Friendly.rb - Your friendly European Ruby Conference Execution context ​
Avo enables developers to hook into different points of the application lifecycle using blocks. That functionality can't always be performed in void but requires some pieces of state to set up some context.
Computed fields are one example.
field :full_name, as: :text do
"#{record.first_name} #{record.last_name}"
endIn that block we need to pass the record so you can compile that value. We send more information than just the record, we pass on the resource, view, view_context, request, current_user and more depending on the block that's being run.
How does the ExecutionContext work? ​
The ExecutionContext is an object that holds some pieces of state on which we execute a lambda function.
module Avo
class ExecutionContext
attr_accessor :target, :context, :params, :view_context, :current_user, :request
def initialize(**args)
# If target don't respond to call, handle will return target
# In that case we don't need to initialize the others attr_accessors
return unless (@target = args[:target]).respond_to? :call
args.except(:target).each do |key,value|
singleton_class.class_eval { attr_accessor "#{key}" }
instance_variable_set("@#{key}", value)
end
# Set defaults on not initialized accessors
@context ||= Avo::Current.context
@params ||= Avo::Current.params
@view_context ||= Avo::Current.view_context
@current_user ||= Avo::Current.current_user
@request ||= Avo::Current.request
end
delegate :authorize, to: Avo::Services::AuthorizationService
# Return target if target is not callable, otherwise, execute target on this instance context
def handle
target.respond_to?(:call) ? instance_exec(&target) : target
end
end
end
# Use it like so.
SOME_BLOCK = -> {
"#{record.first_name} #{record.last_name}"
}
Avo::ExecutionContext.new(target: &SOME_BLOCK, record: User.first).handleThis means you could throw any type of object at it and it it responds to a call method wil will be called with all those objects.
-> target
The block you'll pass to be evaluated. It may be anything but will only be evaluated if it responds to a call method.
-> context
Aliased to Avo::Current.context.
-> current_user
Aliased to Avo::Current.user.
-> view_context
Aliased to Avo::Current.view_context.
-> request
Aliased to Avo::Current.request.
-> params
Aliased to Avo::Current.params.
-> Custom variables
You can pass any variable to the ExecutionContext and it will be available in that block. This is how we can expose view, record, and resource in the computed field example.
Avo::ExecutionContext.new(target: &SOME_BLOCK, record: User.first, view: :index, resource: resource).handle-> helpers
Within the ExecutionContext you might want to use some of your already defined helpers. You can do that using the helpers object.
# products_helper.rb
class ProductsHelper
# Strips the "CODE_" prefix from the name
def simple_name(name)
name.gsub "CODE_", ""
end
end
field :name, as: :text, format_using: -> { helpers.simple_name(value) }