Ruby on Rails是一个功能强大的WEB开发框架，在这里我们将会学到一些经常用到的Ruby on Rails内置方法，帮助大家熟练掌握其应用技巧。
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Ruby on Rails内置方法之对象是否为空blank?
puts [ ].blank? #=> true
puts { 1 => 2}.blank? #=> false
puts " cat ".blank? #=> false
puts "".blank? #=> true
puts " ".blank? #自动去除前后空格=> true
puts nil.blank? #=> true
Ruby on Rails内置方法之排序：group_by()
groups = posts.group_by {|post| post.author_id}
Ruby on Rails内置方法之组句：to_sentence()
puts [ "ant", "bat", "cat"].
to_sentence #=> "ant, bat, and cat"
puts [ "ant", "bat", "cat"].
to_sentence(:connector =>
"and not forgetting")
#=> "ant, bat, and not forgetting cat"
puts [ "ant", "bat", "cat"].
to_sentence(:skip_last_comma => true)
#=> "ant, bat and cat"
Ruby on Rails内置方法之分组：in_groups_of()
[1,2,3,4,5,6,7].in_groups_of(3)
{|slice| p slice}
#=> [1, 2, 3]
[4, 5, 6]
[7,nil, nil]
[1,2,3,4,5,6,7].in_groups
_of(3,"X") {|slice| p slice}
#=> [1, 2, 3]
[4, 5, 6]
[7,"X", "X"]
Ruby on Rails内置方法之字符串方法：
string = "Now is the time"
puts string.at(2) #=> "w"
puts string.from(8) #=> "he time"
puts string.to(8) #=> "Now is th"
puts string.first #=> "N"
puts string.first(3) #=> "Now"
puts string.last #=> "e"
puts string.last(4) #=> "time"
puts string.starts_with?("No") #=> true
puts string.ends_with?("ME") #=> false
count = Hash.new(0)
string.each_char {|ch| count[ch] += 1}
p count #=> {" "=>3, "w"=>1, "m"=>1,
"N"=>1, "o"=>1, "e"=>2, "h"=>1,
"s"=>1, "t"=>2, "i"=>2}