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Hashie is a growing collection of tools that extend Hashes and make them more useful.


Hashie is available as a RubyGem:

$ gem install hashie


You're reading the documentation for the stable release of Hashie, 3.2.0. Please read UPGRADING when upgrading from a previous version.

Hash Extensions

The library is broken up into a number of atomically includeable Hash extension modules as described below. This provides maximum flexibility for users to mix and match functionality while maintaining feature parity with earlier versions of Hashie.

Any of the extensions listed below can be mixed into a class by include-ing Hashie::Extensions::ExtensionName.


Coercions allow you to set up "coercion rules" based either on the key or the value type to massage data as it's being inserted into the Hash. Key coercions might be used, for example, in lightweight data modeling applications such as an API client:

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :user, User

user_hash = { name: "Bob" }
Tweet.new(user: user_hash)
# => automatically calls User.coerce(user_hash) or
#    User.new(user_hash) if that isn't present.

Value coercions, on the other hand, will coerce values based on the type of the value being inserted. This is useful if you are trying to build a Hash-like class that is self-propagating.

class SpecialHash < Hash
  include Hashie::Extensions::Coercion
  coerce_value Hash, SpecialHash

  def initialize(hash = {})
    hash.each_pair do |k,v|
      self[k] = v

Coercing Collections

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :mentions, Array[User]
  coerce_key :friends, Set[User]

user_hash = { name: "Bob" }
mentions_hash= [user_hash, user_hash]
friends_hash = [user_hash]
tweet = Tweet.new(mentions: mentions_hash, friends: friends_hash)
# => automatically calls User.coerce(user_hash) or
#    User.new(user_hash) if that isn't present on each element of the array

tweet.mentions.map(&:class) # => [User, User]
tweet.friends.class # => Set

Coercing Hashes

class Relation
  def initialize(string)
    @relation = string

class Tweet < Hash
  include Hashie::Extensions::Coercion
  coerce_key :relations, Hash[User => Relation]

user_hash = { name: "Bob" }
relations_hash= { user_hash => "father", user_hash => "friend" }
tweet = Tweet.new(relations: relations_hash)
tweet.relations.map { |k,v| [k.class, v.class] } # => [[User, Relation], [User, Relation]]
tweet.relations.class # => Hash

# => automatically calls User.coerce(user_hash) on each key
#    and Relation.new on each value since Relation doesn't define the `coerce` class method


The KeyConversion extension gives you the convenience methods of symbolize_keys and stringify_keys along with their bang counterparts. You can also include just stringify or just symbolize with Hashie::Extensions::StringifyKeys or Hashie::Extensions::SymbolizeKeys.


The MergeInitializer extension simply makes it possible to initialize a Hash subclass with another Hash, giving you a quick short-hand.


The MethodAccess extension allows you to quickly build method-based reading, writing, and querying into your Hash descendant. It can also be included as individual modules, i.e. Hashie::Extensions::MethodReader, Hashie::Extensions::MethodWriter and Hashie::Extensions::MethodQuery.

class MyHash < Hash
  include Hashie::Extensions::MethodAccess

h = MyHash.new
h.abc = 'def'
h.abc  # => 'def'
h.abc? # => true


This extension can be mixed in to instantly give you indifferent access to your Hash subclass. This works just like the params hash in Rails and other frameworks where whether you provide symbols or strings to access keys, you will get the same results.

A unique feature of Hashie's IndifferentAccess mixin is that it will inject itself recursively into subhashes without reinitializing the hash in question. This means you can safely merge together indifferent and non-indifferent hashes arbitrarily deeply without worrying about whether you'll be able to hash[:other][:another] properly.


This extension can be mixed in to silently ignore undeclared properties on initialization instead of raising an error. This is useful when using a Trash to capture a subset of a larger hash.

class Person < Trash
  include Hashie::Extensions::IgnoreUndeclared
  property :first_name
  property :last_name

user_data = {
  first_name: 'Freddy',
  last_name: 'Nostrils',
  email: '[email protected]'

p = Person.new(user_data) # 'email' is silently ignored

p.first_name # => 'Freddy'
p.last_name  # => 'Nostrils'
p.email      # => NoMethodError


This extension allow you to easily include a recursive merging system to any Hash descendant:

class MyHash < Hash
  include Hashie::Extensions::DeepMerge

h1 = MyHash.new
h2 = MyHash.new

h1 = { x: { y: [4,5,6] }, z: [7,8,9] }
h2 = { x: { y: [7,8,9] }, z: "xyz" }

h1.deep_merge(h2) # => { x: { y: [7, 8, 9] }, z: "xyz" }
h2.deep_merge(h1) # => { x: { y: [4, 5, 6] }, z: [7, 8, 9] }


This extension can be mixed in to provide for safe and concise retrieval of deeply nested hash values. In the event that the requested key does not exist a block can be provided and its value will be returned.

