Sinject

Welcome to Sinject! a simple dependency injection framework for ruby.

[Note: The update to v1.0.0 contains breaking changes. All code has now been moved into the module Sinject::* and the register method of the container has been modified to take an options hash as opposed to requiring multiple method arguments.]

Add this line to your application's Gemfile:

gem 'sinject'

And then execute:

$ bundle

Or install it yourself as:

$ gem install sinject

Registering dependencies

Dependency objects need to be registered with the container before use, to do so you need to configure the Sinject::Container. [Note: This should be done after all code files have been required as the last step before your application starts.]

#initialize the container
container = Sinject::Container.new

#register your dependencies
container.register({ :key => :cache_store, :class => RedisCacheStore, :singleton => true })
container.register({ :key => :country_repository, :class => MySqlCountryRepository, :singleton => false })

Dependencies can be registered with the container in 2 modes:

• Single instance: This mode ensures that only 1 instance is created for the registered dependency and that all requests to the container for that dependency return the same instance.
• Multi instance: This mode ensures that a new instance of the registered dependency is returned for each request received by the container.

The registration mode can be set by specifying true or false to the :singleton argument of the containers register method.

Dependencies that require custom initialization can be registered with an initialization block to handle the creation of the dependency, this allows you more control over how the dependency is created if required:

container.register({ :key => :cache_store, :class => RedisCacheStore, :singleton => true }) do
    instance = RedisCacheStore.new
    instance.host = 'http://localhost'
    instance.port = '6369'
    instance
end

Dependencies with a custom initialization block must return an object of the registered dependency class type, if an unexpected instance is returned then Sinject will raise a Sinject::DependencyInitializeException.

Assigning dependencies

To assign a dependency to an object you need to add the dependency attribute to the class and specify the symbol key that was used to register the dependency with the SinjectContainer:

class MySqlCountryRepository

    dependency :cache_store

	.....
end

class CountryController < ActionController::Base

	dependency :country_repository

	.....
end

Sinject will then inject the registered dependency to that object and it will be accessible via the dependency key:

country_controller.country_repository.cache_store

Dependency Contracts

Dependency contracts can be defined to validate registered dependencies are valid for the task they are being registered for. (If you are familiar with other type based languages then you can think of this as a kind of Interface)

To create a dependency contract you need to create a new class with empty methods for each of the methods that the dependency needs to respond to in order to fulfill it's role:

class LoggerContract
    def write(message)
    end
end

Then when registering a dependency for the role the contract is written for, you can assign the contract:

#register the dependency
container.register({ :key => :logger, :class => FileLogger, :singleton => false, :contract => LoggerContract })

Sinject will then validate that the registered dependency meets the requirements specified within the contract. If a dependency does not meet the contract requirements then 1 of the following exceptions will be raised:

• Sinject::DependencyContractMissingMethodsException is raised when 1 or more methods from the contract could not be found on the dependency.
• Sinject::DependencyContractInvalidParametersException is raised when the parameters of a contract method do not match the parameters found on a dependency method.

Dependency Groups

Dependency registration groups can be created to allow groups of dependencies to be set without the need for manual registration (e.g. to include with a gem for auto registration), or to allow different dependency groups to be loaded in different circumstances (e.g. per environment).

To create a dependency group, create a class that inherits from the Sinject::DependencyGroup base class and implement the register & is_valid? methods.

For example:

#create a development only dependency group
class DevelopmentDependencies < Sinject::DependencyGroup
    def register(container)
        container.register(:cache_store, LocalCacheStore, true)
        container.register(:logger, TerminalLogger, true)
    end

    def valid?
        Rails.env.development?
    end
end

To load valid dependency groups the following method needs to be called from the container:

container.load_groups

After checking out the repo, run bin/setup to install dependencies. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/sage/sinject. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

This gem is available as open source under the terms of the MIT licence.

Copyright (c) 2018 Sage Group Plc. All rights reserved.