配置文件

Customer.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="Entity.CustomerEntity, Entity" table="Customer" lazy="false" >
    <id name="CustomerID" column="CustomerID" type="Int32">
      <generator class="identity" />
    </id>
    <property name="CustomerName" column="CustomerName" type="String" length="10" />
    <bag name="Files" table="File" cascade="all">
      <key column="FileID" foreign-key="FileID"></key>
      <one-to-many class="Entity.FileEntity, Entity"/>
    </bag>
  </class>
</hibernate-mapping>

File.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="Entity.FileEntity, Entity" table="File1"  lazy="false">
    <id name="FileID" column="FileID" type="Int32">
      <generator class="identity" />
    </id>
    <property name="FileSize" column="FileSize" type="Int32" length="4" />
    <property name="CustomerID" column="CustomerID" type="Int32" length="4" />
    <many-to-one name="Customer" column="CustomerID" class="Entity.CustomerEntity, Entity" insert="false"/>
    <bag name="DownloadLogs" table="DownloadLog" cascade="all">
      <key column="FileID"/>
      <one-to-many class="Entity.DownloadLogEntity, Entity" />
    </bag>
  </class>
</hibernate-mapping>

DownloadLog.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="Entity.DownloadLogEntity, Entity" table="DownloadLog" lazy="false" >
    <id name="DownloadLogID" column="DownloadLogID" type="Int32">
      <generator class="identity" />
    </id>
    <property name="FileID" column="FileID" type="Int32" length="4" />
    <property name="Times" column="Times" type="Int32" length="4" />
    <many-to-one name="File" column="FileID" class="Entity.FileEntity, Entity" insert="false"/>
  </class>
</hibernate-mapping>

从配置文件上可以看出
每个customer对应多个file，每个file对应多个downloadlog
如果使用icriteria查询customer对应的downloadlog
可以这样写：

public IList<DownloadLogEntity> GetByCustomerID(int customerID)
{
  ICriteria criteria = NHibernateSession.CreateCriteria(typeof(DownloadLogEntity));
  criteria.CreateAlias("File", "file");
  criteria.CreateAlias("file.Customer", "customer");
  criteria.Add(Expression.Eq("customer.CustomerID",customerID));
  return criteria.List<DownloadLogEntity>();
}