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https://github.com/bkuhlmann/transactable

A domain specific language for functionally composable transactional workflows.
https://github.com/bkuhlmann/transactable

function-composition transaction

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A domain specific language for functionally composable transactional workflows.

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README 

        
:toc: macro

:toclevels: 5

:figure-caption!:



:command_pattern_link: link:https://alchemists.io/articles/command_pattern[Command Pattern]

:debug_link: link:https://github.com/ruby/debug[Debug]

:dry_container_link: link:https://dry-rb.org/gems/dry-container[Dry Container]

:dry_events_link: link:https://dry-rb.org/gems/dry-events[Dry Events]

:dry_monads_link: link:https://dry-rb.org/gems/dry-monads[Dry Monads]

:dry_schema_link: link:https://dry-rb.org/gems/dry-schema[Dry Schema]

:dry_validation_link: link:https://dry-rb.org/gems/dry-validation[Dry Validation]

:function_composition_link: link:https://alchemists.io/articles/ruby_function_composition[Function Composition]

:infusible_link: link:https://alchemists.io/projects/infusible[Infusible]

:railway_pattern_link: link:https://fsharpforfunandprofit.com/posts/recipe-part2[Railway Pattern]



= Transactable



⚠ī¸ *This gem is deprecated and will be fully destroyed on 2025-03-05. Please use the link:https://alchemists.io/projects/pipeable[Pipeable] gem instead.* ⚠ī¸



A DSL for transactional workflows built atop native {function_composition_link} which leverages the {railway_pattern_link}. This allows you to write a sequence of _steps_ that cleanly read from left-to-right or top-to-bottom which results in a success or a failure without having to rely on exceptions which are expensive.



toc::[]



== Features



* Built atop of native {function_composition_link}.

* Adheres to the {railway_pattern_link}.

* Provides built-in and customizable domain-specific steps.

* Provides chainable _pipes_ which can be used to build more complex workflows.

* Supports instrumentation for tracking metrics, logging usage, and much more.

* Compatible with {dry_monads_link}.

* Compatible with {infusible_link}.



== Requirements



. link:https://www.ruby-lang.org[Ruby].

. A strong understanding of {function_composition_link}.



== Setup



To install _with_ security, run:



[source,bash]

----

# 💡 Skip this line if you already have the public certificate installed.

gem cert --add <(curl --compressed --location https://alchemists.io/gems.pem)

gem install transactable --trust-policy HighSecurity

----



To install _without_ security, run:



[source,bash]

----

gem install transactable

----



You can also add the gem directly to your project:



[source,bash]

----

bundle add transactable

----



Once the gem is installed, you only need to require it:



[source,ruby]

----

require "transactable"

----



== Usage



You can turn any object into a _transaction_ by requiring and including this gem as follows:



[source,ruby]

----

require "csv"

require "transactable"



class Demo

  include Transactable



  def initialize client: CSV

    @client = client

  end



  def call data

    pipe data,

         check(/Book.+Price/, :match?),

         :parse,

         map { |item| "#{item[:book]}: #{item[:price]}" }

  end



  private



  attr_reader :client



  def parse result

    result.fmap do |data|

      client.instance(data, headers: true, header_converters: proc { |key| key.downcase.to_sym })

            .to_a

            .map(&:to_h)

    end

  end

end

----



The above allows `Demo#call` to be a _transactional_ sequence steps which may pass or fail due to all step being {dry_monads_link}. This is the essence of the {railway_pattern_link}.



To execute the above example, you'd only need to pass CSV content to it:



[source,ruby]

----

Demo.new.call <<~CSV

  Book,Author,Price,At

  Mystics,urGoh,10.50,2022-01-01

  Skeksis,skekSil,20.75,2022-02-13

CSV

----



The computed result is a success with each book listing a price:



....

Success ["Mystics: 10.50", "Skeksis: 20.75"]

....



=== Pipe



Once you've included the `Transactable` module within your class, the `#pipe` method is available to you and is how you build a sequence of steps for processing. The method signature is:



[source,ruby]

----

pipe(input, *steps)

----



The first argument is your input which can be a Ruby primitive or a monad. Regardless, the input will be automatically wrapped as a `Success` -- but only if not a `Result` to begin with -- before passing to the first step. From there, all steps are _required_ to answer a monad in order to adhere to the {railway_pattern_link}.



