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Smooth JSON APIs
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Smooth provides a way of developing JSON APIs on top of SQL Databases that is, well, smooth.

Smooth provides a ruby library and a front end graphical application that make the process of developing APIs for your web and mobile applications really productive.

General idea: in the abstract

A resource is, generally, a database backed collection of models. A resource can be accessed by users who have different roles and relations to the data. A resource is accessed in one of two ways: queries, and commands. The resource can be presented in different views.

The benefits of a declarative, data driven programming style

As a developer you get API interface inspection capabilities for free by coding your API in the smooth style. These capabilities can give you a lot of power for your every day development practice.

Generating documentation, generating custom querying and reporting tools, generating API client libraries, generating automated test code, and a number of other tasks become much much easier.

The Smooth approach starts with declarations

In smooth we develop resources by describing or declaring data about the different functions an API client will need access to to provide its users the means of interacting with their data that they need.


Commands handle API requests whose intent is to change data in the resource. A user updating their profile. A person adding a new recipe to their cookbook. A moderator removing a rude comment on their blog.

We define the set of commands available and what information they require:

resource "Books" do
  desc "Update a book's attributes"
  command :update do
    # Will ensure the command is run with
    # Book.accessible_to(current_user).find(id).
    scope :accessible_to

    params do
      duck :id, :method => :to_s

      optional do
        desc "the title of the book"
        string :title


The DSL for commands allows us to document and code the interface to define:

  • In what ways can a user change the data?
  • What specific parameters must an API client pass to these commands?
  • Describe what they mean for a developer?
  • What type of data, what values?

API clients often have large sets of data that they need to reduce to a
manageable size to render in some view in their application or dynamic page on their website.

  query do
    # calls `Book.accessible_to(current_user)`
    scope :accessible_to

    params do
      desc "The year the book was published (example: YYYY)"
      integer :year_published, operator: :gte

      desc "A partial string to filter the title by"
      string :title, operator: :like

    role :admin do
      scope :all

The Query DSL lets us document and decide:

  • In what ways can a user or role filter the data?
  • Specifically what parameters would an API client pass?
  • What type of data, what values?
  • Should a user only be allowed to see a hard coded subset of records?

Given a query which returns a set of zero or more records, we will often want to present this data in an optimized format. We'll want to convert a specific timestamp into a description of the amount of time that has passed. We'll want to display individual things in a table, or maybe as a pie chart.

  desc "The default serializer for book"
  serializer do
    desc "A unique id for the book", :type => :integer
    attribute :id

    desc "The title of the book", :type => :string
    attribute :title

    desc "The author of the book"
    has_one :author

    desc "Documentation for computed property"
    def computed_property

    desc "Another way for doing computed properties"
    computed(:another_computed_property) do

In smooth's serializer DSL we document and decide:

  • In what ways would an API client want to see this data?
  • As individual objects? As a reduced / aggregated report?
  • In what ways does the data change depending on who is looking at it?
  • Are there different serializers for different roles?
  • What are each of the attributes and what do they mean?

Coding the smooth way

Using the Smooth API toolkit is possible:

  • Use it in your rails application, edit the different classes of ruby objects whose file names, locations, and class names follow a familiar naming convention.

  • Use it in a standalone ruby application as a rack compatible application or middleware. File organization and class naming approach follows same familiar naming conventions.

  • Use the DSL to build an entire application from one or more configuration files organized however you want.

  • Use the smooth developer mode to build the structure of your API and resources visually and from a user interface. Customize small methods with configuration, and if necessary, custom code.

  • Use the smooth developer mode and don't write any code at all. (Obviously you are limited in what you can do with this approach, but for simple apps this is often effective.)

Example Code

# Sample App Structure (Rails or Standalone)

- app
  - models
    - book.rb
  - commands
    - create_book.rb
    - update_book.rb
  - queries
    - book_query.rb
  - serializers
    - book_serializer.rb
    - book_summary_serializer.rb


class BookQuery < Smooth::Query
  params do
    desc "Filter the books by a wildcard title"
    string :title_is_like, operator: "like"

    desc "Filter the books published after a certain year"
    integer :published_after_year, operator: "greater_than_or_equal_to", min_length: 4

Run the query: #=> Book: ActiveRecord::Relation

Inspect the query interface:


    "title_is_like": {
      description: "Filter the books by wildcard title" 

TODO: Command Example

TODO: Serializers Example

TODO: Router Example

TODO: Backbone + Ember Data Model Generator

TODO: Interactive API Documentation Generator

TODO: Objective-C CoreData Configuration Generator


Add this line to your application's Gemfile:

gem 'smooth'

And then execute:

$ bundle

Or install it yourself as:

$ gem install smooth


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request
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