With Active Model Serializers, how do you render a partial? - ruby-on-rails-4

Question

I'm creating a newsfeed and have a JSON response set up with Active Model Serializers gem. I'd like to render a regular ERB partial and have it as one of the attributes in the JSON.
controllers/posts_controller.rb:
def index
#posts = Post.all
respond_to do |format|
format.json { render json: #posts.to_a, each_serializer: PostSerializer }
end
end
serializers/post_serializer.rb:
def event_html
ApplicationController.new.render_to_string(:partial => 'events/event', :locals => { :event => object.event }) if object.event
end
Unfortunately, my view has some code that uses helpers and the request object (urls), and I'm getting errors when I try to do this.
events/_event.html.erb:
<div class="event">
<h4 class="title"><%= link_to event.name, event %></h4>
<div class="date"><%= date_range event.start_at, event.end_at %></div>
<div class="description"><%= event.description.html_safe %></div>
</div>
undefined method `host' for nil:NilClass
Any ideas of a good way to solve this problem?

Answer 1

That happens because your controller lacks response attribute.
You may set the request for the controller as follows:
def event_html
ApplicationController.new.tap {|c|
c.request = ActionController::TestRequest.new(host: "localhost")
}.render_to_string(:partial => 'events/event', :locals => { :event => object.event }) if object.event
end
However, for your case I would pass an existing controller as a context to the serializer
controllers/posts_controller.rb:
def index
#posts = Post.all
respond_to do |format|
format.json { render json: #posts.to_a, each_serializer: PostSerializer, context: self }
end
end
# ... or ...
def default_serializer_options
{
context: self
}
end
serializers/post_serializer.rb:
def event_html
context.render_to_string(:partial => 'events/event', :locals => { :event => object.event }) if object.event
end