Behind the scenes, the `#pipe` method is syntactic sugar on top of {function_composition_link} which means if this code were to be rewritten:



[source,ruby]

----

pipe csv,

     check(/Book.+Price/, :match?),

     :parse,

     map { |item| "#{item[:book]}: #{item[:price]}" }

----



Then the above would look like this using native Ruby:



[source,ruby]

----

(

  check(/Book.+Price/, :match?) >>

  method(:parse) >>

  map { |item| "#{item[:book]}: #{item[:price]}" }

).call Success(csv)

----



The problem with native function composition is that it reads backwards by passing your input at the end of all sequential steps. With the `#pipe` method, you have the benefit of allowing your eye to read the code from top to bottom in addition to not having to type multiple _forward composition_ operators.



=== Steps



There are several ways to compose steps for your transactional pipe. As long as all steps succeed, you'll get a successful response. Otherwise, the first step to fail will pass the failure down by skipping all subsequent steps (unless you dynamically attempt to turn the failure into a success). The following sections detail how to mix and match steps for building a robust implementation.



==== Basic



The following are the basic (default) steps for building for more advanced functionality.



===== As



Allows you to message the input as different output. Example:



[source,ruby]

----

pipe :a, as(:inspect)                  # Success ":a"

pipe %i[a b c], as(:dig, 1)            # Success :b

pipe Failure("Danger!"), as(:inspect)  # Failure "Danger!"

----



===== Bind



Allows you to perform operations on a successful result only. You are then responsible for answering a success or failure accordingly. This is a convenience wrapper to native {dry_monads_link} `#bind` functionality. Example:



[source,ruby]

----

pipe %i[a b c], bind { |input| Success input.join("-") }           # Success "a-b-c"

pipe %i[a b c], bind { |input| Failure input }                     # Failure [:a, :b, :c]

pipe Failure("Danger!"), bind { |input| Success input.join("-") }  # Failure "Danger!"

----



===== Check



Allows you to check if the input and messaged object evaluate to `true` or `Success`. When successful, input is passed through as a `Success`. When false, input is passed through as a `Failure`. Example:



[source,ruby]

----

pipe :a, check(%i[a b], :include?)                  # Success :a

pipe :a, check(%i[b c], :include?)                  # Failure :a

pipe Failure("Danger!"), check(%i[a b], :include?)  # Failure "Danger!"

----



===== Fmap



Allows you to unwrap a successful operation, make a modification, and rewrap the modification as a new success. This is a convenience wrapper to native {dry_monads_link} `#fmap` functionality. Example:



[source,ruby]

----

pipe %i[a b c], fmap { |input| input.join "-" }           # Success "a-b-c"

pipe Failure("Danger!"), fmap { |input| input.join "-" }  # Failure "Danger!"

----



===== Insert



Allows you to insert an element after the input (default behavior) and wraps native link:https://rubyapi.org/o/array#method-i-insert[Array#insert] functionality. If the input is not an array, it will be cast as one. You can use the `:at` key to specify where you want insertion to happen. This step is most useful when needing to assemble arguments for passing to a subsequent step. Example:



[source,ruby]

----

pipe :a, insert(:b)                  # Success [:a, :b]

pipe :a, insert(:b, at: 0)           # Success [:b, :a]

pipe %i[a c], insert(:b, at: 1)      # Success [:a, :b, :c]

pipe Failure("Danger!"), insert(:b)  # Failure "Danger!"

----



===== Map



Allows you to map over an enumerable and wraps native link:https://rubyapi.org/o/enumerable#method-i-map[Enumerable#map] functionality.



[source,ruby]

----

pipe %i[a b c], map(&:inspect)           # Success [":a", ":b", ":c"]

pipe Failure("Danger!"), map(&:inspect)  # Failure "Danger!"

----



===== Merge



Allows you to merge the input with additional attributes as a single hash. If the input is not a hash, then the input will be merged with the attributes using `step` as the key. The default `step` key can be renamed to a different key by using the `:as` key. Like the _Insert_ step, this is most useful when needing to assemble arguments and/or data for consumption by subsequent steps. Example:



[source,ruby]

----

pipe({a: 1}, merge(b: 2))             # Success {a: 1, b: 2}

pipe "test", merge(b: 2)              # Success {step: "test", b: 2}

pipe "test", merge(as: :a, b: 2)      # Success {a: "test", b: 2}

pipe Failure("Danger!"), merge(b: 2)  # Failure "Danger!"

