class File
{
public Guid Id
public string FileName

}
class FileToUsers
{
public Guid Id
public Guid FileId
public Guid UserId
public bool Archived
}
class Users
{
public Guid Id
public string FirstName
public string LastName
}

<class name="DataAccess.Domain.MemberMessages,DataAccess"  table="MemberMessages" lazy="false">
        <id name="Id" column="ID">
            <generator class="guid"/>
        </id>
        <property name="MemberId" column="MemberId"/>
        <property name="TimeStamp" column="TimeStamp"/>
        <property name="MessageText" column="MessageText"/>
        <property name="Archived" column="Archived"/>
        <property name="Deleted" column="Deleted"/>
        <many-to-one name="Message" column="MessageId" 
      class="DataAccess.Domain.Message, DataAccess"  />

    </class>


<class name="DataAccess.Domain.Message,DataAccess"  table="Message" lazy="false">
        <id name="Id" column="ID">
            <generator class="guid"/>
        </id>
        <property name="Name" column="Name"/>
        <property name="Description" column="Description"/>
        <property name="TimeStamp" column="TimeStamp"/>
        <property name="Length" column="Length"/>
        <property name="Content" column="Content"/>
        <property name="Icon" column="Icon"/>


        <bag name="Members"  table="MemberMessages" >
            <key column="Message"/>
            <one-to-many class="DataAccess.Domain.MemberMessages, DataAccess"/>
        </bag>
    </class>

Message mess = new Message();
            mess.Name = "sds";

            // add members
            MemberMessages mem = new MemberMessages();
            mem.MemberId = new Guid(DropDownListMembers.SelectedValue);
            mem.TimeStamp = DateTime.Now;


            mess.Members.Add(mem);
            // save message with members
            session.Save(mess);

            session.Flush();