文件列表:

.rspec (26, 2020-03-12)
.travis.yml (475, 2020-03-12)
Gemfile (93, 2020-03-12)
Gemfile.lock (850, 2020-03-12)
LICENSE.txt (1070, 2020-03-12)
Rakefile (27, 2020-03-12)
changelog.md (935, 2020-03-12)
lib (0, 2020-03-12)
lib\waterfall.rb (2532, 2020-03-12)
lib\waterfall (0, 2020-03-12)
lib\waterfall\predicates (0, 2020-03-12)
lib\waterfall\predicates\base.rb (189, 2020-03-12)
lib\waterfall\predicates\chain.rb (1043, 2020-03-12)
lib\waterfall\predicates\on_dam.rb (234, 2020-03-12)
lib\waterfall\predicates\when_falsy.rb (132, 2020-03-12)
lib\waterfall\predicates\when_truthy.rb (323, 2020-03-12)
lib\waterfall\version.rb (41, 2020-03-12)
spec (0, 2020-03-12)
spec\chaining_services_spec.rb (2725, 2020-03-12)
spec\service_spec.rb (2445, 2020-03-12)
spec\spec_helper.rb (744, 2020-03-12)
spec\wf_object_spec.rb (5777, 2020-03-12)
waterfall.gemspec (1112, 2020-03-12)