----



===== Orr



Allows you to operate on a failure and produce either a success or another failure. This is a convenience wrapper to native {dry_monads_link} `#or` functionality.



ℹī¸ Syntactically, `or` can't be used for this step since `or` is a native Ruby keyword so `orr` is used instead.



Example:



[source,ruby]

----

pipe %i[a b c], orr { |input| Success input.join("-") }          # Success [:a, :b, :c]

pipe Failure("Danger!"), orr { Success "Resolved" }              # Success "Resolved"

pipe Failure("Danger!"), orr { |input| Failure "Big #{input}" }  # Failure "Big Danger!"

----



===== Tee



Allows you to run an operation and ignore the response while input is passed through as output. This behavior is similar in nature to the link:https://www.gnu.org/savannah-checkouts/gnu/gawk/manual/html_node/Tee-Program.html[tee] program in Bash. Example:



[source,ruby]

----

pipe "test", tee(Kernel, :puts, "Example.")



# Example.

# Success "test"



pipe Failure("Danger!"), tee(Kernel, :puts, "Example.")



# Example.

# Failure "Danger!"

----



===== To



Allows you to delegate to an object -- which doesn't have a callable interface and may or may not answer a result -- for processing of input. If the response is not a monad, it'll be automatically wrapped as a `Success`. Example:



[source,ruby]

----

Model = Struct.new :label, keyword_init: true do

  include Dry::Monads[:result]



  def self.for(...) = Success new(...)

end



pipe({label: "Test"}, to(Model, :for))    # Success #

pipe Failure("Danger!"), to(Model, :for)  # Failure "Danger!"

----



===== Try



Allows you to try an operation which may fail while catching the exception as a failure for further processing. Example:



[source,ruby]

----

pipe "test", try(:to_json, catch: JSON::ParserError)     # Success "\"test\""

pipe "test", try(:invalid, catch: NoMethodError)         # Failure "undefined method..."

pipe Failure("Danger!"), try(:to_json, catch: JSON::ParserError)  # Failure "Danger!"

----



===== Use



Allows you to use another transaction which might have multiple steps of it's own, use an object that adheres to the {command_pattern_link}, or any function which answers a {dry_monads_link} `Result` object. In other words, you can use _use_ any object which responds to `#call` and answers a {dry_monads_link} `Result` object. This is great for chaining multiple transactions together.



[source,ruby]

----

function = -> input { Success input * 3 }



pipe 3, use(function)                   # Success 9

pipe Failure("Danger!"), use(function)  # Failure "Danger!"

----



===== Validate



Allows you to use an operation that will validate the input. This is especially useful when using {dry_schema_link}, {dry_validation_link}, or any operation that can respond to `#call` while answering a result that can be converted into a hash.



By default, the `:as` key uses `:to_h` as it's value so you get automatic casting to a `Hash`. Use `nil`, as the value, to disable this behavior. You can also pass in any value to the `:as` key which is a valid method that the result will respond to.



[source,ruby]

----

schema = Dry::Schema.Params { required(:label).filled :string }



pipe({label: "Test"}, validate(schema))           # Success label: "Test"

pipe({label: "Test"}, validate(schema, as: nil))  # Success #"Test"} errors={} path=[]>

pipe Failure("Danger!"), validate(schema)         # Failure "Danger!"

----



==== Advanced



Several options are available should you need to advance beyond the basic steps. Each is described in detail below.



===== Procs



You can always use a `Proc` as a custom step. Example:



[source,ruby]

----

include Transactable

include Dry::Monads[:result]



pipe :a,

     insert(:b),

     proc { Success "input_ignored" },

     as(:to_sym)



# Yields: Success :input_ignored

----



ℹī¸ While procs are effective, you are limited in what you can do with them in terms of additional behavior and instrumentation support.



===== Lambdas



In addition to procs, lambdas can be used too. Example:



[source,ruby]

----

include Transactable



pipe :a,

     insert(:b),

     -> result { result.fmap { |input| input.join "_" } },

     as(:to_sym)



# Yields: Success :a_b

----



ℹī¸ Lambdas are a step up from procs but, like procs, you are limited in what you can do with them in terms of additional behavior and instrumentation support.



