Regardless of whether you use declared Reflexes in your HTML markup or call
stimulate() directly from inside of a Stimulus controller, StimulusReflex maps your requests to Reflex classes on the server. These classes are found in
app/reflexes and they inherit from
class ExampleReflex < ApplicationReflex end
Setting a declarative data-reflex="click->Example#test" will call the
test method in the Example Reflex class. We refer to Reflex class methods which get called from the client as "Reflex Action methods".
You can do anything you like in a Reflex action, including retrieving data from Redis, ActiveRecord database updates, launching ActiveJobs and even initiating CableReady broadcasts.
If you change the code in a Reflex class, you have to refresh your web browser to allow ActionCable to reconnect. This will reload the appropriate modules and allow you to see your changes.
You can get and set values on the
session object, and if you're using the (default) Page Morph Reflexes, any instance variables that you set in your Reflex Action method will be available to the controller action before your page is re-rendered.
class ExampleReflex < ApplicationReflex def test @id = element.dataset["id"] # @id will be available inside your controller action if you're doing a Page Morph end end
You will learn all about the
element accessor in the next section.
Note that there's no correlation between the Reflex class or Reflex action and the page (or its controller) that you're on. Your
users#show page can call
ActionCable Connection Identifiers
It's very common to want to be able to access the
current_user or equivalent accessor inside your Reflex actions. First, you'll need to make sure that your Connection is "identified" by your
current_user. Since ActionCable is separate from the ActionController namespace, accessors need to be setup as part of your authentication process.
Your Connection can have multiple accessors defined. For example, it's common to implement a hybrid technique to use the visitor's
session_id before they authenticate, and then switch over to
Once your connection is
identified_by :current_user, you can delegate
current_user to your ActionCable Connection:
class ExampleReflex < ApplicationReflex delegate :current_user, to: :connection def increment current_user.counter.increment! end end
If you plan to access
current_user from all of your Reflex classes, delegate it your ApplicationReflex:
class ApplicationReflex < StimulusReflex::Reflex delegate :current_user, to: :connection end
Queries and associations are cached
identified_by accessors such as
current_user, it's important to remember that any ActiveRecord queries or associations you access will be cached by default, even across multiple Reflexes.
The cache is cleared when the ActionCable Connection is re-established (usually with a page refresh) or you manually force the accessor to reload its associations:
You can also bust the cached value by running a different query, but Rails developers are used to thinking in terms of request/response cycles. They know controller actions are idempotent, and so it's reasonable to expect Reflex actions to also be idempotent. And they are... except for accessors on the Connection.
current_user or other Connection identifiers in templates or partials that will be rendered in a Reflex.
Instead, pass a
user variable into the template using the
locals hash parameter.
If you are expecting your data to change and it doesn't, you can lose an afternoon to debugging.
Likewise, if you keep this potential gotcha in the back of your mind, it's entirely fair to see this association caching behavior as a performance boost. After all, it's one less query to run! 😅
Building your Reflex action
The following properties available to the developer inside Reflex actions:
connection- the ActionCable connection
channel- the ActionCable channel
ActionDispatch::Requestproxy for the socket connection
ActionDispatch::Sessionstore for the current visitor
ActionDispatch::Flash::FlashHashfor the current request
url- the URL of the page that triggered the reflex
ActionController::Parametersof the closest form
element- a Hash like object that represents the HTML element that triggered the reflex
reflex_id- a UUIDv4 that uniquely identies each Reflex
process are reserved words inside Reflex classes. You cannot create Reflex actions with these names.
element property contains all of the Stimulus controller's DOM element attributes as well as other properties like
value. In addition,
values and the
dataset property reference special collections as described below.
Most values are strings. The only exceptions are
selected which are booleans.
Elements that support multiple values such as
<select multiple> or a collection of checkboxes with the same
name will emit an additional
values property. In addition, the
value property will contain a comma-separated string of the checked options.
Here's an example that outlines how you can interact with the
element property and the
dataset collection in your Reflex action. You can use the dot notation as well as string and symbol accessors.
<input type="checkbox" id="example" label="Example" checked data-reflex="change->Example#accessors" data-value="123" />
class ExampleReflex < ApplicationReflex def accessors element.id # => "example" element[:id] # => "example" element["id"] # => "example" element.value # => "on" (checkbox is always "on", use checked) element.values # => nil, or Array for multiple values element[:tag_name] # => "CHECKBOX" element[:checked] # => true element["checked"] # => true element.checked # => true element.label # => "Example" element.data_reflex # => "change->Example#accessors" element["data-reflex"] # => "change->Example#accessors" element.dataset[:reflex] # => "change->Example#accessors" element.dataset["reflex"] # => "change->Example#accessors" element.dataset.value # => "123" element.data_value # => "123" element["data-value"] # => "123" element.dataset[:value] # => "123" element.dataset["value"] # => "123" end end
data-id are different attributes.
id can be used as a CSS selector, and it must be unique in your DOM. It does not show up in your
data-id cannot be used as a CSS selector, does not have to be unique in your DOM and is part of your
dataset. Similar names, entirely different concepts and functions.
The same goes for other pairs, such as
value has meaning to the browser and it's what gets processed in a form submission by Rails.
data-value is just an arbitrary name that you made up, and it could have just as easily been
When StimulusReflex is rendering your template, an instance variable named @stimulus_reflex is available to your Rails controller and set to true.
You can use this flag to create branching logic to control how the template might look different if it's a Reflex vs normal page refresh.
Signed and unsigned Global ID accessors
Rails has a pair of cool features that allow developers to generate tokens from ActiveRecord models. These tokens can later be used to access those models, and in the case of signed Global IDs, obscure the model from prying eyes. They can even be set to expire after a period of time.
element accessor on every Reflex has two dynamic accessors,
unsigned which automatically unpack Global IDs stored in data attributes and converts them to model instances.
<div data-reflex="click->Example#foo" data-public="<%= @foo.to_global_id.to_s %>" data-secure="<%= @foo.to_sgid.to_s %>" >
While in reality, you'd never use both on the same object, you can now have StimulusReflex automatically convert these attributes into instances of the models they reference. This happens lazily, at the time you access the accessor:
class ExampleReflex < ApplicationReflex def foo puts element.unsigned[:public] # returns Foo model instance puts element.signed[:secure] # returns Foo model instance end end
While most developers default to using signed Global IDs, understand that the tradeoff is that signed tokens can be quite long, whereas unsigned tokens remain short.
Reflex exceptions are rescuable
If you'd like to wire up 3rd-party exception handling services like Sentry or HoneyBadger to your Reflex classes, you can use
rescue_from to respond to an errors raised.
class MyTestReflex < ApplicationReflex rescue_from StandardError do |exception| ExceptionTrackingService.error(exception) end # ... end
Every Reflex starts as a client-side data structure that is assigned a unique UUIDv4 used to track it through its round-trip life-cycle. Most developers using StimulusReflex never have to think about these details. However, if you're building an application that is based on transactional concepts, it might be very useful to be able to track interactions based on the
class ExampleReflex < ApplicationReflex def foo puts reflex_id end end