I have two "top-level" entities joined with a third table (many-to-many
relationship) which uses yet another table (lookup/reference table) to
describe the nature of the relationship of the join. ActiveRecord is
adding an unnecessary JOIN which results in duplicate rows being returned.
[See model class definitions below.]
# users INNER JOIN request_user_roles INNER JOIN request_role_types
@request.users.count # 1
# users INNER JOIN request_user_roles INNER JOIN request_role_types INNER
JOIN request_user_roles
@request.users.is_request_initiator.count # 898
@request.users.is_request_initiator.uniq.count # 1
# users INNER JOIN request_user_roles INNER JOIN request_role_types INNER
JOIN request_user_roles
@request.users.joins(:request_role_types).merge(RequestRoleType.is_initiator).count
# 898
I want to select users for a particular request based on their role with
respect to it.
I can write this in SQL, and I can write this in a single AR query, but I
would like to simplify my code
with scopes, if possible. What I can't do is structure a scope such that I
don't return duplicates. Or,
to put it another way, I can't structure the scope to not automatically
include the extra JOIN (on request_user_roles).
Is there a way to express this with AR scopes or in another modular,
re-usable way? The uniq() feels dirty.
# relevant classes
# User
# |
# RequestUserRole - RequestRoleType
# |
# Request
class User < ActiveRecord::Base
has_many :request_user_roles
has_many :requests, :through => :request_user_roles
has_many :request_role_types, :through => :request_user_roles
scope :is_request_initiator,
joins(:request_role_types).where(:request_role_types => {:request_role_type
=> 'Initiator'})
end
class Request < ActiveRecord::Base
has_many :request_user_roles
has_many :users, :through => :request_user_roles
has_many :request_role_types, :through => :request_user_roles
end
class RequestUserRole < ActiveRecord::Base
belongs_to :user
belongs_to :request
belongs_to :request_role_type
end
class RequestRoleType < ActiveRecord::Base
has_many :request_user_roles
scope :is_initiator, where(:request_role_type => 'Initiator')
end
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