[](https://codeclimate.com/github/apneadiving/waterfall) [](https://codeclimate.com/github/apneadiving/waterfall/coverage) [](https://travis-ci.org/apneadiving/waterfall) [](https://badge.fury.io/rb/waterfall) #### Goal Chain ruby commands, and treat them like a flow, which provides a new approach to application control flow. When logic is complicated, waterfalls show their true power and let you write intention revealing code. Above all they excel at chaining services. #### Material Upcoming book about failure management patterns, leveraging the gem: [The Unhappy path](https://leanpub.com/the-unhappy-path) General presentation blog post there: [Chain services objects like a boss](https://medium.com/p/chain-service-objects-like-a-boss-35d0b83606ab). Reach me [@apneadiving](https://twitter.com/apneadiving) #### Overview A waterfall object has its own flow of commands, you can chain your commands and if something wrong happens, you dam the flow which bypasses the rest of the commands. Here is a basic representation: - green, the flow goes on, `chain` by `chain` - red its bypassed and only `on_dam` blocks are executed.  #### Example ```ruby class FetchUser include Waterfall def initialize(user_id) @user_id = user_id end def call chain { @response = HTTParty.get("https://jsonplaceholder.typicode.com/users/#{@user_id}") } when_falsy { @response.success? } .dam { "Error status #{@response.code}" } chain(:user) { @response.body } end end ``` and call / chain: ```ruby Flow.new .chain(user1: :user) { FetchUser.new(1) } .chain(user2: :user) { FetchUser.new(2) } .chain {|outflow| puts(outflow.user1, outflow.user2) } # report success .on_dam {|error, context| puts(error, context) } # report error ``` Which works like:  ## Installation For installation, in your gemfile: gem 'waterfall' then `bundle` as usual. ## Waterfall mixin ### Outputs Each waterfall has its own `outflow` and `error_pool`. `outflow` is an Openstruct so you can get/set its property like a hash or like a standard object. ### Wiki Wiki contains many details, please check appropriate pages: - [Predicates](https://github.com/apneadiving/waterfall/wiki/Predicates) - [Wf Object](https://github.com/apneadiving/waterfall/wiki/Wf-object) - [Testing](https://github.com/apneadiving/waterfall/wiki/Testing) ### Koans (!) You can try and exercise your understanding of Waterfall using the [Koans here](https://github.com/apneadiving/waterfall_koans) ## Illustration of chaining Doing ```ruby Flow.new .chain(foo: :bar) { Flow.new.chain(:bar){ 1 } } ``` is the same as doing: ```ruby Flow.new .chain do |outflow, parent_waterfall| unless parent_waterfall.dammed? child = Wf.new.chain(:bar){ 1 } if child.dammed? parent_waterfall.dam(child.error_pool) else parent_waterfall.ouflow.foo = child.outflow.bar end end end ``` Hopefully you better get the chaining power this way. ## Syntactic sugar Given: ```ruby class MyWaterfall include Waterfall def call self.chain { 1 } end end ``` You may have noticed that I usually write: ```ruby Flow.new .chain { MyWaterfall.new } ``` instead of ```ruby Flow.new .chain { MyWaterfall.new.call } ``` Both are not really the same: - the only source of information for the gem is the return value of the block - if it returns a `Waterfall`, it will apply chaining logic. If ever the waterfall was not executed yet, it will trigger `call`, hence the convention. - if you call your waterfall object inside the block, the return value would be whatever your `call` method returns. So the gem doesnt know there was a waterfall involved and cannot apply chaining logic... unless you ensure `self` is always returned, which is cumbersome, so it's better to avoid this Syntax advice ========= ```ruby # this is valid self .chain { Service1.new } .chain { Service2.new } # this is equivalent self.chain { Service1.new } self.chain { Service2.new } # this is equivalent too chain { Service1.new } chain { Service2.new } # this is invalid Ruby due to the extra line self .chain { Service1.new } .chain { Service2.new } ``` Tips ========= ### Error pool For the error_pool, its up to you. But using Rails, I usually include ActiveModel::Validations in my services. Thus you: - have a standard way to deal with errors - can deal with multiple errors - support I18n out of the box - can use your model errors out of the box ### Conditional Flow In a service, there is one and single flow, so if you need conditionals to branch off, you can do: ```ruby self.chain { Service1.new } if foo? self.chain { Service2.new } else self.chain { Service3.new } end ``` ### Halting chain Sometimes you have a flow and you need a return value. You can use `halt_chain`, which is executed whether or not the flow is dammed. It returns what the block returns. As a consequence, it cannot be chained anymore, so it must be the last command: ```ruby self.halt_chain do |outflow, error_pool| if error_pool # what you want to return on error else # what you want to return from the outflow end end ``` ### Rails and transactions I'm used to wrap every single object involving database interactions within transactions, so it can be rolled back on error. Here is my usual setup: ```ruby module Waterfall extend ActiveSupport::Concern class Rollback < StandardError; end def with_transaction(&block) ActiveRecord::Base.transaction(requires_new: true) do yield on_dam do raise Waterfall::Rollback end end rescue Waterfall::Rollback self end end ``` And to use it: ```ruby class AuthenticateUser include Waterfall include ActiveModel::Validations validates :user, presence: true attr_reader :user def initialize(email, password) @email, @password = email, password end def call with_transaction do chain { @user = User.authenticate(@email, @password) } when_falsy { valid? } .dam { errors } chain(:user) { user } end end end ``` The huge benefit is that if you call services from services, everything will be rolled back. ### Undo If you get to dam a flow, this would trigger the `reverse_flow` method in all Services previously executed. `reverse_flow` is not executed on the service which just failed, consider the `on_dam` hook in this case. Take this as a hook to undo whatever you need to undo if things go wrong. Yet, you probably do not need to bother about databases inserts: this is the purpose of `with_transaction`. ### FYI `Flow` is just an alias for the `Wf` class, so just use the one you prefer :) Examples / Presentations ======================== - Check the [wiki for other examples](https://github.com/apneadiving/waterfall/wiki/Refactoring-examples). - [Structure and chain your POROs](http://slides.com/apneadiving/structure-and-chain-your-poros). - [Service objects implementations](https://slides.com/apneadiving/service-objects-waterfall-rails). - [Handling error in Rails](https://slides.com/apneadiving/handling-error-in-ruby-rails). Thanks ========= Huge thanks to [robhorrigan](https://github.com/robhorrigan) for the help during infinite naming brainstorming.

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