Accept a lambda for context in factory

[haines]

Like decorates_association, you can now pass a context lambda to decorates_assigned, which receives the current controller instance and returns a hash:

class ArticleController < ApplicationController
  decorates_assigned :article, context: ->(controller){ {user: controller.current_user} }
end

The actual calling of the lambda has been extracted to the Factory·

Closes #467

[steveklabnik]

👍 I like the symmetry.

[urbanautomaton]

There's a minor problem here, unfortunately, due to the way ruby destructures hashes with splats:

> def splat(*args); args; end
=> nil
> splat(*{:foo => :bar})
=> [[:foo, :bar]]
> splat(*{:foo => :bar, :baz => :quux})
=> [[:foo, :bar], [:baz, :quux]]

As a result, if I have an owner with context {:foo => :bar}, the decorated association (using the default identity context lambda) will end up with context [:foo, :bar], because Factory splats the context args in #update_context:

class Thing < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base; end

class ThingDecorator
  decorates_association :user
end

class UserDecorator; end

> Thing.first.decorate(:context => { :foo => :bar }).user
=> #<UserDecorator:0x000001030d0ad0
 @context=[:foo, :bar],
 @source=
  #<User id: 1>>

Also, because the identity lambda takes exactly one argument, if I have a more complex context, it raises an ArgumentError:

> Thing.first.decorate(:context => { :foo => :bar, :baz => :quux }).user
ArgumentError: wrong number of arguments (2 for 1)
from <gem_home>/draper/lib/draper/decorated_association.rb:14:in `block in initialize`

Rather than defaulting :context to the identity function and passing the owner's context as :context_args at decoration time, would it work to just pass the owner context in directly at decoration time, like so?

From 507860681dfebb6ee6f2405437d9622412dbec35 Mon Sep 17 00:00:00 2001
From: Simon Coffey
Date: Tue, 19 Feb 2013 14:30:59 +0000
Subject: [PATCH] Pass owner context directly in decorated association

---
 lib/draper/decorated_association.rb       | 4 ++--
 spec/draper/decorated_association_spec.rb | 8 +++-----
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/lib/draper/decorated_association.rb b/lib/draper/decorated_association.rb
index b2e8a1b..7aecd41 100644
--- a/lib/draper/decorated_association.rb
+++ b/lib/draper/decorated_association.rb
@@ -11,7 +11,7 @@ module Draper
       @scope = options[:scope]

       decorator_class = options[:with]
-      context = options.fetch(:context, ->(context){ context })
+      context = options.fetch(:context, {})
       @factory = Draper::Factory.new(with: decorator_class, context: context)
     end

@@ -28,7 +28,7 @@ module Draper
       associated = owner.source.send(association)
       associated = associated.send(scope) if scope

-      @decorated = factory.decorate(associated, context_args: owner.context)
+      @decorated = factory.decorate(associated, context: owner.context)
     end

   end
diff --git a/spec/draper/decorated_association_spec.rb b/spec/draper/decorated_association_spec.rb
index 62b4fed..f15e10b 100644
--- a/spec/draper/decorated_association_spec.rb
+++ b/spec/draper/decorated_association_spec.rb
@@ -28,10 +28,8 @@ module Draper
       end

       describe ":context option" do
-        it "defaults to the identity function" do
-          Factory.should_receive(:new).with do |options|
-            options[:context].call(:anything) == :anything
-          end
+        it "defaults to the empty hash" do
+          Factory.should_receive(:new).with(with: anything(), context: {})
           DecoratedAssociation.new(double, :association, {})
         end
       end
@@ -48,7 +46,7 @@ module Draper
         decorated_association = DecoratedAssociation.new(owner, :association, {})
         decorated = double

-        factory.should_receive(:decorate).with(associated, context_args: owner_context).and_return(decorated)
+        factory.should_receive(:decorate).with(associated, context: owner_context).and_return(decorated)
         expect(decorated_association.call).to be decorated
       end

-- 
1.7.11

[haines]

@urbanautomaton Good catch, thanks.

The suggested patch doesn't work because we want the ability to pass a different context - either a static value decorates_association :something, context: {something: "else"}, or dynamically calculated using a lambda context: ->(owner_context) { owner_context.merge(blah: "blah") }.

I think the best fix is just to Array.wrap the args before splatting them. I think I might also rewrite the specs to be a bit less "stubby" so that things like this don't get through!

[urbanautomaton]

Ah, cool, I wasn't aware of Array.wrap - I'd hesitated to try a fix at the Factory#update_context location because all I could come up with was some gross type inspection. :)