DependencyManager

Dependency Manager using Dependency Injection wire together dependencies into a Service Container.

This tool may be unnecessary for dependency chains with only a few dependencies, but if you find yourself dealing with 20 or more dependencies you need to wire together this will quickly become very useful.

Dependency Manager uses Factories to assemble dependencies, and uses the arguments of initialize to figure out what depends on what, and finally what order all the dependencies should be loaded in.

Consider this example factory:

class FlagsFactory < DependencyManager::Factory
  # ...

  def initialize(logger:, timing:, hype_person: nil, **dependencies)
    super(**dependencies)

    @logger = logger
    @timing = timing
    @hype_person = hype_person
  end

  # ...
end

This factory would depend on a LoggerFactory and TimingFactory, and have an optional dependency on a HypePerson factory. The remaining **dependencies relate to the base DependencyManager factory which we'll get into in a moment.

It should be noted that there are no particularly quick starts to using this library. It is suggested to read over the entire Overview and Usage. Quick References will be created soon.

Overview and Usage

DependencyManager uses a few core concepts:

• DependencyTree - TSort-based system for ordering dependencies by what depends on what.
• Factory - Builds dependencies from configuration and validates them.
• Resolver - Resolves dependencies needed for each Factory.
• Container - Builds and stores the artifacts of each finished Factory.

Users will only directly interact with the Factory and the Container, while DependencyTree and Resolver will help wire everything together behind the scenes. We'll be focusing on the two public interfaces.

Factories

A Factory seeks to fulfill a few goals:

• Filtering - A Factory may be disabled, causing it to not build.
• Configure - Defines and extracts configuration for dependencies.
• Validate - Validates that configuration using Dry::Schema.
• Loading - Loads external dependencies like gems via require.
• Dependency Chains - Finds dependencies necessary to "build" a factory.
• Build - Builds the dependency based on the above content.

Factory Filtering

Factories can be enabled or disabled through the enabled? method, which defaults to false in the Factory class which children inherit from:

class MyFactory < DependencyManager::Factory
  # ...

  def enabled?
    configuration[:enabled] == true
  end

  # ...
end

Just defining this method, however, will not do much unless you remember to put it in your build step:

class MyFactory < DependencyManager::Factory
  # ...

  def build
    return unless enabled?

    # ...
  end

  def enabled?
    configuration[:enabled] == true
  end

  # ...
end

...which will cause it to not be injected into downstream Factory builds.

Factory Configuration

Factories are configured via an injected Hash from the Container, and a user determined app_context:

# /lib/dependency_manager/factory.rb
def initialize(app_context: nil, factory_config:)
  @app_context = app_context
  @factory_config = factory_config
end

The application context is typically a class containing information like environment, name, and other meta-information. This is defaulted to nil to represent an optional dependency.

The factory_config is derived from the name of the Factory:

# /lib/dependency_manager/container.rb
private def get_config(klass)
  @configuration.fetch(klass.dependency_name, {})
end

...which is automatically provided from the Factorys class name. For instance, LoggerFactory would have a dependency name of logger, and would feed the logger values from the following configuration passed to a container:

# /spec/dependency_manager/container_spec.rb
{
  logger:      { enabled: true, level: :info },
  flags:       { enabled: true, default_values: { a: 1, b: 2, c: 3 } },
  timing:      { enabled: true },
  hype_person: { enabled: true }
}

In your own Factorys there are two configuration methods to keep in mind: configuration and default_configuration:

# Inline definition

# Config stanza:
#   { a: 3, b: 4 }

class MyFactory < DependencyManager::Factory
  # Depends on logger, forwards `app_context` and `configuration` on to the parent class
  def initialize(logger:, **dependencies)
    super(**dependencies)
    @logger = logger
  end

  # Would return: { a: 3, b: 4, c: 3 }
  def configuration
    # Default implementation, use `super()` here to get this config
    # if you want to do more configuration. Caching is used by default as well.
    @configuration ||= deep_merge(default_configuration, @factory_config)
  end

  # Reasonable defaults for the class, defaulting to `{}` unless specified
  def default_configuration
    { a: 1, b: 2, c: 3 }
  end
end

Configurations are typically used in the build phase of a Factory.

As with other methods it's not necessary unless you need it, and build will not automiatically call it.

Factory Validation

An optional, but recommended step, to validate configurations:

# /spec/support/dependency_factories/flags_factory.rb
class FlagsFactory < DependencyManager::Factory
  validate_with do
    required(:enabled).filled(:bool)
    required(:default_values).hash
  end

  # ...
end

This will validate configuration by using Dry::Schema validations via the validate! (error raising) and validate (result returning) methods.

It's recommended to run this in the build step of your Factory right after checking if it's enabled:

# /spec/support/dependency_factories/flags_factory.rb
class FlagsFactory < DependencyManager::Factory
  validate_with do
    required(:enabled).filled(:bool)
    required(:default_values).hash
  end

  # ...

  def build
    return unless enabled?

    validate!

