You probably want #pluck: http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-pluck
-a. On 15 Feb 2013, at 5:05 AM, Lorenz Blackbird <[email protected]> wrote: > I have a many-to-many relationship in my course model in this way: > > has_many :course_paragraphs > has_many :paragraphs, :through => :course_paragraphs > > I use an inner join to select the paragraphs of my course: > > Paragraph.joins(:course_paragraphs => :course) > .where('course_paragraphs.course_id' => @course.id) > > This works, but I want to select an array containing only the ids of > paragraphs. > > By this solution I get an error: > > @p_ids = Paragraph.select(:id) > .joins(:course_paragraphs => :course) > .where('course_paragraphs.course_id' => @course.id) > > Mysql2::Error: Column 'id' in field list is ambiguous: SELECT id FROM > `paragraphs` INNER JOIN `course_paragraphs` ON > `course_paragraphs`.`paragraph_id` = `paragraphs`.`id` INNER JOIN > `courses` ON `courses`.`id` = `course_paragraphs`.`course_id` WHERE > `course_paragraphs`.`course_id` = 1 > > By this solution, the array contain hexadecimal values: > > @p_ids = Paragraph.select('paragrahs.id') > .joins(:course_paragraphs => :course) > .where('course_paragraphs.course_id' => @course.id) > > Where in my problem? > > Thanks to all. > > -- > Posted via http://www.ruby-forum.com/. > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Talk" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > For more options, visit https://groups.google.com/groups/opt_out. > > -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
