Question

I have a function that I want to write and cannot work out how it will work. The first line returns my steps in the order that they should be, and the second line I want to return the last matching step in all the steps for the course. I think I am close but need to know what I’ve done wrong.

course_steps_in_order = course.steps.sort_by(&:component_and_step_order)    
last_completed_step = current_user.completed_steps.where("steps.id in ?", course_steps_in_order).last

I am getting the error…

ActiveRecord::StatementInvalid: PG::Error: ERROR:  syntax error at or near "1"
LINE 1: ... WHERE "user_steps"."user_id" = 3 AND (step.id in 1,2,4,8,5,...
                                                         ^
: SELECT  "steps".* FROM "steps" INNER JOIN "user_steps" ON "steps"."id" = "user_steps"."step_id" WHERE "user_steps"."user_id" = 3 AND (step.id in 1,2,4,8,5,3,7,6,9) ORDER BY "steps"."id" DESC LIMIT 1

A course has many components which has many steps, as per the below models…

class Course < ActiveRecord::Base
  has_many :components, :dependent => :destroy, :order => "component_order"
  has_many :steps, :through => :components, :dependent => :destroy
end

class Component < ActiveRecord::Base
  belongs_to :course
  has_many :steps, :dependent => :destroy, :order => "step_order"
end

class Step < ActiveRecord::Base
  belongs_to :component

  def component_and_step_order
    component_order * 100 + step_order
  end
end

Answer 1

Add the collection-enclosing parenthesis:

...
last_completed_step = current_user.completed_steps.where("steps.id in (?)", course_steps_in_order).last

Now the query will generate correctly like so:

... AND (step.id in (1,2,4,8,5))