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
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit https://groups.google.com/groups/opt_out.
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 <lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out.
On 15 February 2013 10:05, Lorenz Blackbird <lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> 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)You don''t need to do that. If you have a course in @course then its paragraphs are just @course.paragraphs. It is rare to have to use joins when working with Rails if you have got the associations right.> > This works, but I want to select an array containing only the ids of > paragraphs.I think this should work. @course.paragraphs.select( :id ) Colin> > 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out.
Colin Law wrote in post #1097096:>> Paragraph.joins(:course_paragraphs => :course) >> .where(''course_paragraphs.course_id'' => @course.id) > > You don''t need to do that. If you have a course in @course then its > paragraphs are just @course.paragraphs. It is rare to have to use > joins when working with Rails if you have got the associations right.You''re right. I tried to resolve my problem in a different way and I''m returned unintentionaly at the classic method with a long solution :)> I think this should work. > @course.paragraphs.select( :id )Unfortunately it gave the same problem. (:id) -> MySQL error (:paragraphs => :id) -> hexadecimal values I took the decision to keep the "hexadecimal" solution and adapt another bit of my code to have same values. In any case, thanks for the answer. -- 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out.
On Feb 15, 2013, at 10:12 AM, Colin Law wrote:> On 15 February 2013 10:05, Lorenz Blackbird <lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> 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) > > You don''t need to do that. If you have a course in @course then its > paragraphs are just @course.paragraphs. It is rare to have to use > joins when working with Rails if you have got the associations right. > >> >> This works, but I want to select an array containing only the ids of >> paragraphs. > > I think this should work. > @course.paragraphs.select( :id ) > > ColinActiveRecord actually gives you a method for exactly this: @course.paragraph_ids -Rob> >> >> 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org >> To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org >> 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org > 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out.
@p_ids = @course.paragraph_ids This solution works fine! Too simple for a C programmer like me :) Pluck gave me the same MySQL error. Thanks at all for the help. -- 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 rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit https://groups.google.com/groups/opt_out.