How to query this database with DM query language?

gistfile1.txt

Here's the relevant part of the schema, simplified, showing relations:

CREATE TABLE "units" (
  "id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
  "name" VARCHAR(50)
);

CREATE TABLE "champions" (
  "unit_id" INTEGER NOT NULL,
  "title" VARCHAR(50),
  PRIMARY KEY("unit_id")
);

CREATE TABLE "structures" (
  "unit_id" INTEGER NOT NULL,
  "title" VARCHAR(50),
  PRIMARY KEY("unit_id")
);

"champions" and "structures" are both types of "units". This scheme is the inverse of normal polymorphic relationships. In ActiveRecord, units would polymorphically point at each subtype with a "type" column.

So:

class Champion
  property :unit_id, Integer, :key => true # not serial
  belongs_to :unit
end

class Structure
  property :unit_id, Integer, :key => true # not serial
  belongs_to :unit
end

The problem is that I have to do an explicit SQL join for the inverse relationship:

# This is nonsensical:
class Unit
  has 1, :champion, :structure, or whatever subtype
end

Rather, I need to accomplish a query like this:

SELECT *
  FROM units AS u
    LEFT OUTER JOIN structures AS s USING (unit_id)
    LEFT OUTER JOIN champions AS s USING (unit_id)
    [and all the other unit subtypes I add, eventually...]
WHERE u.name = 'Olga';

Is there any way to programmatically accomplish this kind of query without executing SQL in DM?