Transflow
Business transaction flow DSL. The aim of this small gem is to provide a simple way of defining complex business transaction flows that include processing by many different objects.
It is based on the following ideas:
- a business transaction is a series of operations where each can fail and stop processing
- a business transaction resolves its dependencies using an external container object and it doesn’t know any details about the individual operation objects except their identifiers
- a business transaction can describe the flow on an abstract level without being coupled to any details about how individual operations work
- a business transaction doesn’t have any state
- each operation shouldn’t accumulate state, instead it should receive an input and return an output without causing any side-effects
- the only interface of a an operation is
#call(input)
- each operation provides a meaningful functionality and can be reused
- each operation can broadcast its result
- external message consumers can listen to a transaction object for specific events
Why?
The rationale for this project is quite simple - every use-case in an application can be described as a series of processing steps where some input is turned into an output. Steps can result in triggering additional operations handled by other parts of your application or completely external systems and that can be easily handled by a pub/sub interface.
It’s a clean and simple way of encapsulating complex business logic in your application using simple, stateless objects.
Error Handling
This will be the tricky part - there are scenarios where we need to aggregate errors from multiple steps without stopping the processing. It’s not implemented yet but probably using pub/sub for that will do the work as we can register an error listener that can simply gather errors and return it as a result.
Synopsis
Using Transflow is ridiculously simple as it doesn’t make much assumptions about
your code. You provide container with operations and they simply need to respond
to #call(input)
and return output or raise an error if something went wrong.
Defining a simple flow
``` ruby DB = []
container = { validate: -> input { input[:name].nil? ? raise(“name nil”) : input }, persist: -> input { DB « input[:name] } }
my_business_flow = Transflow(container: container) { steps :validate, :persist }
my_business_flow[{ name: ‘Jane’ }]
puts DB.inspect # [“Jane”] ```
Defining a flow with event publishers
In many cases an individual operation may require additional behavior to be
triggered. This can be easily achieved with a pub/sub mechanism. Transflow
provides that mechanism through the wonderful wisper
gem which is used under
the hood.
``` ruby DB = []
NOTIFICATIONS = [] # just for the sake of the example
class UserPersistListener def self.persist_success(user) NOTIFICATIONS « ”#user persisted” end
def self.persist_failure(user, err) # do sth about that end end
my_business_flow = Transflow(container: container) do step(:validate) { step(:persist, publish: true) } end
my_business_flow.subscribe(persist: UserPersistListener)
my_business_flow[{ name: ‘Jane’ }]
puts DB.inspect # [“Jane”]
puts NOTIFICATIONS.inspect # [“Jane persisted”] ```
Passing additional arguments
Another common requirement is to pass aditional arguments that we don’t have in
the moment of defining our flow. Fortunately Transflow allows you to pass any
arguments in the moment you call the transaction. Those arguments will be curried
which means you must use either procs as your operation or an object that responds
to curry
. This limitation will be removed soon.
``` ruby DB = []
operations = {
preprocess_input: -> input { { name: input[‘name’], email: input[‘email’] } },
# let’s say this one needs additional argument called email
validate_input: -> email, input { input[:email] == email ? input : raise(‘ops’) },
persist_input: -> input { DB « input[:name] }
}
transflow = Transflow(container: operations) do step :preprocess, with: :preprocess_input do step :validate, with: :validate_input do step :persist, with: :persist_input end end end
input = { ‘name’ => ‘Jane’, ‘email’ => ‘[email protected]’ }
here we say “for validate
operation curry this additional argument
transflow[input, validate: ‘[email protected]’]
puts DB.inspect # [“Jane”] ```
Installation
Add this line to your application’s Gemfile:
ruby
gem 'transflow'
And then execute:
$ bundle
Or install it yourself as:
$ gem install transflow
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/solnic/transflow.