An expressive, opinionated ecosystem for building beautiful RESTful APIs with Ruby.
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README.md

Pragma

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Welcome to Pragma, an expressive, opinionated ecosystem for building beautiful RESTful APIs with Ruby.

You can think of this as a meta-gem that pulls in the following pieces:

Additionally, it also provides default CRUD operations that leverage all of the Pragma components and will make creating new resources in your API a breeze.

Looking for a Rails integration? Check out pragma-rails!

Philosophy

Pragma was created with a very specific goal in mind: to make the development of JSON APIs a matter of hours, not days. In other words, Pragma is for JSON APIs what Rails is for web applications.

Here are the ground rules:

  1. Pragma is opinionated. With Pragma, you don't get to make a lot of choices and that's exactly why people are using it: they want to focus on the business logic of their API rather than the useless details. We understand this approach will not work in some cases and that's alright. If you need more personalization, only use a subset of Pragma (see item 2) or something else.
  2. Pragma is modular. Pragma is built as a set of gems (currently 6), plus some standalone tools. You can pick one or more modules and use them in your application as you see fit. Even though they are completely independent from each other, they nicely integrate and work best when used together, creating an ecosystem that will dramatically speed up your design and development process.
  3. Pragma is designed to be Rails-free. Just as what happens with Trailblazer, our Rails integration is decoupled from the rest of the ecosystem and all of the gems can be used without Rails. This is just a byproduct of the project's design: Pragma is built with pure Ruby. pragma-rails is the only available framework integration at the moment, but more will come!

Why not Trailblazer?

Trailblazer and all of its companion projects are awesome. They are so awesome that Pragma is built on top of them: even though we're not using the Trailblazer gem itself yet, many of the Pragma gems are simply extensions of their Trailblazer counterparts:

Trailblazer and Pragma have different (but similar) places in the Ruby world: Trailblazer is an architecture for building all kinds of web applications in an intelligent, rational way, while Pragma is an architecture for building JSON APIs. We have shamelessly taken all of the flexibility and awesomeness from the Trailblazer project and restricted it to a narrow field of work, providing tools, helpers and integrations that could never be part of Trailblazer due to their specificity.

Thank you, guys!

Installation

Add this line to your application's Gemfile:

gem 'pragma'

And then execute:

$ bundle

Or install it yourself as:

$ gem install pragma

Usage

Project Structure

This gem works best if you follow the recommended structure for organizing resources:

└── api
    └── v1
        └── article
            ├── contract
            │   ├── create.rb
            │   └── update.rb
            ├── operation
            │   ├── create.rb
            │   ├── destroy.rb
            │   ├── index.rb
            │   └── update.rb
            └── decorator
            |   ├── collection.rb
            |   └── instance.rb
            └── policy.rb

Your modules and classes would, of course, follow the same structure: API::V1::Article::Policy and so on and so forth.

If you adhere to this structure, the gem will be able to locate all of your classes without any explicit configuration. This will save you a lot of time and is highly recommended.

Fantastic Five

Pragma comes with five built-in operations, often referred to as Fantastic Five (or "FF" for brevity). They are, of course, Index, Show, Create, Update and Destroy.

These operations leverage the full power of the integrated Pragma ecosystem and require all four components to be properly installed and configured in your application. You may reconfigure them to skip some of the steps, but it is highly recommended to use them as they come.

You can find these operations under lib/pragma/operation. To use them, simply create your own operations and inherit from ours. For instance:

module API
  module V1
    module Article
      module Operation
        class Create < Pragma::Operation::Create
          # This assumes that you have the following:
          #   1) an Article model
          #   2) a Policy (responding to #create?)
          #   3) a Create contract
          #   4) an Instance decorator
        end
      end
    end
  end
end

Macros

The FF are implemented through their own set of macros, which take care of stuff like authorizing, paginating, filtering etc.

If you want, you can use these macros in your own operations.

Classes

Used in: Index, Show, Create, Update, Destroy

The Classes macro is responsible of tying together all the Pragma components: put it into an operation and it will determine the class names of the related policy, model, decorators and contract. You can override any of these classes when defining the operation or at runtime if you wish.

