将具有多级联接的SQL转换为Rails ActiveRecord表达式

Question

'SELECT "complaints".* FROM "complaints" INNER JOIN "machines" ON "machines"."id" = "complaints"."machine_id" INNER JOIN "mclns" ON "machines"."mcln_id" = "mclns"."id" ORDER BY "mclns"."response_time" ASC'

I need the above sql to be converted to Active record statement

complaint model does not know about mcln it has to go through machine

Complaint.joins(:machine=>:mcln) gives

SELECT "complaints".* FROM "complaints" INNER JOIN "machines" ON "machines"."id" = "complaints"."machine_id" INNER JOIN "mclns" ON "mclns"."machine_id" = "machines"."id"

but I need

SELECT "complaints".* FROM "complaints" INNER JOIN "machines" ON "machines"."id" = "complaints"."machine_id" INNER JOIN "mclns" ON "machines"."mcln_id" = "mclns"."id" 

Update:

A machine can have a mcln and also many machines can have same mcln.

I have implemented it by using

has_one :mcln on Machine model and belongs_to :machine on Mcln

And I'm not sure if thats correct implementation.

Answer 1

try out this :

SELECT complaints.*,machines.*,mclns.* FROM `complaints` 
INNER JOIN `machines` 
ON ( machines.id = complaints.machine_id )
INNER JOIN `mclns`
( ON machines.mcln_id = mclns.id )

Answer 2

Your association is incorrect. If many machines can have the same mcln then the machines table should have a mcln_id column and your classes should look like

class Machine < AR::Base
  belongs_to :mcln
end

class Mcln < AR::Base
  has_many :machines
end

Then Complaint.joins(:machine => :mcln) should generate the SQL you want