===== Methods



Methods -- in addition to procs and lambdas -- are the _preferred_ way to add custom steps due to the concise syntax. Example:



[source,ruby]

----

class Demo

  include Transactable



  def call input

    pipe :a,

         insert(:b),

         :join,

         as(:to_sym)

  end



  private



  def join(result) = result.fmap { |input| input.join "_" }

end



Demo.new.call :a  # Yields: Success :a_b

----



All methods can be referenced by symbol as shown via `:join` above. Using a symbol is syntactic sugar for link:https://rubyapi.org/o/object#method-i-method[Object#method] so the use of the `:join` symbol is the same as using `method(:join)`. Both work but the former requires less typing than the latter.



ℹī¸ You won't be able to instrument these method calls (unless you inject instrumentation) but are great when needing additional behavior between the default steps.



===== Custom



If you'd like to define permanent and reusable steps, you can register a custom step which requires you to:



. Define a custom step as a new class.

. Register your custom step along side the existing default steps.



Here's what this would look like:



[source,ruby]

----

module MySteps

  class Join < Transactable::Steps::Abstract

    def initialize(delimiter = "_", **)

      super(**)

      @delimiter = delimiter

    end



    def call(result) = result.fmap { |input| input.join delimiter }



    private



    attr_reader :delimiter

  end

end



Transactable::Steps::Container.register(:join) { MySteps::Join }



include Transactable



pipe :a, insert(:b), join, as(:to_sym)

# Yields: Success :a_b



pipe :a, insert(:b), join(""), as(:to_sym)

# Yields: Success :ab

----



=== Containers



Should you not want the basic steps, need custom steps, or a hybrid of basic and custom steps, you can define your own container and provide it as an argument to `.with` when including transactable behavior. Example:



[source,ruby]

----

require "dry/container"



module MyContainer

  extend Dry::Container::Mixin



  register :echo, -> result { result }

  register(:insert) { Transactable::Steps::Insert }

end



include Transactable.with(MyContainer)



pipe :a, echo, insert(:b)



# Yields: Success [:a, :b]

----



The above is a hybrid example where the `MyContainer` registers a custom `echo` step along with the default `insert` step to make a new container. This is included when passed in as an argument via `.with` (i.e. `include Transactable.with(MyContainer)`).



Whether you use default, custom, or hybrid steps, you have maximum flexibility using this approach.



=== Composition



Should you ever need to make a plain old Ruby object functionally composable, then you can _include_ the `Transactable::Composable` module which will give you the necessary `\#>>`, `#<<`, and `#call` methods where you only need to implement the `#call` method.



=== Instrumentation



Each transaction includes instrumentation using {dry_events_link} which you can subscribe to or ignore entirely. The following events are supported:



* `step`: Published for each step regardless of success or failure.

* `step.success`: Published for success steps only.

* `step.failure`: Published for failure steps only.



Using the example code at the start of this _Usage_ section, here's how you can subscribe to events emitted by the transaction:



[source,ruby]

----

Transactable::Instrument::EVENTS.each do |name|

  Transactable::Container[:instrument].subscribe name do |event|

    puts "#{event.id}: #{event.payload}"

  end

end

----



Now, as before, you can call the transaction with subscribers enabled:



[source,ruby]

----

demo.call csv

----



The above will then yield the following results in your console:



....

step: {:name=>"Transactable::Steps::Check", :arguments=>[[], {}, nil]}

step.success: {:name=>"Transactable::Steps::Check", :value=>"Book,Author,Price,At\nMystics,urGoh,10.50,2022-01-01\nSkeksis,skekSil,20.75,2022-02-13\n", :arguments=>[[], {}, nil]}

step: {:name=>"Transactable::Steps::Map", :arguments=>[[], {}, #]}

step.success: {:name=>"Transactable::Steps::Map", :value=>["Mystics: 10.50", "Skeksis: 20.75"], :arguments=>[[], {}, #]}

....



Finally, the `Transactable::Instrumentable` module is available should you need to _prepend_ instrumentation to any of your class' `#call` methods.



There is a lot you can do with instrumentation so check out the {dry_events_link} documentation for further details.



== Development



To contribute, run:



[source,bash]

----

git clone https://github.com/bkuhlmann/transactable

cd transactable

bin/setup

----



You can also use the IRB console for direct access to all objects:



[source,bash]

----

bin/console

----



=== Architecture



The architecture of this gem is built on top of the following concepts and gems:



* {function_composition_link}: Made possible through the use of the `\#>>` and `#<<` methods on the link:https://rubyapi.org/3.1/o/method[Method] and link:https://rubyapi.org/3.1/o/proc[Proc] objects.