    # ...
  end

  # ...
end

As with other methods it's not necessary unless you need it, and build will not automiatically call it.

Factory Loading

Some Factorys, if not most, are created to load gems that you don't own into your Service Container ecosystem. load_requirements is how DependencyManager handles that issue:

# /spec/support/dependency_factories/flags_factory.rb
class FlagsFactory < DependencyManager::Factory
  # ...

  def build
    return unless enabled?

    validate!

    load_dependencies

    # ...
  end

  def load_dependencies
    require 'flags'
  end

  # ...
end

As with other methods it's not necessary unless you need it, and build will not automiatically call it.

Factory Dependency Chains

Dependency chains are the main reason this library exists. In a Service Container dependencies rely on each other, often times in hard to manage orders. DependencyManager solves this using the arguments to the initialize function on each Factory to find dependencies:

def initialize(logger:, other:, optional: nil)

In this case there are required dependencies on :logger and :other, but an optional dependency on :optional. These work via required kwargs and optional kwargs, and nil isn't the only value that can be used there, in fact more sane defaults are a better idea where possible.

These names correspond to, and require the presence of factories named LoggerFactory, OtherFactory, and OptionalFactory. Without them the program will crash and warn you of this:

# spec/dependency_manager/factory_spec.rb > .get > When the factory does not exist
"Tried to get non-existant Factory. Did you remember to define it?: InvalidFactory"

Missing resources in general will attempt to raise informative errors to let you know what might have gone wrong.

Factory Builds

The final step of a factory is to actually build it and get the dependency back out the other side, and all together it'll look a bit something like this:

# /spec/dependency_manager/container_spec.rb
#
# Flag configuration stanza:
{ enabled: true, default_values: { a: 1, b: 2, c: 3 } },

# /spec/support/dependency_factories/flags_factory.rb
class FlagsFactory < DependencyManager::Factory
  validate_with do
    required(:enabled).filled(:bool)
    required(:default_values).hash
  end

  def initialize(logger:, timing:, hype_person: nil, **dependencies)
    super(**dependencies)

    @logger = logger
    @timing = timing
    @hype_person = hype_person
  end

  def build
    return unless enabled?

    validate!

    load_requirements

    Flags.new(
      logger: @logger,
      timing: @timing,
      default_values: configuration[:default_values],
      hype_person: @hype_person
    )
  end

  def load_requirements
    require 'flags'
  end

  def enabled?
    configuration[:enabled] == true
  end
end

In general the order for a build function should be:

• Is it on?
• Is it valid?
• What do we need to load to make it work?
• Get configuration ready
• Build it!

This factory has no configuration step defined, but uses the automatically built configuration to get :default_values.

Once built by the Container it will be registered and fed to other dependencies executing later that require what it produces, which brings us to Container next.

Containers

A Container is what brings all the Factorys together to produce the dependencies you need to run your application.

It aims to do a few things:

• Capture Configuration - Container takes pre-read configuration in the format Hash[Symbol, Any]
• Load Factories - Load all the Factorys
• Load Dependency Tree - Call out to DependencyTree and find out what needs to be built
• Order Dependencies - Based on dependencies, use tsort to order dependencies from DependencyTree.
• Resolve Dependencies - Resolve requirements from Factory based on what's already been built, if any are required.
• Build Factory - Build the Factory and wire it back into dependencies for downstream Factorys to potentially use.
• Present Dependencies - Once they're done, give back dependencies to use how you see fit.

Container Configuration

Container will not load configuration, but instead takes it directly in the form of a Hash[Symbol, Any]:

# Modified from: /spec/dependency_manager/container_spec.rb

AppContext = Struct.new(:name, :env)

container = DependencyManager::Container.new(
  app_context:   AppContext.new('README', 'test'),
  configuration: {
    logger:      { enabled: true, level: :info },
    flags:       { enabled: true, default_values: { a: 1, b: 2, c: 3 } },
    timing:      { enabled: true },
    hype_person: { enabled: true }
  },
  factories: DependencyManager::Factory.factories
)

container.build

container.fetch(:logger)
# => instance_of Logger

Typically this would come from a YAML or JSON file, but can be manually entered as well.

An AppContext can be any class, but is typically useful for changing behavior based on application-level configuration like what environment the script is currently running on and using different configs if it's in sandbox vs production. This option is not necessary, but recommended for more complicated applications.

