BraceComb

Brace Comb is a small bit of wax built between two combs or frames to fasten them together. Brace comb is also built between a comb and adjacent wood, or between two wooden parts such as top bars.

This is akin to how workflows are connected to each other with dependencies.

In workflow management systems, there is often a need to define that certain tasks should only begin when another task(s) is complete. BraceComb can be used to define multiple types of workflows and handle each workflow consistently.

A factory production line system uses pre-defined workflows with strict dependencies between tasks. In a simplified scenario, let's say we need to define a workflow in which an item on the conveyor belt must be packed before it is dispatched. In this case:

• Dependents/Tasks are the actions such as packing and dispatching
• Dependencies are links that define that packing must finish before dispatching

In this system we can create a dependent entity called tasks of type packing and another dependent entity tasks of type dispatching. A new task_dependency entity between the two entities can be created using the following command:

  initialize_dependency! from: task1.id, to: task2.id, dependency_type: 'dispatch'

dependency_type is used to categorize the dependency. This will create a task_dependency entity in pending state. In this case packing task is a strict prerequisite for dispatching task, hence dispatching should not start unless packing is complete. Therefore the task_dependency between them should be in resolved state. This is also the case for any dependencies of dependency_type dispatch. This relationship can be defined by declaring a dependency characteristics on the task_dependency class using:

  declare_dependency type: :dispatch,
                     resolver: :send_packing_complete_confirmation,
                     before_resolution: [:check_packing_complete?, :check_dispatcher_available?],
                     after_resolution: [:send_dispatch_notification]

This declaration will ensure that for all dependencies of type dispatch, when the task_dependency is marked as resolved, all before_resolution hooks are first run. If any before_resolution functions returns false, then the operation is aborted. If all before_resolution functions return true, then the resolver code inside send_packing_complete_confirmation will be executed, and then all functions inside after_resolution would be executed.

To kick-off this flow just call task_dependency.resolve and the before and after hooks will be invoked in the manner as described above.

1. Add to your Gemfile.

   gem 'brace_comb'

2. Create an initializer for brace_comb

   a. bundle exec rails generate brace_comb:initializer

   b. Modify the name of dependency and dependent tables in the initializer config/initializers/brace_comb.rb

   c. Run bundle exec rails generate brace_comb:migration to create the migration

   d. Create the dependency tables and associations using bundle exec rake db:migrate

   e. Generate the basic dependency model by running: bundle exec rails generate brace_comb:model <insert model name here>

Entity names for dependencies and dependents are configurable and can be set in config/initializers/brace_comb.rb before creating the migrations.

1. Declare a dependency type by adding in the following to the dependency (task_dependency) class:

     include BraceComb::Model
   

2. Declare a dependency by typing in the following in any ActiveRecord class. Only resolver is compulsory whereas before_resolution and after_resolution are optional. type is a unique string and is used to identify the resolution behaviour for all dependents with dependency_type the same as that defined in type.

   a. Using a method name in the resolver

     declare_dependency type: :shopping,
                        resolver: :shopping_complete
                        before_resolution: [:completed_status?],
                        after_resolution: [:complete_job]
   

   or

   b. Using a proc in the resolver

     declare_dependency type: :shopping,
                        resolver: ->(data) { data.condition },
                        before_resolution: [:completed_status?],
                        after_resolution: [:complete_job]
   

3. Create dependencies between the dependent class by using the following helper in any instance method of a model class:

   • When an exception needs to be raised: initialize_dependency! from: task1.id, to: task2.id, type: 'shopping'

   or

   • When a boolean needs to be returned: initialize_dependency from: task1.id, to: task2.id, type: 'shopping'

4. Resolve dependencies from any active record model by using:

   • When an exception needs to be raised:

     dependency.resolve!(identifier: 123, status: :resolved)
   

   or

   • When a boolean needs to be returned:

     dependency.resolve(identifier: 123, status: :resolved)
   

   Any arguments passed to resolve! methods will be directly sent to the resolver. So arguments should be sent based on the resolver definition

• Allowing dependency declaration to accept multiple resolvers, and allowing resolve to accept the name of the resolver. This could possibly by done in resolve method itself instead of declare_dependency
• Combining the installation steps into 1-2 steps
• And more...

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

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