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ActiveHash is a simple base class that allows you to use a ruby hash as a readonly datasource for an ActiveRecord-like model.

ActiveHash assumes that every hash has an :id key, which is what you would probably store in a database. This allows you to seemlessly upgrade from ActiveHash objects to full ActiveRecord objects without having to change any code in your app, or any foreign keys in your database.

It also allows you to use #has_many and #belongs_to in your AR objects.

ActiveHash can also be useful to create simple test classes that run without a database - ideal for testing plugins or gems that rely on simple AR behavior, but don't want to deal with databases or migrations for the spec suite.

ActiveHash also ships with:

  • ActiveFile: a base class that you can use to create file data sources
  • ActiveYaml: a base class that will turn YAML into a hash and load the data into an ActiveHash object


Make sure is one of your gem sources, then run:

sudo gem install active_hash


To use ActiveHash, you need to:

  • Inherit from ActiveHash::Base
  • Define your data
  • Define your fields and/or default values

A quick example would be:

class Country < ActiveHash::Base = [
    {:id => 1, :name => "US"},
    {:id => 2, :name => "Canada"}

country = => "Mexico")  # => "Mexico" # => true

You can also use create:

class Country < ActiveHash::Base
  create :id => 1, :name => "US"
  create :id => 2, :name => "Canada"

If you are Pat Nakajima, you probably prefer add:

class Country < ActiveHash::Base
  add :id => 1, :name => "US"
  add :id => 2, :name => "Canada"

Auto-Defined fields

ActiveHash will auto-define all fields for you when you load the hash. For example, if you have the following class:

class CustomField < ActiveYaml::Base = [
    {:custom_field_1 => "foo"},
    {:custom_field_2 => "foo"},
    {:custom_field_3 => "foo"}

Once you call CustomField.all it will define methods for :custom_field_1, :custom_field_2 etc...

If you need the fields at load time, as opposed to after .all is called, you can also define them manually, like so:

class CustomField < ActiveYaml::Base
  fields :custom_field_1, :custom_field_2, :custom_field_3

NOTE: auto-defined fields will not override fields you've defined, either on the class or on the instance.

Defining Fields with default values

If some of your hash values contain nil, and you want to provide a default, you can specify defaults with the :field method:

class Country < ActiveHash::Base
  field   :is_axis_of_evil, :default => false

Defining Data

You can define data inside your class or outside. For example, you might have a class like this:

# app/models/country.rb
class Country < ActiveHash::Base

# config/initializers/data.rb = [
    {:id => 1, :name => "US"},
    {:id => 2, :name => "Canada"}

If you prefer to store your data in YAML, see below.

Class Methods

ActiveHash gives you ActiveRecord-esque methods like:

Country.all             # => returns all Country objects
Country.count           # => returns the length of the .data array
Country.first           # => returns the first country object
Country.last            # => returns the last country object
Country.find 1          # => returns the first country object with that id
Country.find [1,2]      # => returns all Country objects with ids in the array
Country.find :all       # => same as .all
Country.find :all, args # => the second argument is totally ignored, but allows it to play nicely with AR
Country.find_by_id 1    # => find the first object that matches the id

It also gives you a few dynamic finder methods. For example, if you defined :name as a field, you'd get:

Country.find_by_name "foo"                    # => returns the first object matching that name
Country.find_all_by_name "foo"                # => returns an array of the objects with matching names
Country.find_by_id_and_name 1, "Germany"      # => returns the first object matching that id and name
Country.find_all_by_id_and_name 1, "Germany"  # => returns an array of objects matching that name and id

Instance Methods

ActiveHash objects implement enough of the ActiveRecord api to satisfy most common needs. For example:

Country#id          # => returns the id or nil
Country#id=         # => sets the id attribute
Country#quoted_id   # => returns the numeric id
Country#to_param    # => returns the id as a string
Country#new_record? # => returns true if is not part of Country.all, false otherwise
Country#readonly?   # => true
Country#hash        # => the hash of the id (or the hash of nil)
Country#eql?        # => compares type and id, returns false if id is nil

ActiveHash also gives you methods related to the fields you defined. For example, if you defined :name as a field, you'd get:

Country#name        # => returns the passed in name
Country#name?       # => returns true if the name is not blank
Country#name=       # => sets the name

Saving in-memory records

The ActiveHash::Base.all method functions like an in-memory data store. You can save your records to the the .all array by using standard ActiveRecord create and save methods:

Country.all             # => []
Country.all             # [ <Country :id => 1> ]
country =
country.new_record?     # => true
country.new_record?     # => false
Country.all             # [ <Country :id => 1>, <Country :id => 2>  ]

Notice that when adding records to the collection, it will auto-increment the id for you by default. If you use string ids, it will not auto-increment the id. Available methods are:

Country.insert( record )

As such, ActiveHash::Base and its descendants should work with Fixjour or FactoryGirl, so you can treat ActiveHash records the same way you would any other ActiveRecord model in tests.