Example usage:

module API
  module V1
    module Article
      module Operation
        class Create < Pragma::Operation::Base
          # Let the macro figure out class names.
          step Pragma::Macro::Classes()
          step :execute!
          
          # But override the contract.
          self['contract.default.class'] = Contract::CustomCreate
          
          def execute!(options)
            # `options` contains the following:
            #    
            #    `model.class`
            #    `policy.default.class`
            #    `policy.default.scope.class`
            #    `decorator.instance.class`
            #    `decorator.collection.class`
            #    `contract.default.class` 
            #    
            # These will be `nil` if the expected classes do not exist.
          end
        end
      end
    end
  end
end

Model

Used in: Index, Show, Create, Update, Destroy

The Model macro provides support for performing different operations with models. It can either build a new instance of the model, if you are creating a new record, for instance, or it can find an existing record by ID.

Example of building a new record:

module API
  module V1
    module Article
      module Operation
        class Create < Pragma::Operation::Base
          # This step can be done by Classes if you want.
          self['model.class'] = ::Article
           
          step Pragma::Macro::Model(:build)
          step :save!
          
          def save!(options)
            # Here you'd usually validate and assign parameters before saving.
  
            # ...
  
            options['model'].save!
          end
        end
      end
    end
  end
end

As we mentioned, Model can also be used to find a record by ID:

module API
  module V1
    module Article
      module Operation
        class Show < Pragma::Operation::Base
          # This step can be done by Classes if you want.
          self['model.class'] = ::Article
           
          step Pragma::Macro::Model(:find_by), fail_fast: true
          step :respond!
          
          def respond!(options)
            options['result.response'] = Response::Ok.new(
              entity: options['model']
            )
          end
        end
      end
    end
  end
end

In the example above, if the record is not found, the macro will respond with 404 Not Found and a descriptive error message for you. If you want to override the error handling logic, you can remove the fail_fast option and instead implement your own failure step.

Policy

Used in: Index, Show, Create, Update, Destroy

The Policy macro ensures that the current user can perform an operation on a given record.

Here's a usage example:

module API
  module V1
    module Article
      module Operation
        class Show < Pragma::Operation::Base
          # This step can be done by Classes if you want.
          self['policy.default.class'] = Policy
          
          step :model!
          step Pragma::Macro::Policy(), fail_fast: true
          # You can also specify a custom method to call on the policy:
          # step Pragma::Macro::Policy(action: :custom_method), fail_fast: true
          step :respond!
          
          def model!(params:, **)
            options['model'] = ::Article.find(params[:id])
          end
        end
      end
    end
  end
end

If the user is not authorized to perform the operation (i.e. if the policy's #show? method returns false), the macro will respond with 403 Forbidden and a descriptive error message. If you want to override the error handling logic, you can remove the fail_fast option and instead implement your own failure step.

The macro accepts the following options, which can be defined on the operation or at runtime:

  • policy.context: the context to use for the policy (optional, current_user is used if not provided).

Filtering

Used in: Index

The Filtering macro provides a simple interface to define basic filters for your API. You simply include the macro and configure which filters you want to expose to the users.

module API
  module V1
    module Article
      module Operation
        class Index < Pragma::Operation::Base
          step :model!
          step Pragma::Macro::Filtering()
          step :respond!

          self['filtering.filters'] = [
            Pragma::Filter::Equals.new(param: :by_category, column: :category_id),
            Pragma::Filter::Ilike.new(param: :by_title, column: :title)
          ]
          
          def model!(params:, **)
            options['model'] = ::Article.all
          end
        end
      end
    end
  end
end

With the example above, you are exposing the by_category filter and the by_title filters.

