Regardless of whether or not it might be a nice idiomatic style to be able to have, I think this discussion comes back around to what a lot of others ones on this list do as well: the change would be a pretty big potentially breaking change to existing code. So there's no real good reason to make the change to existing functionality.
Also, this could introduce many unexpected consequences (even ignoring the potential n+1 queries) given that the DB isn't locked around access. So unlike a prefetched array result set, what's in the "list" could change underneath you which would certainly be unexpected behavior. On Fri, Jul 19, 2013 at 11:12 AM, Michael Swan <[email protected]> wrote: > My thoughts for this are divorced from the "all" method. It was just my > poor example of a query. Perhaps, a better example would be: > User.where('age > 18')[4] > > or as suggested, ranges could be used as well: > User.where('age > 18')[0...5] > > Perhaps the only problem that I see, is if someone stores a query and then > iterates over the results using this method, they will likely result in > unnecessary load. I guess if this were to be a feature, one would have to > keep this in mind, and gems may have to account for it. I am not sure yet > if it could work without negatively affecting much. I would think that if > the '[]' function is called on a single query instance, multiple times, > passing in a single integer, that would indicate that the user is expecting > a different behavior. Still, it is very possible that this would also be > unreasonable. > > On Friday, July 19, 2013 7:40:27 AM UTC-4, James Coleman wrote: >> >> The whole point of the `all` method is that it actually fires the query >> on the current relation. So 1.) a change like this could potentially break >> a lot of existing code and 2.) it would defeat the point of the method. So >> I strongly believe that it shouldn't change. If you want the limit/offset >> query, use those methods. That's why they're there. >> >> >> On Fri, Jul 19, 2013 at 12:14 AM, Michael Swan <[email protected]> wrote: >> >>> Your example would involve three queries, each only allocating memory >>> and transferring content from the DBMS for 1 result, instead of every >>> record in the table. >>> >>> In the present: >>> User.all[5] # SELECT "users".* FROM "users" -> 420,000 results >>> >>> My suggestion: >>> User.all[5] # SELECT "users".* FROM "users" LIMIT 1 OFFSET 5 -> 1 result >>> >>> If I understand right, every User is pulled from the database, an array >>> is created with every single possible instance of a User, and then you >>> select a specific value from that array. I am thinking about this in the >>> context of any query. If you want the nth result from that query, it would >>> be nice to have an idiomatic shorthand for that, instead of >>> ".offset(n).first". >>> >>> It appears that even if you are iterating over the elements in a query >>> in such a way, my suggestion would improve performance. This has nothing to >>> do with any of the other functions that are delegated to Array. This is for >>> an ActiveRecord query that one is looking for the nth element within those >>> query results. >>> >>> No one in their right mind would use the delegated '[]' function on a >>> query that could have thousands of results. But they would call the '[]' >>> function that I am suggesting. >>> >>> On Friday, July 12, 2013 1:28:18 PM UTC-4, Olly Smith wrote: >>>> >>>> What do you expect to happen if the code looks like this: >>>> >>>> User.all[5] >>>> User.all[6] >>>> User.all[7] >>>> >>>> Should ActiveRecord make three separate queries? How about if the code >>>> iterates from index 100 to 200? >>>> >>>> Imho, it's totally acceptable to sacrifice 'idiomatic' ruby in this >>>> case in favour of fewer accidental gotchas. >>>> >>>> Olly >>>> On 12 Jul 2013 17:29, "Michael Swan" <[email protected]> wrote: >>>> >>>>> I am going to make this quick. Try something like: User.all[5] >>>>> Rails presently runs the following query in Postgres: SELECT "users".* >>>>> FROM "users" >>>>> And then gets the 6th element from the array of results. >>>>> >>>>> In reality, User.all[5] should be equivalent to: >>>>> User.limit(1).offset(5).first >>>>> in all circumstances that this addition to the query can be performed. >>>>> This means that someone looking for the nth User, for example, can >>>>> simply use the brackets as is idiomatic in Ruby, to perform the query >>>>> which >>>>> is truly desired by the user. >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Ruby on Rails: Core" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to rubyonrails-co...@**googlegroups**.com. >>>>> To post to this group, send email to rubyonra...@googlegroups.**com. >>>>> Visit this group at http://groups.google.com/**group** >>>>> /rubyonrails-core <http://groups.google.com/group/rubyonrails-core>. >>>>> For more options, visit >>>>> https://groups.google.com/**grou**ps/opt_out<https://groups.google.com/groups/opt_out> >>>>> . >>>>> >>>>> >>>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Ruby on Rails: Core" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to rubyonrails-co...@**googlegroups.com. >>> To post to this group, send email to rubyonra...@googlegroups.**com. >>> Visit this group at >>> http://groups.google.com/**group/rubyonrails-core<http://groups.google.com/group/rubyonrails-core> >>> . >>> For more options, visit >>> https://groups.google.com/**groups/opt_out<https://groups.google.com/groups/opt_out> >>> . >>> >>> >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/rubyonrails-core. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. 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