Though this is a hash extension, it conveniently allows for arrays to be present in the nested structure. This feature makes the extension particularly useful for working with JSON API responses.

user = {
  name: { first: 'Bob', last: 'Boberts' },
  groups: [
    { name: 'Rubyists' },
    { name: 'Open source enthusiasts' }

user.extend Hashie::Extensions::DeepFetch

user.deep_fetch :name, :first # => 'Bob'
user.deep_fetch :name, :middle # => 'KeyError: Could not fetch middle'

# using a default block
user.deep_fetch :name, :middle { |key| 'default' }  # =>  'default'

# a nested array
user.deep_fetch :groups, 1, :name # => 'Open source enthusiasts'


Mash is an extended Hash that gives simple pseudo-object functionality that can be built from hashes and easily extended. It is designed to be used in RESTful API libraries to provide easy object-like access to JSON and XML parsed hashes.


mash = Hashie::Mash.new
mash.name? # => false
mash.name # => nil
mash.name = "My Mash"
mash.name # => "My Mash"
mash.name? # => true
mash.inspect # => <Hashie::Mash name="My Mash">

mash = Hashie::Mash.new
# use bang methods for multi-level assignment
mash.author!.name = "Michael Bleigh"
mash.author # => <Hashie::Mash name="Michael Bleigh">

mash = Hashie::Mash.new
# use under-bang methods for multi-level testing
mash.author_.name? # => false
mash.inspect # => <Hashie::Mash>

Note: The ? method will return false if a key has been set to false or nil. In order to check if a key has been set at all, use the mash.key?('some_key') method instead.


Dash is an extended Hash that has a discrete set of defined properties and only those properties may be set on the hash. Additionally, you can set defaults for each property. You can also flag a property as required. Required properties will raise an exception if unset.


class Person < Hashie::Dash
  property :name, required: true
  property :email
  property :occupation, default: 'Rubyist'

p = Person.new # => ArgumentError: The property 'name' is required for this Dash.

p = Person.new(name: "Bob")
p.name # => 'Bob'
p.name = nil # => ArgumentError: The property 'name' is required for this Dash.
p.email = '[email protected]'
p.occupation   # => 'Rubyist'
p.email        # => '[email protected]'
p[:awesome]    # => NoMethodError
p[:occupation] # => 'Rubyist'
p.update_attributes!(name: 'Trudy', occupation: 'Evil')
p.occupation   # => 'Evil'
p.name         # => 'Trudy'
p.update_attributes!(occupation: nil)
p.occupation   # => 'Rubyist'

Properties defined as symbols are not the same thing as properties defined as strings.


class Tricky < Hashie::Dash
  property :trick
  property 'trick'

p = Tricky.new(trick: 'one', 'trick' => 'two')
p.trick # => 'one', always symbol version
p[:trick] # => 'one'
p['trick'] # => 'two'

Note that accessing a property as a method always uses the symbol version.

class Tricky < Hashie::Dash
  property 'trick'

p = Tricky.new('trick' => 'two')
p.trick # => NoMethodError

Mash and Rails 4 Strong Parameters

To enable compatibility with Rails 4 use the hashie_rails gem.


A Trash is a Dash that allows you to translate keys on initialization. It is used like so:

class Person < Hashie::Trash
  property :first_name, from: :firstName

This will automatically translate the firstName key to first_name when it is initialized using a hash such as through:

Person.new(firstName: 'Bob')

Trash also supports translations using lambda, this could be useful when dealing with external API's. You can use it in this way:

class Result < Hashie::Trash
  property :id, transform_with: lambda { |v| v.to_i }
  property :created_at, from: :creation_date, with: lambda { |v| Time.parse(v) }

this will produce the following

result = Result.new(id: '123', creation_date: '2012-03-30 17:23:28')
result.id.class         # => Fixnum
result.created_at.class # => Time


Clash is a Chainable Lazy Hash that allows you to easily construct complex hashes using method notation chaining. This will allow you to use a more action-oriented approach to building options hashes.

Essentially, a Clash is a generalized way to provide much of the same kind of "chainability" that libraries like Arel or Rails 2.x's named_scopes provide.


c = Hashie::Clash.new
c.where(abc: 'def').order(:created_at)
c # => { where: { abc: 'def' }, order: :created_at }

# You can also use bang notation to chain into sub-hashes,
# jumping back up the chain with _end!
c = Hashie::Clash.new
c # => { where: { abc: 'def', ghi: 123 }, order: :created_at }

# Multiple hashes are merged automatically
c = Hashie::Clash.new
c.where(abc: 'def').where(hgi: 123)
c # => { where: { abc: 'def', hgi: 123 } }


Rash is a Hash whose keys can be Regexps or Ranges, which will map many input keys to a value.

A good use case for the Rash is an URL router for a web framework, where URLs need to be mapped to actions; the Rash's keys match URL patterns, while the values call the action which handles the URL.

If the Rash's value is a proc, the proc will be automatically called with the regexp's MatchData (matched groups) as a block argument.


# Mapping names to appropriate greetings
greeting = Hashie::Rash.new( /^Mr./ => "Hello sir!", /^Mrs./ => "Evening, madame." )
greeting["Mr. Steve Austin"] # => "Hello sir!"
greeting["Mrs. Steve Austin"] # => "Evening, madame."

# Mapping statements to saucy retorts
mapper = Hashie::Rash.new(
  /I like (.+)/ => proc { |m| "Who DOESN'T like #{m[1]}?!" },
  /Get off my (.+)!/ => proc { |m| "Forget your #{m[1]}, old man!" }
mapper["I like traffic lights"] # => "Who DOESN'T like traffic lights?!"
mapper["Get off my lawn!"]      # => "Forget your lawn, old man!"


Note: The Rash is automatically optimized every 500 accesses (which means that it sorts the list of Regexps, putting the most frequently matched ones at the beginning).

If this value is too low or too high for your needs, you can tune it by setting: rash.optimize_every = n.




Copyright (c) 2009-2014 Intridea, Inc. (http://intridea.com/) and contributors.

MIT License. See LICENSE for details.