require 'uri'

class Hash
  def to_query_hash(key)
    reduce({}) do |h, (k, v)|
      new_key = key.nil? ? k : "#{key}[#{k}]"
      v = Hash[v.each_with_index.to_a.map(&:reverse)] if v.is_a?(Array)
      if v.is_a?(Hash)
        h.merge!(v.to_query_hash(new_key))
      else
        h[new_key] = v
      end
      h
    end
  end

  def to_query(key = nil)
    URI.encode_www_form(to_query_hash(key))
  end
end

2.4.2 :019 > {:a => "a", :b => "b"}.to_query_hash(nil)
 => {:a=>"a", :b=>"b"}

2.4.2 :020 > {:a => "a", :b => "b"}.to_query
 => "a=a&b=b"

2.4.2 :021 > {:a => "a", :b => ["c", "d", "e"]}.to_query_hash(nil)
 => {:a=>"a", "b[0]"=>"c", "b[1]"=>"d", "b[2]"=>"e"}

2.4.2 :022 > {:a => "a", :b => ["c", "d", "e"]}.to_query
 => "a=a&b%5B0%5D=c&b%5B1%5D=d&b%5B2%5D=e"

如果使用Ruby 1.9.2或更高版本，则可以使用URI。Encode_www_form如果你不需要数组。

例如(来自1.9.3的Ruby文档):

URI.encode_www_form([["q", "ruby"], ["lang", "en"]])
#=> "q=ruby&lang=en"
URI.encode_www_form("q" => "ruby", "lang" => "en")
#=> "q=ruby&lang=en"
URI.encode_www_form("q" => ["ruby", "perl"], "lang" => "en")
#=> "q=ruby&q=perl&lang=en"
URI.encode_www_form([["q", "ruby"], ["q", "perl"], ["lang", "en"]])
#=> "q=ruby&q=perl&lang=en"

您会注意到，数组值不是用包含[]的键名来设置的，就像我们在查询字符串中习惯的那样。encode_www_form使用的规范与HTML5对application/x-www-form-urlencoded data的定义一致。

如果你只需要支持简单的ASCII键/值查询字符串，这里有一个简短而甜蜜的语句:

hash = {"foo" => "bar", "fooz" => 123}
# => {"foo"=>"bar", "fooz"=>123}
query_string = hash.to_a.map { |x| "#{x[0]}=#{x[1]}" }.join("&")
# => "foo=bar&fooz=123"

对于基本的、非嵌套的散列，Rails/ActiveSupport有object# to_query。

>> {:a => "a", :b => ["c", "d", "e"]}.to_query
=> "a=a&b%5B%5D=c&b%5B%5D=d&b%5B%5D=e"
>> CGI.unescape({:a => "a", :b => ["c", "d", "e"]}.to_query)
=> "a=a&b[]=c&b[]=d&b[]=e"

http://api.rubyonrails.org/classes/Object.html#method-i-to_query

不需要加载臃肿的ActiveSupport或滚动自己的，您可以使用Rack::Utils。build_query和Rack::Utils.build_nested_query。这里有一篇博客文章给出了一个很好的例子:

require 'rack'

Rack::Utils.build_query(
  authorization_token: "foo",
  access_level: "moderator",
  previous: "index"
)

# => "authorization_token=foo&access_level=moderator&previous=index"

它甚至可以处理数组:

Rack::Utils.build_query( {:a => "a", :b => ["c", "d", "e"]} )
# => "a=a&b=c&b=d&b=e"
Rack::Utils.parse_query _
# => {"a"=>"a", "b"=>["c", "d", "e"]}

或者更难嵌套的东西:

Rack::Utils.build_nested_query( {:a => "a", :b => [{:c => "c", :d => "d"}, {:e => "e", :f => "f"}] } )
# => "a=a&b[][c]=c&b[][d]=d&b[][e]=e&b[][f]=f"
Rack::Utils.parse_nested_query _
# => {"a"=>"a", "b"=>[{"c"=>"c", "d"=>"d", "e"=>"e", "f"=>"f"}]}

我喜欢使用这个宝石:

https://rubygems.org/gems/php_http_build_query

示例用法:

puts PHP.http_build_query({"a"=>"b","c"=>"d","e"=>[{"hello"=>"world","bah"=>"black"},{"hello"=>"world","bah"=>"black"}]})

# a=b&c=d&e%5B0%5D%5Bbah%5D=black&e%5B0%5D%5Bhello%5D=world&e%5B1%5D%5Bbah%5D=black&e%5B1%5D%5Bhello%5D=world