Mapping Join Table that contains multiple joins

[predhead]

I have a legacy table that acts as a join table between multiple tables. For example if I have tables for people, dogs, cars, houses, etc. then there is just one table "relationships" that maps the many to many relationships for:
people to dogs
people to people
people to cars
cars to houses
etc...

The join table has two ids, as well as a value that indicates the type of relationship, for example:
people_dogs
people_people
people_cars
cars_people
....


I don't mind creating separate domain classes for each relationship if I have to, but how I do I tell it to only pull the values out of the join table based on the "type"?

Is there any way do to this? BTW this data is all read-only, I don't ever do saves, updates or deletes so cascading is irrelevant,.