Ruby: How to turn a hash into HTTP parameters?

That is pretty easy with a plain hash like

{:a => "a", :b => "b"} 

which would translate into

"a=a&b=b"

But what do you do with something more complex like

{:a => "a", :b => ["c", "d", "e"]} 

which should translate into

"a=a&b[0]=c&b[1]=d&b[2]=e" 

Or even worse, (what to do) with something like:

{:a => "a", :b => [{:c => "c", :d => "d"}, {:e => "e", :f => "f"}]

Thanks for the much appreciated help with that!

For basic, non-nested hashes, Rails/ActiveSupport has 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

If you are using Ruby 1.9.2 or later, you can use URI.encode_www_form if you don't need arrays.

E.g. (from the Ruby docs in 1.9.3):

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"

You'll notice that array values are not set with key names containing [] like we've all become used to in query strings. The spec that encode_www_form uses is in accordance with the HTML5 definition of application/x-www-form-urlencoded data.

Update: This functionality was removed from the gem.

Julien, your self-answer is a good one, and I've shameless borrowed from it, but it doesn't properly escape reserved characters, and there are a few other edge cases where it breaks down.

require "addressable/uri"
uri = Addressable::URI.new
uri.query_values = {:a => "a", :b => ["c", "d", "e"]}
uri.query
# => "a=a&b[0]=c&b[1]=d&b[2]=e"
uri.query_values = {:a => "a", :b => [{:c => "c", :d => "d"}, {:e => "e", :f => "f"}]}
uri.query
# => "a=a&b[0][c]=c&b[0][d]=d&b[1][e]=e&b[1][f]=f"
uri.query_values = {:a => "a", :b => {:c => "c", :d => "d"}}
uri.query
# => "a=a&b[c]=c&b[d]=d"
uri.query_values = {:a => "a", :b => {:c => "c", :d => true}}
uri.query
# => "a=a&b[c]=c&b[d]"
uri.query_values = {:a => "a", :b => {:c => "c", :d => true}, :e => []}
uri.query
# => "a=a&b[c]=c&b[d]"

The gem is 'addressable'

gem install addressable

No need to load up the bloated ActiveSupport or roll your own, you can use Rack::Utils.build_query and Rack::Utils.build_nested_query. Here's a blog post that gives a good example:

require 'rack'

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

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

It even handles arrays:

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"]}

Or the more difficult nested stuff:

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"}]}

Here's a short and sweet one liner if you only need to support simple ASCII key/value query strings:

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"

Steal from Merb:

# File merb/core_ext/hash.rb, line 87
def to_params
  params = ''
  stack = []

  each do |k, v|
    if v.is_a?(Hash)
      stack << [k,v]
    else
      params << "#{k}=#{v}&"
    end
  end

  stack.each do |parent, hash|
    hash.each do |k, v|
      if v.is_a?(Hash)
        stack << ["#{parent}[#{k}]", v]
      else
        params << "#{parent}[#{k}]=#{v}&"
      end
    end
  end

  params.chop! # trailing &
  params
end

See http://noobkit.com/show/ruby/gems/development/merb/hash/to_params.html

class Hash
  def to_params
    params = ''
    stack = []

    each do |k, v|
      if v.is_a?(Hash)
        stack << [k,v]
      elsif v.is_a?(Array)
        stack << [k,Hash.from_array(v)]
      else
        params << "#{k}=#{v}&"
      end
    end

    stack.each do |parent, hash|
      hash.each do |k, v|
        if v.is_a?(Hash)
          stack << ["#{parent}[#{k}]", v]
        else
          params << "#{parent}[#{k}]=#{v}&"
        end
      end
    end

    params.chop! 
    params
  end

  def self.from_array(array = [])
    h = Hash.new
    array.size.times do |t|
      h[t] = array[t]
    end
    h
  end

end

{:a=>"a", :b=>"b", :c=>"c"}.map{ |x,v| "#{x}=#{v}" }.reduce{|x,v| "#{x}&#{v}" }

"a=a&b=b&c=c"

Here's another way. For simple queries.

I know this is an old question, but I just wanted to post this bit of code as I could not find a simple gem to do just this task for me.

module QueryParams

  def self.encode(value, key = nil)
    case value
    when Hash  then value.map { |k,v| encode(v, append_key(key,k)) }.join('&')
    when Array then value.map { |v| encode(v, "#{key}[]") }.join('&')
    when nil   then ''
    else            
      "#{key}=#{CGI.escape(value.to_s)}" 
    end
  end

  private

  def self.append_key(root_key, key)
    root_key.nil? ? key : "#{root_key}[#{key.to_s}]"
  end
end

Rolled up as gem here: https://github.com/simen/queryparams

The best approach it is to use Hash.to_params which is the one working fine with arrays.

{a: 1, b: [1,2,3]}.to_param
"a=1&b[]=1&b[]=2&b[]=3"

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"

If you are in the context of a Faraday request, you can also just pass the params hash as the second argument and faraday takes care of making proper param URL part out of it:

faraday_instance.get(url, params_hsh)

I like using this gem:

https://rubygems.org/gems/php_http_build_query

Sample usage:

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

2.6.3 :001 > hash = {:a => "a", :b => ["c", "d", "e"]}
=> {:a=>"a", :b=>["c", "d", "e"]}
2.6.3 :002 > hash.to_a.map { |x| "#{x[0]}=#{x[1].class == Array ? x[1].join(",") : x[1]}" 
}.join("&")
=> "a=a&b=c,d,e"