On Sunday, 15 June 2014 23:47:31 UTC-5, Ruby-Forum.com User wrote: > > Hassan Schroeder wrote in post #1149759: > > On Sun, Jun 15, 2014 at 1:29 AM, Ronald Fischer <li...@ruby-forum.com > <javascript:>> > > wrote: > > (assume that ) box = Box.find(box_id) > > > > box.cards # has the cards you want *if* you need all the attributes > > > > box.cards.pluck(:id) # builds a query to fetch *only* the card ids > > May I ask how this works (internally)? For pluck() to be applied, Ruby > has first to execute box.cards() to get an Array of the cards. Unless > the Card objects are implemented as proxies, which only fetch their data > from the database if one asks for it, I would at this point, at least > temporarily, have all the selected Card data in memory, isn't it? > > The short version: `box.cards` doesn't actually load the records until they are needed; that's why things like `box.cards.limit(10)` can work. `box.cards` returns a Relation, which *can* return records (if you call something on it that requires them, like `to_a` or `each`) but can also be used to construct SQL queries.
This is a bit tricky to see in the console, since typing `box.cards` there calls `inspect` on the Relation, which loads all the records. For more detail, see the source. --Matt Jones -- 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+unsubscr...@googlegroups.com. To post to this group, send email to rubyonrails-talk@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rubyonrails-talk/7204c876-da89-4027-b3c7-16a190900847%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
