Question

Hi guys here is my code:

class Tailor < ActiveRecord::Base
    has_many    :tailor_items
    has_many    :order_items

    [:collars, :sexes, :sleeves].each do |attribute|
        has_many    attribute, through: :tailor_items, source: :item, source_type: attribute.to_s.classify

    end
 end

class TailorItem < ActiveRecord::Base
  belongs_to        :tailor
  belongs_to        :item, polymorphic: true
end

class Collar < ActiveRecord::Base
end

What I need to do is this:
For a given shirt I need to select a tailor. A shirt can have a collar, male/female or a certain type of sleeve. Some tailors can make all collars but only a few sleeves, others can make only male stuff, etc.
The priority doesnt matter for this example. The idea is that I end up with 1 tailor.

I tried this:

tailors = Tailor.joins(:tailor_items).where("(item_id = ? and item_type = ?)",1,"Collar")
if tailors.count > 1
  tailors.where("(item_id = ? and item_type = ?)",2,"Sleeve")
  if tailors.count > 1
     # and so forth.
  end
end

But I never get a row back.
If I say:

Tailor.find(1).tailor_items 

I get two results (sudo code for simplicity)

<id: 1, item_type: "Collar"><id:2, item_type:"Sleeve"> 

and for second tailor:

Tailor.find(2).tailor_items 

I get two results (sudo code for simplicity)

<id: 1, item_type: "Collar"><id:3, item_type:"Sleeve"> 

but when I try to chain them in the query its no worky…
Not even if I put it all in one where:

Tailor.where("(item_id = 1 and item_type = 'Collar') and (item_id = 2 and item_type = 'Sleeve')")

I still get 0 results.

Tailor.where("item_id = 1 and item_type = 'Collar'") returns: Tailor #1
Tailor.where("item_id = 2 and item_type = 'Sleeve'") returns: Tailor #1

but together they return nothing.

Tailor Load (0.0ms) SELECT "tailors".* FROM "tailors" INNER
JOIN "tailor_items" ON "tailor_items"."tailor_id" = "tailors"."id" WHERE ((tailo
r_items.item_id = 1 and tailor_items.item_type = 'Collar') and (tailor_items.ite
m_id = 2 and tailor_items.item_type = 'Sleeve'))

I am confused..

Thanks for your help.

I run:
Win XP
Postgresql
Rails 3.2.2

PS: The only thing missing to make this complete after a polymorphic join is a bit of XML. 😛 Otherwise its just not enterprise-y enough..

EDIT:
Implementing Rob di Marcos scope, I get this SQL:

SELECT "tailors".* FROM "tailors" WHERE 
(EXISTS(SELECT * FROM tailor_items WHERE tailor_items.item_id = 1 and tailor_items.item_type = 'Collar')) 
AND (exists(select * from tailor_items where tailor_items.item_id = 2 and tailor_items.item_type = 'Sleeve'))

This returns
2 tailors instead of only tailor 1 who can do both (while tailor 2 cant do sleeve #2)

Answer 1

The problem is that the where needs to match on two rows. I generally will use sub-queries to test for this. So something like

Tailor.where("exists (select 'x' from tailor_items where 
         tailor_id = tailors.id and tailor_items.item_id = ? and 
         tailor_items.item_type=?)", 1, 'Collar').
       where("exists (select 'x' from tailor_items where 
         tailor_id = tailors.id and tailor_items.item_id = ? and 
         tailor_items.item_type=?)", 2, 'Sleeve')

In this example, I have one sub-query for each tailor item I am looking for. I could easily make this a scope on Tailor like:

class Tailor
  # ....
  scope :with_item, lambda{ |item_id, item_type | 
      where("exists (select 'x' from tailor_items where 
     tailor_id = tailors.id and tailor_items.item_id = ? and 
     tailor_items.item_type=?)", item_id, item_type)
     }

and then be able to chain my Tailor request

Tailor.with_item(1, 'Collar').with_item(2, 'Sleeve')