Isn't the case where a simple "group by X having count(*) = 2" could handle the problem ?
Arel can achieve this query easily. On Wed, Aug 8, 2012 at 2:27 PM, Pedro Nascimento <pnascime...@gmail.com>wrote: > Take a look at ARel and Squeel gem. Squeel gem supports something like > this already. > > On Wed, Aug 8, 2012 at 12:05 PM, Rafael Almeida <almeida...@gmail.com>wrote: > >> Hello. >> >> Let's say I have the following schema >> >> People <---> people_services <---> services >> >> That is, people has a many-to-many relationship with services. Say I want >> to find all people who has services of types 1 and 2. How can we do it on >> activerecord today? >> >> My best solution so far is this >> >> people_query = Person.joins(:services) >> people = [] >> [1,2].each do |t| >> people << people_query.where(:type => 1) >> end >> people = people.reduce(:&) >> >> That's not so good because by doing reduce(:&) you're exiting >> activerecord domain. So you wouldn't be able to do something like >> people.reduce(:&).limit(10). Also, that way I'm loading a lot more data >> than I actually need in my application memory. So, certainly not optimal >> solution. >> >> It's possible to make such query in SQL alone, if the dbms supports >> INTERSECTION then doing it is straightforward. If it doesn't, it's still >> possible using joins on subqueries. >> >> I think activerecord ought support such query and I'm willing to take my >> time and write the code for it. However, I'd like someone to help me out >> with it a bit. I don't understand rails or activerecord code base so well. >> Anyway, it would be best if I did a gem that introduces that feature into >> activerecord. Can anyone tell me what should I look up? A high level >> description of what I must do would be great. Something like "You'll need >> to create a gem, monkey patch this activerecord class, probably use this >> and this function to help you writing your SQL" would be nice. >> >> Cheers >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Ruby on Rails: Core" group. >> To view this discussion on the web visit >> https://groups.google.com/d/msg/rubyonrails-core/-/jz3f6lJrXEkJ. >> To post to this group, send email to rubyonrails-core@googlegroups.com. >> To unsubscribe from this group, send email to >> rubyonrails-core+unsubscr...@googlegroups.com. >> For more options, visit this group at >> http://groups.google.com/group/rubyonrails-core?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Core" group. > To post to this group, send email to rubyonrails-core@googlegroups.com. > To unsubscribe from this group, send email to > rubyonrails-core+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/rubyonrails-core?hl=en. > -- Att, Everton http://www.evertonmoreth.com.br -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To post to this group, send email to rubyonrails-core@googlegroups.com. To unsubscribe from this group, send email to rubyonrails-core+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-core?hl=en.
