Rails - Jul 2011 - STI joins

I have 2 models set up using single table inheritance (STI) with belongs_to
relationships to a third model.

class CoveredEntity < Entity
	belongs_to :breach
		...
end

class BusinessAssociate < Entity
	belongs_to :breach
		...
end

class Breach < ActiveRecord::Base
	has_one :covered_entity
	has_one :business_associate
end


In my index view for breaches controller I am displaying the covered_entity.name
and the business_associate.name (if it exists).  I want to allow the users to
sort the index table by either of these values; however, since they use STI and
are the same table, just doing
@breaches.includes(:covered_entity).includes(:business_associate).order("#{sort_column}
#{sort_direction}") does not work.

I can get around this by using .joins("inner join (select * from entities
where entities.type = ''CoveredEntity'') as covered_entities
left join (select * from entities where entities.type =
''BusinessAssociate'') as business_associates) and then I am
able to use .order("business_associate.name") or
.order("covered_entities.name") and get the desired results.

I was curious if there is another way to do this that would not require me to
write out the joins by hand ( passing an alias to association or includes for
example).

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On Friday, July 22, 2011 7:12:07 AM UTC-6, Juan Alvarado
wrote:
>
> I have 2 models set up using single table inheritance (STI) with belongs_to
> relationships to a third model.  
>
> class CoveredEntity < Entity
> belongs_to :breach
> ...
> end
>
> class BusinessAssociate < Entity
> belongs_to :breach
> ...
> end
>
> class Breach < ActiveRecord::Base
> has_one :covered_entity
> has_one :business_associate
> end
>
>
> In my index view for breaches controller I am displaying the 
> covered_entity.name and the business_associate.name (if it exists).  I 
> want to allow the users to sort the index table by either of these values; 
> however, since they use STI and are the same table, just doing 
>
@breaches.includes(:covered_entity).includes(:business_associate).order("#{sort_column}
> #{sort_direction}") does not work.  
>
> I can get around this by using .joins("inner join (select * from
entities
> where entities.type = ''CoveredEntity'') as
covered_entities left join (select
> * from entities where entities.type =
''BusinessAssociate'') as
> business_associates) and then I am able to use .order("
> business_associate.name") or .order("covered_entities.name")
and get the
> desired results.
>
> I was curious if there is another way to do this that would not require me 
> to write out the joins by hand ( passing an alias to association or
includes
> for example).
>
Any reason why you can''t use something like this?

  sort_by_name_of = use_business_entity ? :business_associate : 
:covered_entity
  @breaches = @breaches.joins(sort_by_name_of).order(:name) if sort_by_name
  # works in my quick, test rails 3.0.7 app

Is using #joins abhorrent to you?

Also, as an aside, any reason you don''t/can''t put your
"belongs_to :breach"
relationship in your Entity class (since both STI sub-types both have the 
relationship of the same name)?

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