How to map this class in NHibernate (not FluentNHibernate)?

Question

Suppose I have a database like this:

This is set up to give role-wise menu permissions.

Please note that, User-table has no direct relationship with Permission-table.

Then how should I map this class against the database-tables?

class User
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public string Username { get; set; }
        public string Password { get; set; }
        public bool? IsActive { get; set; }

        public IList<Role> RoleItems { get; set; }
        public IList<Permission> PermissionItems { get; set; }
        public IList<string> MenuItemKeys { get; set; }
    }

This means,

(1) Every user has some Roles.

(2) Every user has some Permissions (depending on to Roles).

(3) Every user has some permitted MenuItemKeys (according to Permissions).

How should my User.hbm.xml look like?

Answer 1

Roles and Permissions are likely to be accessed a lot in the application. They are very likely to be in the second level cache, which means we can expect to efficiently iterate the User.RoleItems and Role.Permissions.

This has the advantage that we can generally expect to perform no queries when iterating those collections.

You could map the classes as follows.

The properties User.PermissionItems and User.MenuItemKeys are derived from the persistent entities, and thus do not appear in the mappings.

<class name="User" table="user">
  <id name="ID">
    <generator class="native"/>
  </id>
  <property name="Name"/> 
  <property name="Username"/>
  <property name="Password"/>
  <property name="IsActive"/>

  <bag name="RoleItems" table="userrole" lazy="true">
    <key column="userid" />
    <many-to-many class="Role" column="roleid"/>
  </bag>
</class>

<class name="Role" table="role">
  <id name="ID">
    <generator class="native"/>
  </id>
  <property name="RoleName"/>
  <property name="IsActive"/>

  <bag name="Permissions" table="permission">
    <key column="roleid" />
    <one-to-many class="Permission"/>
  </bag>
</class>

<class name="Permission" table="permission">
  <id name="ID">
    <generator class="native"/>
  </id>
  <property name="MenuItemKey"/>
</class>

I would make the 2 additional lists you had on User into derived enumerations. If they were lists, there is no unambiguous way to insert into them since you cannot know to which role the value applies. Also, a Role is not owned by a User.

Update: now using Diego's improved version of these properties.

class User
{
    public virtual IEnumerable<Permission> PermissionItems
    {
        get {
            return RoleItems.SelectMany(role => role.PermissionItems);
        }
    }

    public virtual IEnumerable<string> MenuItemKeys
    {
        get {
            return RoleItems.SelectMany(role => role.PermissionItems,
                        (role, permission) => permission.MenuItemKey);
        }
    }
}

Answer 2

The mapping posted by Lachlan is the best alternative. You could use queries that perform all the joins for each collection, but that'd make them read only for practical purposes.

There is a much easier way to implement the property code, however, that might help you decide:

public IEnumerable<Permission> PermissionItems
{
    get
    {
        return RoleItems.SelectMany(role => role.PermissionItems);
    }
}

public IEnumerable<string> MenuItemKeys
{
    get
    {
        return RoleItems.SelectMany(role => role.PermissionItems,
                                   (role, permission) => permission.MenuItemKey);
    }
}