The activity-dsl-linear gem brings:

DSLs strategies for buildig activities. It is build around activity gem.

Please find the full documentation on the Trailblazer website.


The activity-dsl-linear gem provides three default patterns to model processes: Path, Railway and FastTrack. Here's an example of what a railway activity could look like, along with some more complex connections (you can read more about Railway strategy in the docs).

require "trailblazer-activity"
require "trailblazer-activity-dsl-linear"

class Memo::Update < Trailblazer::Activity::Railway
  # here goes your business logic
  def find_model(ctx, id:, **)
    ctx[:model] = Memo.find_by(id: id)

  def validate(ctx, params:, **)
    return true if params[:body].is_a?(String) && params[:body].size > 10
    ctx[:errors] = "body not long enough"

  def save(ctx, model:, params:, **)

  def log_error(ctx, params:, **)
    ctx[:log] = "Some idiot wrote #{params.inspect}"

  # here comes the DSL describing the layout of the activity
  step :find_model
  step :validate, Output(:failure) => End(:validation_error)
  step :save
  fail :log_error

Visually, this would translate to the following circuit.

You can run the activity by invoking its call method.

ctx = { id: 1, params: { body: "Awesome!" } }

signal, (ctx, *) = Update.( [ctx, {}] )

pp ctx #=>
 :model=>#<Memo body=nil>,
 :errors=>"body not long enough"}

pp signal #=> #<struct Trailblazer::Activity::End semantic=:validation_error>

With Activity, modeling business processes turns out to be ridiculously simple: You define what should happen and when, and Trailblazer makes sure that it happens.


  • Activities can model any process with arbitrary flow and connections.
  • Nesting and compositions are allowed and encouraged (via Trailblazer's dsl-linear gem).
  • Different step interfaces, manual processing of DSL options, etc is all possible.
  • Steps can be any kind of callable objects.
  • Tracing! (via Trailblazer's developer gem)


Trailblazer's Operation internally uses an activity to model the processes.


Activities can be formed into bigger compounds and using workflow, you can build long-running processes such as a moderated blog post or a parcel delivery. Also, you don't have to use the DSL but can use the editorinstead(cool for more complex, long-running flows). Here comes a sample screenshot.


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