Filtering entities by subtype with NHibernate.Linq

Question

Given this inheritance mapping:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
    <class name="User" table="[User]" abstract="true">
        <joined-subclass name="SubUser1" table="SubUser1">
            <key column="UserId" />
            ...
        </joined-subclass>
        <joined-subclass name="SubUser2" table="SubUser2">
            <key column="UserId" />
            ...
        </joined-subclass>
        <joined-subclass name="SubUser3" table="SubUser3">
            <key column="UserId" />
            ...
        </joined-subclass>
    </class>
</hibernate-mapping>

how do I query for all instances of SubUser2 and SubUser3? I realize I can do this:

session.Linq<User>().OfType<SubUser2>()

but that only allows me to filter by a single type. I tried this:

session.Linq<User>().Where(user => user is SubUser2)

but that resulted in this error:

could not resolve property:  of: User

Any ideas on how to express a query against multiple sub-types?

Answer 1

As far as I can tell, this is not possible. Perhaps it will be in the future. I know they accept patches :-)

I only have about 500 records and 4 types, and am usually querying on 2 or 3 types at the same time. For now, I am applying the filter on each type in the database, then concatenating the result sets and doing ordering and paging in-memory.

It is not the most efficient solution, but works just fine. I chose not to add a superfluous discriminator column to the User table solely to enable this query.

Answer 2

What about something like this:

// Get them in 2 queries
var sub2 = session.Linq<SubUser2>().Select(x => x).ToList();
var sub3 = session.Linq<SubUser3>().Select(x => x).ToList();

// Join together in memory
var sub2And3 = sub2.OfType<User>().Union( sub3.OfType<User>() );