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And after you ve isolated a single Article object, you can get at its attributes: >> articles[0].title => "RailsConf" What s happening here is that all produces an array, and you access the object at the 0 index and call the title method. You can also use the first method, which all arrays respond to, and get the same result, but with a little more natural syntax: >> articles.first.title => "RailsConf" If you want to iterate over the collection, you can use the each method, which, again, works with all arrays. Here, you loop over the array, extract each item into a variable called article, and print its title attribute using the puts command: >> articles.each {|article| puts article.title} RailsConf Introduction to SQL Introduction to Active Record RubyConf 2010 Rails Pub Nite => [#<Article id: 1,..> #<Article id: 2,..>, #<Article id: 3,..>, #<Article id: 4,..> , #<Article id: 5,..>] Sometimes, you want your results ordered. For example, if you re listing all your articles, you probably want them listed chronologically. To do so, you can use the order method, which accepts as argument the name of the column or columns. For you SQL heroes, it corresponds to the SQL ORDER clause: >> articles = Article.order("published_at") => [#<Article id: 1,..> #<Article id: 2,..>, #<Article id: 3,..>, #<Article id: 4,..> , #<Article id: 5,..>] >> articles.each {|article| puts article.published_at } 2010-02-27 00:00:00 UTC 2010-05-01 04:00:00 UTC 2010-05-01 04:00:00 UTC 2010-05-19 00:00:00 UTC 2010-05-19 00:00:00 UTC => [#<Article id: 1,..> #<Article id: 2,..>, #<Article id: 3,..>, #<Article id: 4,..> , #<Article id: 5,..>] Notice that when you call the order method, it returns an array object as you may have expected. One thing that happens on the background is that Active Record allows you to chain calls to multiple methods before sending the command to the database; so you can call all, followed by order, and some other methods we ll talk about in the next chapter, to create more precise database queries. Also, Active Record is smart enough to use lazy loading, a practice that only hits the database when necessary in this example, when you call the each method. By default, any column is ordered in ascending order (for example, 1 10, or a z). If you want to reverse this to get descending order, use the DESC modifier (the same way you do in SQL, because the value of order parameter is really just a SQL fragment):
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>> articles = Article.order ('published_at DESC') => [#<Article id: 4,..> #<Article id: 5,..>, #<Article id: 2,..>, #<Article id: 3,..> , #<Article id: 1,..>] >> articles.each {|article| puts article.published_at } 2010-05-19 00:00:00 UTC 2010-05-19 00:00:00 UTC 2010-05-01 04:00:00 UTC 2010-05-01 04:00:00 UTC 2010-02-27 00:00:00 UTC => [#<Article id: 4,..> #<Article id: 5,..>, #<Article id: 2,..>, #<Article id: 3,..> , #<Article id: 1,..>]
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Although finding a record by its primary key is useful, it requires that you know the id to begin with, which isn t always the case. Sometimes you want to find records based on other criteria. This is where conditions come into play. Conditions correspond to the SQL WHERE clause. If you want to find a record by its title, you call the where method and pass a value that contains either a hash of conditions or a SQL fragment. Here, you use a hash of conditions to indicate you want the first article with the title RailsConf: >> Article.where(:title => 'RailsConf').first => #<Article id: 1, title: "RailsConf", body: "RailsConf is the official gathering for Rails devel...", published_at: "2010-02-27 00:00:00", created_at: "2010-05-01 23:12:09", updated_at: "2010-05-01 23:12:09", excerpt: nil, location: nil> Because you use first, you get only one record (the first one in the result set, even if there is more than one result). If you instead use all, you get back a collection, even if the collection has only one item in it: >> Article.where(:title => 'RailsConf').all => [#<Article id: 1, title: "RailsConf", body: "RailsConf is the official gathering for Rails devel...", published_at: "2010-02-27 00:00:00", created_at: "2010-05-01 23:12:09", updated_at: "2010-05-01 23:12:09", excerpt: nil, location: nil>] Notice the square brackets, and remember that they indicate an array. More often than not, when you re doing a all operation, you expect more than one record in return. But all always produces an array, even if that array is empty: >> Article.where(:title => 'Unknown').all => []
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