Hi, I''m building an application where you can have friends like in myspace. Only if two people agree to be friends, a friendship relation should be established. If they agreed, it should be an undirected (aka symmetric, bidirectional) graph. I don''t want to keep two entries for each friendship like in the following table: table friendships parent | child user1 | user2 user2 | user1 I hope you understand what I mean. I want that if anybody of the two friends quit friendship, the relationship between the two also gets deleted. Thanks. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
What type of queries do you need to be able to do after this relationship is set up? For example Do Pam and Jeff have a friendship? List all the friends of Pam? List all the people who are not friends of Pam or Jeff? The best solution will depend on how you want to get to the data. steve -- 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 -~----------~----~----~----~------~----~------~--~---
Most basically I just want to query the friends of Pam. If Pam and Jeff are friends, i want to get Pam as friend of Jeff and Jeff as friend of Pam. For this I would have to keep two database entries for each friendship, like in the following example: user_id | friend_id id_of_pam | id_of_jeff id_of_jeff | id_of_pam I''d like to do it with one, but I don''t think there is an elegant solution, or is it? A wish of mine also would be to get the shortest connection between person A and person B, like in xing.com (single pair shortest path problem in graph theory), but I have no idea how to do that, and it''s not a necessity. Etherway, not having to keep two entries for each friendship (then you had also to monitor when a friendship gets deleted to also delete the other way round) would be favorable for this problem too. On Jun 11, 5:45 pm, Steve Rawlinson <rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org> wrote:> What type of queries do you need to be able to do after this > relationship is set up? For example > > Do Pam and Jeff have a friendship? > List all the friends of Pam? > List all the people who are not friends of Pam or Jeff? > > The best solution will depend on how you want to get to the data. > > steve > > -- > Posted viahttp://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 -~----------~----~----~----~------~----~------~--~---
> Most basically I just want to query the friends of Pam. > If Pam and Jeff are friends, i want to get > Pam as friend of Jeff > and Jeff as friend of Pam.If you only want to be able to say is Pam a friend of Jeff then you could assign each user a unique prime number and store the multiple of the primes in a separate ''friendship'' table. But that won''t help you list all the friends of Pam (unless you don''t mind iterating over every entry in the table). So, what exact queries do you want to be able to do? steve -- 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 for your advice, but unfortunately I would also like to select all friends of Pam at once. On Jun 11, 10:36 pm, Steve Rawlinson <rails-mailing-l...@andreas- s.net> wrote:> > Most basically I just want to query the friends of Pam. > > If Pam and Jeff are friends, i want to get > > Pam as friend of Jeff > > and Jeff as friend of Pam. > > If you only want to be able to say is Pam a friend of Jeff then you > could assign each user a unique prime number and store the multiple of > the primes in a separate ''friendship'' table. But that won''t help you > list all the friends of Pam (unless you don''t mind iterating over every > entry in the table). > > So, what exact queries do you want to be able to do? > > steve > > -- > Posted viahttp://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 for your advice, but unfortunately I would also like to select > all friends of Pam at once.I can''t think of a way of doing this with only one table entry. I''m surprised because I thought I would be able to. It''s an interesting problem and I''ll pass it on to some colleagues. steve -- 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 -~----------~----~----~----~------~----~------~--~---
No progress I''m afraid. You are aware that what you want is handled by Rails using has_and_belongs_to_many relationships? But it does use two entries in a table for each relationship, you just don''t have to actually handle the table yourself. steve -- 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 -~----------~----~----~----~------~----~------~--~---
Steve Rawlinson wrote:> >> Thanks for your advice, but unfortunately I would also like to select >> all friends of Pam at once. >> > > I can''t think of a way of doing this with only one table entry. I''m > surprised because I thought I would be able to. It''s an interesting > problem and I''ll pass it on to some colleagues. > > steve > >I did this in the following way (YMMV): class Person << AR::B has_many :relation_tos, :class_name => ''Relationship'', :foreign_key => ''related_from'' has_many :relation_froms, :class_name => ''Relationship'', :foreign_key => ''related_to'' has_many :related_tos, :through => :relation_tos, :source => :relatee, :select => "modtypes.*, relationships.relationship_type, relationships.notes" # This gets the key join table details as well has_many :related_froms, :through => :relation_froms, :source => :relator, :select => "modtypes.*, relationships.relationship_type, relationships.notes" # This gets the key join table details as well def related_types related_froms.find(:all) + related_tos.find(:all) end The downside is, there''s two db queries to get the related people. I did this ages ago, in my early days on Rails, so haven''t really looked to see whether it can be improved. Hope this helps Chris p.s. It''s not really a person class, since that sort of relationship isn''t reflexive -- e.g. think of uncle-nephew relationship. -- ---------------------------- http://autopendium.com Stuff about old cars --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
How about using sql? avoiding habtm or hm :through?
so given a table
table friends
int inviter_id
int Invitee_id
bool accepted
And only one entry per friendship.
then find all friends using...
find_by_sql(
''SELECT p.* FROM people p, friends f WHERE f.accepted =
''t'' AND
( (f.invitee_id = #{id} AND p.id = f.inviter_id) OR (f.inviter_id #{id} AND p.id
= f.invitee_id) )''
)
I haven''t tested this, but seems it should work in both directions.
On Jun 25, 3:38 pm, Chris T
<ctmailingli...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>
wrote:> Steve Rawlinson wrote:
>
> >> Thanks for your advice, but unfortunately I would also like to
select
> >> all friends of Pam at once.
>
> > I can''t think of a way of doing this with only one table
entry. I''m
> > surprised because I thought I would be able to. It''s an
interesting
> > problem and I''ll pass it on to some colleagues.
>
> > steve
>
> I did this in the following way (YMMV):
>
> class Person << AR::B
> has_many :relation_tos,
> :class_name => ''Relationship'',
> :foreign_key => ''related_from''
> has_many :relation_froms,
> :class_name => ''Relationship'',
> :foreign_key => ''related_to''
> has_many :related_tos,
> :through => :relation_tos,
> :source => :relatee,
> :select => "modtypes.*, relationships.relationship_type,
> relationships.notes" # This gets the key join table details as well
> has_many :related_froms,
> :through => :relation_froms,
> :source => :relator,
> :select => "modtypes.*, relationships.relationship_type,
> relationships.notes" # This gets the key join table details as well
>
> def related_types
> related_froms.find(:all) + related_tos.find(:all)
> end
>
> The downside is, there''s two db queries to get the related people.
I did
> this ages ago, in my early days on Rails, so haven''t really looked
to
> see whether it can be improved.
>
> Hope this helps
>
> Chris
> p.s. It''s not really a person class, since that sort of
relationship
> isn''t reflexive -- e.g. think of uncle-nephew relationship.
>
> --
> ----------------------------http://autopendium.com
> Stuff about old cars
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