根据联接表中的条件获取Rails联接模型记录

Question

I'm wondering if there's a "proper" Rails (3.1) way to do this without just using a finder SQL.

I have an STI hierarchy:

class Party
class Person < Party
class Organisation < Party

Related parties are joined via a party_relationships table and model, with foreign keys party_id and related_party_id

I want to be able to do is this:

class Party
  # Should return all party_relationships where the related_party is a Person
  has_many :person_relationships

  # Should return all party_relationships where the related_party is an Organisation
  has_many :organisation_relationships
end

What's the best way of doing this in Rails 3.1?

Answer 1

Solved it. This works, and I have to say that I'm very impressed with the way the scopes and relationships work:

class Party
  has_many :party_relationships, foreign_key: :party_id
end

class PartyRelationship
  belongs_to :related_party, :class_name => 'Party'
  scope :to_organisations, :joins => :related_party, :conditions => {:parties => {:type => 'Organisation' } }
end

Now if I have a party...

@party.party_relationships                   # <- returns all relationships
@party.party_relationships.to_organisations  # <- Only those where related_party is an organisation

What I really like about this is that if I'd used :finder_sql on a has_many then the SQL would be in the Party class. This way keeps things properly encapsulated so that a Party doesn't have to know how the scope is implemented. Neat.