To clear all records from the in-memory array, call delete_all:

Country.delete_all  # => does not affect the yaml files in any way - just clears the in-memory array which can be useful for testing


You can create has_many and belongs_to associations to and from ActiveRecord. Out of the box, you can create .belongs_to associations from rails objects, like so:

class Country < ActiveHash::Base

class Person < ActiveRecord::Base
  belongs_to :country

ActiveHash will also work as a polymorphic parent:

class Country < ActiveHash::Base

class Person < ActiveRecord::Base
  belongs_to :location, :polymorphic => true

person =
person.location = Country.first
person.location # => Country.first

You can also use standard rails view helpers, like #collection_select:

<%= collection_select :person, :country_id, Country.all, :id, :name %>

If you include the ActiveHash::Associations module, you can also create associations from your ActiveHash classes, like so:

class Country < ActiveHash::Base
  include ActiveHash::Associations
  has_many :people

class Person < ActiveHash::Base
  include ActiveHash::Associations
  belongs_to :country
  has_many :pets

class Pet < ActiveRecord::Base

Once you define a belongs to, you also get the setter method:

class City < ActiveHash::Base
  include ActiveHash::Associations
  belongs_to :state

city =
city.state = State.first
city.state_id             # is

NOTE: You cannot use ActiveHash objects as children of ActiveRecord and I don't plan on adding support for that. It doesn't really make any sense, since you'd have to hard-code your database ids in your class or yaml files, which is a dependency inversion.

Also, the implementation of has_many and belongs_to is very simple - I hope to add better support for it later - it will only work in the trivial cases for now.

Thanks to baldwindavid for the ideas and code on that one.


If you want to store your data in YAML files, just inherit from ActiveYaml and specify your path information:

class Country < ActiveYaml::Base

By default, this class will look for a yml file named "countries.yml" in the same directory as the file. You can either change the directory it looks in, the filename it looks for, or both:

class Country < ActiveYaml::Base
  set_root_path "/u/data"
  set_filename "sample"

The above example will look for the file "/u/data/sample.yml".

Since ActiveYaml just creates a hash from the YAML file, you will have all fields specified in YAML auto-defined for you once you call all. You can format your YAML as an array, or as a hash:

# array style
- id: 1
  name: US
- id: 2
  name: Canada
- id: 3
  name: Mexico

# hash style
  id: 1
  name: US
  id: 2
  name: Canada
  id: 3
  name: Mexico


If you store encrypted data, or you'd like to store your flat files as CSV or XML or any other format, you can easily include ActiveHash to parse and load your file. Just add a custom ::load_file method, and define the extension you want the file to use:

class Country < ActiveFile::Base
  set_root_path "/u/data"
  set_filename "sample"

  class << self
    def extension

    def load_file

The two methods you need to implement are load_file, which needs to return an array of hashes, and .extension, which returns the file extension you are using. You have full_path available to you if you wish, or you can provide your own path.

Setting the default file location in Rails:

# config/initializers/active_file.rb
ActiveFile.set_root_path "config/activefiles"

In Rails, in development mode, it reloads the entire class, which reloads the file. In production, the data cached in memory.

NOTE: By default, .full_path refers to the current working directory. In a rails app, this will be RAILS_ROOT.


ActiveHash can expose its data in an Enumeration by setting constants for each record. This allows records to be accessed in code through a constant set in the ActiveHash class.

The field to be used as the constant is set using enum_accessor which takes the name of a field as an argument.

class Country < ActiveHash::Base
  include ActiveHash::Enum = [
      {:id => 1, :name => "US", :capital => "Washington, DC"},
      {:id => 2, :name => "Canada", :capital => "Ottawa"},
      {:id => 3, :name => "Mexico", :capital => "Mexico City"}
  enum_accessor :name

Records can be accessed by looking up the field constant:

=> "Washington DC"
=> 3
>> Country::CANADA
=> #<Country:0x10229fb28 @attributes={:name=>"Canada", :id=>2}

Constants are formed by first stripping all non-word characters and then upcasing the result. This means strings like "Blazing Saddles", "ReBar", "Mike & Ike" and "Ho! Ho! Ho!" become BLAZINGSADDLES, REBAR, MIKEIKE and HOHOHO.

The field specified as the enum_accessor must contain unique data values.


  • Jeff Dean
  • Mike Dalessio
  • Ben Woosley
  • John Pignata
  • Pat Nakajima
  • Brandon Keene
  • Dave Yeu
  • Brian Takita
  • Corey Innis
  • Peter Jaros
  • Michael Schubert


Copyright (c) 2009 Jeff Dean. See LICENSE for details.

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