Name field. Why is that so? 

     void IRepository<Category>.Save(Category entity)
            {
                using (var scope = new TransactionScope(TransactionScopeOption.Required))
                {
                using (ISession session = NHibernateHelper.OpenSession())
                {
                    using (ITransaction transaction = session.BeginTransaction())
                    {
                        session.Save(entity);
                        transaction.Commit();
                    }
                }
                scope.Complete();
                }    
            }
unique in .hbm.xml file not raising exception 
===

I am having the following in my .hbm.xml file

    <?xml version="1.0" encoding="utf-8" ?>
    <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
    									namespace="Core.Domain.Model"
    									assembly="Core">
    
      <class name="Category" table="Categories" dynamic-update="true">
        <cache usage="read-write"/>
        <id name="Id" column="Id" type="Guid">
          <generator class="guid"/>
        </id>
        <property name="Name" length="100">
        <column name="Name" unique="true" index="IX_Category"/>
        </property>
      </class>
    </hibernate-mapping>


----------
I am having the following code, however, I can see that no exception is being raised when I am inserting a duplicate value for the Name field. Why is that so? 

     void IRepository<Category>.Save(Category entity)
            {
                using (var scope = new TransactionScope(TransactionScopeOption.Required))
                {
                using (ISession session = NHibernateHelper.OpenSession())
                {
                    using (ITransaction transaction = session.BeginTransaction())
                    {
                        session.Save(entity);
                        transaction.Commit();
                    }
                }
                scope.Complete();
                }    
            }