# Find\_by\_ always uses sql? **URL:** \ **Category:** Rails\ **Created:** [August 15, 2007, 11:58pm UTC](https://www.ruby-forum.com/t/find-by-always-uses-sql/112161 "2007-08-15T23:58:38Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![ldk2005](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/d9b06d/32.png) [@ldk2005](https://www.ruby-forum.com/u/ldk2005)\ **Post date:** [August 15, 2007, 11:58pm UTC](https://www.ruby-forum.com/t/find-by-always-uses-sql/112161/1 "2007-08-15T23:58:38Z")
Hi, If I eagerly load a collection during the initial find, do scoped find\_by\_ calls later _always_ use sql? What is the best pattern to use to not do another db trip? Is there some specialized rails method to handle this case? eg Author has\_many :books larry = Author.find\_by\_name(‘larry’, :include =\> :books) ruby = larry.books.find\_by\_title(‘Ruby’) # does this ALWAYS do a db call? # Is the following the best way to get the one (or nil) book? temp = larry.books.select{|book| book.title == ‘ruby’} ruby = temp.size == 1 ? temp[0] : nil Thank you for your comments and time, Larry ---
**Author:** ![ldk2005](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/d9b06d/32.png) [@ldk2005](https://www.ruby-forum.com/u/ldk2005)\ **Post date:** [August 17, 2007, 11:56am UTC](https://www.ruby-forum.com/t/find-by-always-uses-sql/112161/2 "2007-08-17T11:56:29Z")
Larry K. wrote: > If I eagerly load a collection during the initial find, do scoped > find\_by\_ calls later _always_ use sql? Yes. > call? > > # Is the following the best way to get the one (or nil) book? > > temp = larry.books.select{|book| book.title == ‘ruby’} > ruby = temp.size == 1 ? temp[0] : nil Yes. Or ruby = larry.books.detect {|book| book.title == ‘ruby’} – We develop, watch us RoR, in numbers too big to ignore. ---
**Author:** ![ldk2005](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/d9b06d/32.png) [@ldk2005](https://www.ruby-forum.com/u/ldk2005)\ **Post date:** [August 20, 2007, 6:32am UTC](https://www.ruby-forum.com/t/find-by-always-uses-sql/112161/3 "2007-08-20T06:32:34Z")
Larry K. wrote: > Hi, > > If I eagerly load a collection during the initial find, do scoped > find\_by\_ calls later _always_ use sql? > > What is the best pattern to use to not do another db trip? > Is there some specialized rails method to handle this case? > > eg > Author > has\_many :books > > larry = Author.find\_by\_name(‘larry’, :include =\> :books) > > ruby = larry.books.find\_by\_title(‘Ruby’) # does this ALWAYS do a db > call? > > # Is the following the best way to get the one (or nil) book? > > temp = larry.books.select{|book| book.title == ‘ruby’} > ruby = temp.size == 1 ? temp[0] : nil > > Thank you for your comments and time, > > Larry Sense you now have all Larry’s books in memory it is probably better to search through the memory using ruby calls like: ruby = larry.books.detect {|book| book.title == ‘ruby’} On the other hand ruby is a comparatively slow next most database engines. If you have a large number of books by Larry (or authors in general) AND you know you only need to find a small finite set of them (like one) The database may be faster then the Ruby script interrupter at doing what it does best – finding a subset of items in a table. Eager loading is best used when you know you will need all or most of the related information in another table, (eg All the books Larry wrote) or information in a related table for every member of the first. (eg, the best selling book for each Author) ---
**Author:** ![ldk2005](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/d9b06d/32.png) [@ldk2005](https://www.ruby-forum.com/u/ldk2005)\ **Post date:** [August 17, 2007, 11:45pm UTC](https://www.ruby-forum.com/t/find-by-always-uses-sql/112161/4 "2007-08-17T23:45:10Z")
Hi Mark, Thanks for your time, much appreciated. > Yes. Or ruby = larry.books.detect {|book| book.title == ‘ruby’} Regards, Larry ---
**Author:** ![ldk2005](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/d9b06d/32.png) [@ldk2005](https://www.ruby-forum.com/u/ldk2005)\ **Post date:** [August 20, 2007, 2:05pm UTC](https://www.ruby-forum.com/t/find-by-always-uses-sql/112161/5 "2007-08-20T14:05:44Z")
Hi – On Mon, 20 Aug 2007, John M. wrote: > > temp = larry.books.select{|book| book.title == ‘ruby’} > > ruby = temp.size == 1 ? temp[0] : nil > > > > Thank you for your comments and time, > > > > Larry > > Sense you now have all Larry’s books in memory it is probably better to > search through the memory using ruby calls like: > > ruby = larry.books.detect {|book| book.title == ‘ruby’} find and find\_by\_\* on a collection are smart, though: they get rolled into one database query with the collection query itself. For example: $ ./script/console Loading development environment. > > f = Food.find(:first) > > =\> #\“bread”, “id”=\>“1”, > > “food\_group\_id”=\>“2”}\> > > f.ingredients.find\_by\_description(“flour”) > > =\> #\“3”, > > “description”=\>“flour”, “food\_id”=\>“1”}\> Here’s the query log: Food Load (0.000726) SELECT \* FROM foods LIMIT 1 Ingredient Load (0.000394) SELECT \* FROM ingredients WHERE (ingredients.food\_id = 1) AND (ingredients.“description” = ‘flour’) LIMIT 1 Notice how the second select combines two where clauses, so the whole collection isn’t loaded into memory. The find\_by\_\* methods have some overhead, though, since they have to pass through method\_missing. You can also do: f.ingredients.find(:first, :conditions =\> “description = ‘flour’”) which won’t have that overhead. Of course, find\_by\_\* is nice and concise, so it’s OK for cases where you’re not looking to tweak performance. David – - Books: RAILS ROUTING (new! [http://www.awprofessional.com/title/0321509242](http://www.awprofessional.com/title/0321509242)) RUBY FOR RAILS ([Ruby for Rails](http://www.manning.com/black)) - Ruby/Rails training & consulting: Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com))