Hey all,
This example of working code:
@a = @b.where(:a_group_id.ne => nil).collect { |b| b.a_group }
doesn''t make too much sense to me. For one, I am not sure what that
"ne" is doing there. Is this a postgresql thing? Second, it looks like
we are collecting active record objects where the a_group_id is null,
collecting them in an array and then invoking the a_group association
method on it to get its association. That doesnt make sense because
the fact that we collected objects which had no association, how can
we invoke the association method on it?
thanks for response
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John Merlino wrote in post #1021280:> Hey all, > > This example of working code: > > @a = @b.where(:a_group_id.ne => nil).collect { |b| b.a_group } > > doesn''t make too much sense to me. For one, I am not sure what that > "ne" is doing there. Is this a postgresql thing? Second, it looks likeThe "ne" is Arel''s version of "Not Equal." So that''s ":a_group_id not equal to nil"> we are collecting active record objects where the a_group_id is null, > collecting them in an array and then invoking the a_group association > method on it to get its association. That doesnt make sense because > the fact that we collected objects which had no association, how can > we invoke the association method on it?@a will contain a collection of the associated objects for records where the associated object exists (is not nil). -- 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-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
thanks for response. What you said explained a lot. Now I have never seen rails code written like that. Would it have been better to do this: @b.map(&:a_group).compact.uniq On Sep 11, 11:32 am, Robert Walker <li...-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:> John Merlino wrote in post #1021280: > > > Hey all, > > > This example of working code: > > > @a = @b.where(:a_group_id.ne => nil).collect { |b| b.a_group } > > > doesn''t make too much sense to me. For one, I am not sure what that > > "ne" is doing there. Is this a postgresql thing? Second, it looks like > > The "ne" is Arel''s version of "Not Equal." So that''s ":a_group_id not > equal to nil" > > > we are collecting active record objects where the a_group_id is null, > > collecting them in an array and then invoking the a_group association > > method on it to get its association. That doesnt make sense because > > the fact that we collected objects which had no association, how can > > we invoke the association method on it? > > @a will contain a collection of the associated objects for records where > the associated object exists (is not nil). > > -- > 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-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
On Sep 11, 2011, at 11:45 AM, John Merlino wrote:> thanks for response. What you said explained a lot. > > Now I have never seen rails code written like that. Would it have been > better to do this: > > @b.map(&:a_group).compact.uniq >That would load up all of the elements -- whether they matched (not nil) or not, and then filter them, so it''s kind of wasteful. Doing it all in Arel like that means that when the final SQL is compiled out of your Ruby method chain, the actual request to the DB will only return the resources you wanted, rather than also returning non-matching results. Walter -- 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-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
On Sun, Sep 11, 2011 at 5:18 PM, Walter Lee Davis <waltd-HQgmohHLjDZWk0Htik3J/w@public.gmane.org> wrote:> On Sep 11, 2011, at 11:45 AM, John Merlino wrote: > >> thanks for response. What you said explained a lot. >> >> Now I have never seen rails code written like that. Would it have been >> better to do this: >> >> @b.map(&:a_group).compact.uniq >>Depends. What that does is pull back all the results and then compact/uniq them in ruby -- whereas adding the where clause in the first example limits the number of rows brought back from the database. If there are a lot of rows in the database (1000''s or maybe even millions of rows) this may be a substantial difference. If there are a few hundred or less rows, it doesn''t make that big of a difference. But in general, I''d say that an approach that limits what''s brought back from the database is probably better. Kevin Bedell Boston Agile Partners @kbedell -- 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-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
thanks for responses -- 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-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.