Hi everybody,
I am working on an app and I need the following behavior :
A :has_many B
A :has_many C :though B
and
C :has_many B
C has_many A :through B
My goal is to find all the A objects that are related to a given
''a''
object, based on the fact that they have some Cs in common;
Here is how I''d do it :
related = []
a.cs.each do |c|
related << c.as
end
related.uniq!
I am pretty sure this is not the good solutions : it makes a lot of
request, and there is just now way to "Order" the related objects by
the
number of cs they have in common with a!
Anyone has a better idea on how to do it?
Thanks!
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On 20 May 2008, at 21:42, Julien Genestoux wrote:> > Hi everybody, > > I am working on an app and I need the following behavior : > > A :has_many B > A :has_many C :though B > > and > C :has_many B > C has_many A :through B > > My goal is to find all the A objects that are related to a given ''a'' > object, based on the fact that they have some Cs in common; >Well the sql is probably along the lines of Foo.find_by_sql( <<_SQL) select related_foos.* from foos inner join bs on bs.foo_id = foos.id inner join cs on bs.c_id = cs.id inner join bs as second_bs on second_bs.c_id = cs.id inner_join foos as related_foos on related_foos.id = second_bs.foo_id WHERE foos.id = 123 _SQL (i''ve swapped A for Foo) You could probably also do it via A.find :all, :joins => {:b => {:c => {:b => :a}}} but you''d have to remember how activerecord generates table aliases in order to write your select clause. Fred> Here is how I''d do it : > > related = [] > a.cs.each do |c| > related << c.as > end > related.uniq! > > I am pretty sure this is not the good solutions : it makes a lot of > request, and there is just now way to "Order" the related objects by > the > number of cs they have in common with a! > > Anyone has a better idea on how to do it? > > Thanks! > -- > 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 post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Thankx Frederick! That is excactly what I needed... However, I''ve got 2 questions : performance: good, bad, vey bad? And also, is there any way to "order" the list of related by number of common Cs? Thanks again, that''s helpful anyway! Frederick Cheung wrote:> On 20 May 2008, at 21:42, Julien Genestoux wrote: > >> C has_many A :through B >> >> My goal is to find all the A objects that are related to a given ''a'' >> object, based on the fact that they have some Cs in common; >> > > Well the sql is probably along the lines of > > Foo.find_by_sql( <<_SQL) > select related_foos.* from foos > inner join bs on bs.foo_id = foos.id > inner join cs on bs.c_id = cs.id > inner join bs as second_bs on second_bs.c_id = cs.id > inner_join foos as related_foos on related_foos.id = second_bs.foo_id > WHERE foos.id = 123 > _SQL > > (i''ve swapped A for Foo) > > You could probably also do it via > > A.find :all, :joins => {:b => {:c => {:b => :a}}} > but you''d have to remember how activerecord generates table aliases in > order to write your select clause. > > Fred-- 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 post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
On 20 May 2008, at 23:40, Julien Genestoux wrote:> > Thankx Frederick! > > That is excactly what I needed... However, I''ve got 2 questions : > performance: good, bad, vey bad?4 joins like that is probably not going to be super great but it''s not going to be the end of the world. Benchmark it and find out> > And also, is there any way to "order" the list of related by number of > common Cs? >nothing that I can think of off the top of my head.> Thanks again, that''s helpful anyway! > > > > Frederick Cheung wrote: >> On 20 May 2008, at 21:42, Julien Genestoux wrote: >> >>> C has_many A :through B >>> >>> My goal is to find all the A objects that are related to a given ''a'' >>> object, based on the fact that they have some Cs in common; >>> >> >> Well the sql is probably along the lines of >> >> Foo.find_by_sql( <<_SQL) >> select related_foos.* from foos >> inner join bs on bs.foo_id = foos.id >> inner join cs on bs.c_id = cs.id >> inner join bs as second_bs on second_bs.c_id = cs.id >> inner_join foos as related_foos on related_foos.id = second_bs.foo_id >> WHERE foos.id = 123 >> _SQL >> >> (i''ve swapped A for Foo) >> >> You could probably also do it via >> >> A.find :all, :joins => {:b => {:c => {:b => :a}}} >> but you''d have to remember how activerecord generates table aliases >> in >> order to write your select clause. >> >> Fred > > -- > 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 post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
Thanks again Frederick!!
One last thing :
A.find :all, :joins => {:b => {:c => {:b => :a}}} gives all the
element
that are related to any other element. Is there any way to have the same
thing with a specific element, without using the MySQL?
Thanks!
Frederick Cheung wrote:> On 20 May 2008, at 23:40, Julien Genestoux wrote:
>
>>
>> Thankx Frederick!
>>
>> That is excactly what I needed... However, I''ve got 2
questions :
>> performance: good, bad, vey bad?
>
> 4 joins like that is probably not going to be super great but it''s
not
> going to be the end of the world. Benchmark it and find out
>>
>> And also, is there any way to "order" the list of related by
number of
>> common Cs?
>>
> nothing that I can think of off the top of my head.
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On 21 May 2008, at 00:08, Julien Genestoux wrote:> > Thanks again Frederick!! > > One last thing : > > A.find :all, :joins => {:b => {:c => {:b => :a}}} gives all the > element > that are related to any other element. Is there any way to have the > same > thing with a specific element, without using the MySQL? >You just need to stick the appropriate conditions in (but to do that properly you need to remember how activerecord aliases tables (so that you can disambiguate between the first and the second join of a) and I can''t remember the rules off the top of my head. Fred> Thanks! > > > > > Frederick Cheung wrote: >> On 20 May 2008, at 23:40, Julien Genestoux wrote: >> >>> >>> Thankx Frederick! >>> >>> That is excactly what I needed... However, I''ve got 2 questions : >>> performance: good, bad, vey bad? >> >> 4 joins like that is probably not going to be super great but it''s >> not >> going to be the end of the world. Benchmark it and find out >>> >>> And also, is there any way to "order" the list of related by >>> number of >>> common Cs? >>> >> nothing that I can think of off the top of my head. > > -- > 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 post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---