* {dry_container_link}: Allows related dependencies to be grouped together for injection as desired.

* {dry_events_link}: Allows all steps to be observable so you can subscribe to any/all events for metric, logging, and other capabilities.

* {dry_monads_link}: Critical to ensuring the entire pipeline of steps adhere to the {railway_pattern_link} and leans heavily on the `Result` object.

* link:https://dry-rb.org/gems/dry-transaction[Dry Transaction]: Specifically the concept of a _step_ where each step can have an _operation_ and/or _input_ to be processed. Instrumentation is used as well so you can have rich metrics, logging, or any other kind of observer wired up as desired.

* link:https://alchemists.io/projects/infusible[Infusible]: Coupled with {dry_container_link}, allows dependencies to be automatically injected.

* link:https://alchemists.io/projects/marameters[Marameters]: Through the use of the `.categorize` method, dynamic message passing is possible by inspecting the operation method's parameters.



=== Style Guide



* *Transactions*

** Use a single method (i.e. `#call`) which is public and adheres to the {command_pattern_link} so transactions can be piped together if desired.

* *Steps*

** Inherit from the `Abstract` class in order to gain monad, composition, and dependency behavior. Any dependencies injected are automatically filtered out so all subclasses have direct and clean access to the base positional, keyword, and block arguments. These variables are prefixed with `base_*` in order to not conflict with subclasses which might only want to use non-prefixed variables for convenience.

** All filtered arguments -- in other words, the unused arguments -- need to be passed up to the superclass from the subclass (i.e. `super(*positionals, **keywords, &block)`). Doing so allows the superclass (i.e. `Abstract`) to provide access to `base_positionals`, `base_keywords`, and `base_block` for use if desired by the subclass.

** The `#call` method must define a single positional `result` parameter since a monad will be passed as an argument. Example: `def call(result) = # Implementation`.

** Each block within the `#call` method should use the `input` parameter to be consistent. More specific parameters like `argument` or `operation` should be used to improve readability when possible. Example: `def call(result) = result.bind { |input| # Implementation }`.

** Use implicit blocks sparingly. Most of the default steps shy away from using blocks because it can make the code more complex. Use private methods, custom steps, and/or separate transactions if the code becomes too complex because you might have a smaller object which needs extraction.



=== Debugging



If you need to debug (i.e. {debug_link}) your pipe, use a lambda. Example:



[source,ruby]

----

pipe data,

     check(/Book.+Price/, :match?),

     -> result { binding.break },    # Breakpoint

     :parse

----



The above breakpoint will allow you inspect the result of the `#check` step and/or build a modified result for passing to the subsequent `#method` step.



=== Troubleshooting



The following might be of aid to as you implement your own transactions.



==== Type Errors



If you get a `TypeError: Step must be functionally composable and answer a monad`, it means:



. The step must be a `Proc`, `Method`, or some object which responds to `\#>>`, `#<<`, and `#call`.

. The step doesn't answer a result monad (i.e. `Success some_value` or `Failure some_value`).



==== No Method Errors



If you get a `NoMethodError: undefined method `success?` exception, it might mean that you forgot to add a comma after one of your steps. Example:



[source,ruby]

----

# Valid

pipe "https://www.wikipedia.org",

     to(client, :get),

     try(:parse, catch: HTTP::Error)



# Invalid

pipe "https://www.wikipedia.org",

     to(client, :get)  # <= Comma is missing on this line.

     try(:parse, catch: HTTP::Error)

----



== Tests



To test, run:



[source,bash]

----

bin/rake

----



== Benchmarks



To view/compare performance, run:



[source,bash]

----

bin/benchmark

----



💡 You can view current benchmarks at the end of the above file if you don't want to manually run them.



== link:https://alchemists.io/policies/license[License]



== link:https://alchemists.io/policies/security[Security]



== link:https://alchemists.io/policies/code_of_conduct[Code of Conduct]



== link:https://alchemists.io/policies/contributions[Contributions]



== link:https://alchemists.io/projects/transactable/versions[Versions]



== link:https://alchemists.io/community[Community]



== Credits



* Built with link:https://alchemists.io/projects/gemsmith[Gemsmith].

* Engineered by link:https://alchemists.io/team/brooke_kuhlmann[Brooke Kuhlmann].