Container Loading Factories

The factories option for creating a new Container defaults to Factory.factories, which contains all classes inheriting from DependencyManager::Factory. If this behavior is not wanted an Array of Factorys can be passed in instead:

# Modified from: /spec/dependency_manager/container_spec.rb
factories: DependencyManager::Factory.factories

# ...or manually
factories: [LoggerFactory, FlagsFactory, HypePersonFactory]

When using the manual route one can also use register to add a new Factory before the Container is built:

container = DependencyManager::Container.new(...)
container.register(HypePersonFactory)

...but as this uses a Set behind the scenes it will not allow a Factory to be loaded more than once.

Container Loading Dependency Tree

Container uses DependencyTree to figure out what depends on what. Using a basic example:

# /spec/dependency_manager/dependency_tree_spec.rb
tree = DependencyManager::DependencyTree.new(
  a: [:b, :c],
  b: [:c],
  c: []
)

a depends on b and c, b depends on c, and c depends on nothing. Remembering back above, Factorys implement a method for finding what other Factorys they depend on using the arguments to initialize via factory_dependencies:

# /lib/dependency_manager/factory.rb > Singleton methods

def parameters
  instance_method(:initialize).parameters
end

def dependencies
  dependencies = parameters
    .select { |type, _name| KEYWORD_ARGS.include?(type) }
    .map(&:last)

  dependencies - CONTEXT_DEPENDENCIES
end

def factory_dependencies
  dependencies.map { |d| "#{d}_factory".to_sym }
end

So our above hypothetical initialize method:

def initialize(logger:, other:, optional: nil)

...would give us the following dependency chain:

[:logger_factory, :other_factory, :optional_factory]

It also has additional methods of required_dependencies and optional_dependencies to figude out what's actually needed to build it successfully. All of this comes for free based on arguments to initialize of each Factory.

Container Ordering Dependencies

Given these TSort, which is included in DependencyTree, can figure out what order to load dependencies in. Taking a look at our above:

# /spec/dependency_manager/dependency_tree_spec.rb
tree = DependencyManager::DependencyTree.new(
  a: [:b, :c],
  b: [:c],
  c: []
)

tree.tsort
# => [:c, :b, :a]

It would run c then b then a, which makes sense as c has no other dependencies.

TSort is also kind enough to keep us from creating cycles by accident:

# /spec/dependency_manager/dependency_tree_spec.rb
tree = DependencyManager::DependencyTree.new(
  a: [:b, :c],
  b: [:c],
  c: [:b] # LOOP
)

tree.tsort
# raises TSort::Cyclic

Container Resolving Dependencies

# /lib/dependency_manager/container.rb
resolved_dependencies = Resolver.new(
  factory: factory,
  loaded_dependencies: dependencies
).resolve

As each dependency is built it will look into the already built dependencies for dependencies it needs. If c is built first, dependencies will already have a reference to it for b when it comes up to be built, and so forth for a.

/spec/dependency_manager/resolver_spec.rb contains examples of this behavior, but for now know that it relies on order to cascade dependencies where they need to go when they need to be there.

Container Building Dependencies

Once we have the dependencies we can inject hte rest of the information we need, and we now have a factory ready to be built:

# /lib/dependency_manager/container.rb
factory_instance = factory.new(
  app_context:    @app_context,
  factory_config: get_config(factory),
  **resolved_dependencies
)

...once ready we turn around and build it:

# /lib/dependency_manager/container.rb
@dependencies[factory.dependency_name] = factory_instance.build

Factorys have dependency_name which gives back a snake-cased version of just the dependency name, such that LoggerFactory becomes logger, which is what other Factorys expect. We map that name to the produced artifact, and that artifact is now available to all Factorys that build after it.

This is the reason for TSort is to figure out what that order is. Note this may not be necessary in cases where your dependencies do not have to be actively loaded, and something like Dry::Container may be a better idea in those cases.

Container Presenting Dependencies

Once that's done all of the dependencies have been created and you can get them out in a few ways:

# Modified from: /spec/dependency_manager/container_spec.rb

AppContext = Struct.new(:name, :env)

container = DependencyManager::Container.new(
  app_context:   AppContext.new('README', 'test'),
  configuration: {
    logger:      { enabled: true, level: :info },
    flags:       { enabled: true, default_values: { a: 1, b: 2, c: 3 } },
    timing:      { enabled: true },
    hype_person: { enabled: true }
  },
  factories: DependencyManager::Factory.factories
)

container.build
# All dependencies returned here too, but prefer to use the next two methods

container.fetch(:logger)
# => instance_of Logger

container.to_h
# {
#   logger:      instance_of Logger,
#   flags:       instance_of Flags,
#   timing:      instance_of Timing,
#   hype_person: instance_of HypePerson
# }

...and with that you now have a Container to work with, whether that be tying into Rails or whatever other framework you're needing to.

Installation

Add this line to your application's Gemfile:

gem 'dependency_manager'

And then execute:

$ bundle

Or install it yourself as:

$ gem install dependency_manager

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. 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.

Contributing

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

License

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

Code of Conduct

Everyone interacting in the DependencyManager project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.