The following filters are available for ActiveRecord currently:

  • Equals: performs an equality (=) comparison (requires :column)-
  • Like: performs a LIKE comparison (requires :column).
  • Ilike: performs an ILIKE comparison (requires :column).
  • Where: adds a generic WHERE clause (requires :condition and passes the parameter's value as :value).
  • Scope: calls a method on the collection (requires :scope and passes the parameter's value as the first argument);
  • Boolean: calls a method on the collection (requires :scope and doesn't pass any arguments).

Support for more clauses as well as more ORMs will come soon.

Ordering

Used in: Index

As the name suggests, the Ordering macro allows you to easily implement default and user-defined ordering.

Here's an example:

module API
  module V1
    module Article
      module Operation
        class Index < Pragma::Operation::Base
          # This step can be done by Classes if you want.
          self['model.class'] = ::Article

          self['ordering.default_column'] = :published_at
          self['ordering.default_direction'] = :desc
          self['ordering.columns'] = %i[title published_at updated_at]

          step :model!

          # This will override `model` with the ordered relation.
          step Pragma::Macro::Ordering(), fail_fast: true

          step :respond!

          def model!(options)
            options['model'] = options['model.class'].all
          end
          
          def respond!(options)
            options['result.response'] = Response::Ok.new(
              entity: options['model']
            )
          end
        end
      end
    end
  end
end

If the user provides an invalid order column or direction, the macro will respond with 422 Unprocessable Entity and a descriptive error message. If you wish to implement your own error handling logic, you can remove the fail_fast option and implement your own failure step.

The macro accepts the following options, which can be defined on the operation or at runtime:

  • ordering.columns: an array of columns the user can order by.
  • ordering.default_column: the default column to order by (default: created_at).
  • ordering.default_direction: the default direction to order by (default: desc).
  • ordering.column_param: the name of the parameter which will contain the order column.
  • ordering.direction_param: the name of the parameter which will contain the order direction.

Pagination

Used in: Index

The Pagination macro is responsible for paginating collections of records through will_paginate. It also allows your users to set the number of records per page.

module API
  module V1
    module Article
      module Operation
        class Index < Pragma::Operation::Base
          # This step can be done by Classes if you want.
          self['model.class'] = ::Article

          step :model!

          # This will override `model` with the paginated relation.
          step Pragma::Macro::Pagination(), fail_fast: true

          step :respond!

          def model!(options)
            options['model'] = options['model.class'].all
          end
          
          def respond!(options)
            options['result.response'] = Response::Ok.new(
              entity: options['model']
            )
          end
        end
      end
    end
  end
end

In the example above, if the page or per-page number fail validation, the macro will respond with 422 Unprocessable Entity and a descriptive error message. If you wish to implement your own error handling logic, you can remove the fail_fast option and implement your own failure step.

The macro accepts the following options, which can be defined on the operation or at runtime:

  • pagination.page_param: the parameter that will contain the page number.
  • pagination.per_page_param: the parameter that will contain the number of items to include in each page.
  • pagination.default_per_page: the default number of items per page.
  • pagination.max_per_page: the max number of items per page.

This macro is best used in conjunction with the Collection and Pagination modules of Pragma::Decorator, which will expose all the pagination metadata.

Decorator

Used in: Index, Show, Create, Update

The Decorator macro uses one of your decorators to decorate the model. If you are using expansion, it will also make sure that the expansion parameter is valid.

Example usage:

module API
  module V1
    module Article
      module Operation
        class Show < Pragma::Operation::Base
          # This step can be done by Classes if you want.
          self['decorator.instance.class'] = Decorator::Instance
          
          step :model!
          step Pragma::Macro::Decorator(), fail_fast: true
          step :respond!
          
          def model!(params:, **)
            options['model'] = ::Article.find(params[:id])
          end
          
          def respond!(options)
            # Pragma does this for you in the default operations.
            options['result.response'] = Response::Ok.new(
              entity: options['result.decorator.instance']
            )
          end
        end
      end
    end
  end
end

The macro accepts the following options, which can be defined on the operation or at runtime:

  • expand.enabled: whether associations can be expanded.
  • expand.limit: how many associations can be expanded at once.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/pragmarb/pragma.

License

The gem is available as open source under the terms of the MIT License.