Context
Use a context object to provide shared facilities to every template, partial, scope, and part in a given view rendering.
A context object is helpful in holding any behaviour or data you don't want to pass around explicitly. For example:
- Data specific to the current HTTP request, like the request path and CSRF tags
- A "current user" or similar session-based object needed across multiple disparate places
- Application static assets helpers
content_for
-style helpers
Defining a context
Context classes must inherit from Dry::View::Context
class MyContext < Dry::View::Context
end
Injecting dependencies
Dry::View::Context
is designed to allow dependencies to be injected into your subclasses. To do this, accept your dependencies as keyword arguments to #initialize
, and pass every other keyword argument through to super
:
class MyContext < Dry::View::Context
attr_reader :assets
def initialize(assets:, **args)
@assets = assets
super(**args)
end
def asset_path(asset_name)
assets[asset_name]
end
end
If your app uses dry-system or dry-auto_inject, this is even less work. dry-auto_inject works out of the box with Dry::View::Context
’s initializer:
# Require the auto-injector module for your app's container
require "my_app/import"
class MyContext < Dry::View::Context
include MyApp::Import["assets"]
def asset_path(asset_name)
assets[asset_name]
end
end
Providing the context
The default context can be configured
for a view:
class MyView < Dry::View
config.default_context = MyContext.new
end
Or provided at render-time, when calling a view:
my_view.call(context: my_context)
This context object will override whatever has been previously configured.
When providing a context at render time, you may wish to provide a version of your context object with e.g. data specific to the current HTTP request, which is not available when configuring the view with a context.
Decorating context attributes
Your context may have attribute that you want decorated as parts. Declare these using decorate
in your context class:
class MyContext < Dry::View::Context
decorate :navigation_items
attr_reader :navigation_items
def initialize(navigation_items:, **args)
@navigation_items = navigation_items
super(**args)
end
end
You can pass the same options to decorate
as you do to exposures, for example:
class MyContext < Dry::View::Context
decorate :navigation_items, as: :menu_items
# ...
end