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Her

Build Status

Her is an ORM (Object Relational Mapper) that maps REST resources to Ruby objects. It is designed to build applications that are powered by a RESTful API and no database.

Installation

In your Gemfile, add:

gem "her"

That’s it!

Usage

First, you have to define which API your models will be bound to. For example, with Rails, you would create a new config/initializers/her.rb file with this line:

# config/initializers/her.rb
Her::API.setup :base_uri => "https://api.example.com"

And then to add the ORM behavior to a class, you just have to include Her::Model in it:

class User
  include Her::Model
end

After that, using Her is very similar to many ActiveModel-like ORMs:

User.all
# GET https://api.example.com/users and return an array of User objects

User.find(1)
# GET https://api.example.com/users/1 and return a User object

@user = User.create(:fullname => "Tobias Fünke")
# POST "https://api.example.com/users" with the data and return a User object

@user = User.new(:fullname => "Tobias Fünke")
@user.occupation = "actor"
@user.save
# POST https://api.example.com/users with the data and return a User object

@user = User.find(1)
@user.fullname = "Lindsay Fünke"
@user.save
# PUT https://api.example.com/users/1 with the data and return+update the User object

Parsing data

By default, Her handles JSON data. It expects the data to be formatted in a certain structure. The default is this:

// The response of GET /users/1
{
  "data" : {
    "id" : 1,
    "name" : "Tobias Fünke"
  }
}

// The response of GET /users
{
  "data" : [
    {
      "id" : 1,
      "name" : "Tobias Fünke"
    },
    {
      "id" : 2,
      "name" : "Lindsay Fünke"
    }
  ],
  "metadata" : {
    "page" : 1,
    "per_page" : 10
  }
}

However, you can define your own parsing method, using a Faraday response middleware. The middleware is expected to return a hash with three keys: data, errors and metadata. The following code enables parsing JSON data and treating this data as first-level properties:

class MyCustomParser < Faraday::Response::Middleware
  def on_complete(env)
    json = JSON.parse(env[:body], :symbolize_names => true)
    errors = json.delete(:errors) || []
    metadata = json.delete(:metadata) || []
    env[:body] = {
      :data => json,
      :errors => errors,
      :metadata => metadata,
    }
  end
end
Her::API.setup :base_uri => "https://api.example.com", :middleware => [MyCustomParser] + Her::API.default_middleware
end

# User.find(1) will now expect "https://api.example.com/users/1" to return something like '{ "id": 1, "name": "Tobias Fünke" }'

Relationships

You can define has_many, has_one and belongs_to relationships in your models. The relationship data is handled in two different ways. When parsing a resource from JSON data, if there’s a relationship data included, it will be used to create new Ruby objects.

If no relationship data was included when parsing a resource, calling a method with the same name as the relationship will fetch the data (providing there’s an HTTP request available for it in the API).

For example, with this setup:

class User
  include Her::Model
  has_many :comments
  has_one :role
  belongs_to :organization
end

class Comment
  include Her::Model
end

class Role
  include Her::Model
end

class Organization
  include Her::Model
end

If there’s relationship data in the resource, no extra HTTP request is made when calling the #comments method and an array of resources are returned:

@user = User.find(1) # { :data => { :id => 1, :name => "George Michael Bluth", :comments => [{ :id => 1, :text => "Foo" }, { :id => 2, :text => "Bar" }], :role => { :id => 1, :name => "Admin" }, :organization => { :id => 2, :name => "Bluth Company" } }}
@user.comments # => [#<Comment id=1>, #<Comment id=2>] fetched directly from @user
@user.role # => #<Role id=1> fetched directly from @user
@user.organization # => #<Organization id=2> fetched directly from @user

If there’s no relationship data in the resource, an extra HTTP request (to GET /users/1/comments) is made when calling the #comments method:

@user = User.find(1) # { :data => { :id => 1, :name => "George Michael Bluth" }}
@user.comments # => [#<Comment id=1>, #<Comment id=2>] fetched from /users/1/comments

For has_one relationship, an extra HTTP request (to GET /users/1/role) is made when calling the #role method:

@user = User.find(1) # { :data => { :id => 1, :name => "George Michael Bluth" }}
@user.role # => #<Role id=1> fetched from /users/1/role

For belongs_to relationship, an extra HTTP request (to GET /organizations/2) is made when calling the #organization method:

@user = User.find(1) # { :data => { :id => 1, :name => "George Michael Bluth", :organization_id => 2 }}
@user.organization # => #<Organization id=2> fetched from /organizations/2

However, subsequent calls to #comments or #role will not trigger the extra HTTP request.

Hooks

You can add before and after hooks to your models that are triggered on specific actions (save, update, create, destroy):

class User
  include Her::Model
  before_save :set_internal_id

  def set_internal_id
    self.internal_id = 42 # Will be passed in the HTTP request
  end
end

@user = User.create(:fullname => "Tobias Fünke")
# POST /users&fullname=Tobias+Fünke&internal_id=42

In the future, adding hooks to all models will be possible, as well as defining and triggering your own hooks (eg. for your custom requests).

Custom requests

You can easily add custom methods for your models. You can either use get_collection (which maps the returned data to a collection of resources), get_resource (which maps the returned data to a single resource) or get_raw (which yields the parsed data return from the HTTP request). Other HTTP methods are supported (post_raw, put_resource, etc.)

class User
  include Her::Model

  def self.popular
    get_collection("/users/popular")
  end

  def self.total
    get_raw("/users/stats") do |parsed_data|
      parsed_data[:data][:total_users]
    end
  end
end

User.popular  # => [#<User id=1>, #<User id=2>]
User.total    # => 42

Multiple APIs

It is possible to use different APIs for different models. Instead of calling Her::API.setup, you can create instances of Her::API:

# config/initializers/her.rb
$my_api = Her::API.new
$my_api.setup :base_uri => "https://my_api.example.com"

$other_api = Her::API.new
$other_api.setup :base_uri => "https://other_api.example.com"

You can then define which API a model will use:

class User
  include Her::Model
  uses_api $my_api
end

class Category
  include Her::Model
  uses_api $other_api
end

User.all
# GET https://my_api.example.com/users

Category.all
# GET https://other_api.example.com/categories

Things to be done

  • Support for Faraday middleware to handle caching, alternative formats, etc.
  • Hooks before save, update, create, destroy, etc.
  • Better error handling
  • Better introspection for debug
  • Better documentation

Contributors

Feel free to contribute and submit issues/pull requests on GitHub.

Take a look at the spec folder before you do, and make sure bundle exec rake spec passes after your modifications :)

License

Her is © 2012 Rémi Prévost and may be freely distributed under the LITL license. See the LICENSE file.

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