Rails pagination in API using Her, Faraday - ruby

Question

I've been trying to figure this out all day, and it's driving me crazy.
I have two rails apps, ServerApp and ClientApp. ClientApp gets data from ServerApp through an API, using the Her gem. Everything was great until I needed pagination information.
This is the method I am using to get the orders (this uses kamainari for pagination and ransack for search):
# ServerApp
def search
#search = Order.includes(:documents, :client).order('id desc').search(params[:q])
#orders = #search.result(distinct: true).page(params[:page]).per(params[:per])
respond_with #orders.as_json(include: :documents)
end
It returns an array of hashes in json, which Her uses as a collection of orders. That works fine.
# Response
[
{
"client_id": 239,
"created_at": "2013-05-15T15:37:03-07:00",
"id": 2422,
"ordered_at": "2013-05-15T15:37:03-07:00",
"origin": "online",
"updated_at": "2013-05-15T15:37:03-07:00",
"documents": [
{ ... }
]
},
...
]
But I needed pagination information. It looked like I needed to send it as metadata with my json. So I change my response to this:
respond_to do |format|
format.json do
render json: { orders: #orders.as_json(include: :documents), metadata: 'sent' }
end
end
This does indeed send over metadata, so in my ClientApp I can write #orders.metadata and get 'sent'. But now my orders are nested in an array inside of 'orders', so I need to use #orders.orders, and then it treats it like an array instead of a Her collection.
After doing some reading, it seemed sending pagination info through headers was the way a lot of other people did this (I was able to get the headers set up in an after_filter using this guide). But I am even more lost on how to get those response headers in my ClientApp - I believe I need a Faraday Middleware but I just am having no luck getting this to work.
If anyone knows how I can just get this done, I would be very grateful. I can't take another day of banging my head against the wall on this, but I feel like I am just one vital piece of info away from solving this!

Answer 1

I encountered the same issue and solved it by adding my own middleware and rewriting the "parse" and "on_complete" methods without that much hassle and avoiding the use of global variables.
Here's the code:
class CustomParserMiddleware < Her::Middleware::DefaultParseJSON
def parse(env)
json = parse_json(env[:body])
pagination = parse_json(env[:response_headers][:pagination_key]) || {}
errors = json.delete(:errors) || {}
metadata = json.delete(:metadata) || {}
{
:data => json,
:errors => errors,
:metadata => {
:pagination => pagination,
:additional_metadata => metadata
},
end
def on_complete(env)
env[:body] = case env[:status]
when 204
parse('{}')
else
parse(env)
end
end
end
then, you can access the pagination as follows:
model = Model.all
model.metadata[:pagination]

Answer 2

I finally got this working. The trick was to use a global variable in the faraday on_complete - I tried to find a better solution but this was the best I could do. Once again, I got the header code from here. Here's the full guide to how to get pagination working with Her:
First, on my server side, I have the Kaminari gem, and I pass page and per as params to the server from the client. (This is also using ransack for searching)
def search
#search = Order.order('id desc').search(params[:q])
#orders = #search.result(distinct: true).page(params[:page]).per(params[:per])
respond_with #orders.as_json(include: :items)
end
My client makes the request like so:
#orders = Order.search(q: { client_id_eq: #current_user.id }, page: params[:page], per: 3)`
Back on the server, I have this in my ApiController (app controller for api):
protected
def self.set_pagination_headers(name, options = {})
after_filter(options) do |controller|
results = instance_variable_get("##{name}")
headers["X-Pagination"] = {
total_count: results.total_count,
offset_value: results.offset_value
}.to_json
end
end
In the server orders_controller.rb, I set the pagination headers for the search method:
class OrdersController < ApiController
set_pagination_headers :orders, only: [:search]
...
end
Now to receive the headers we need a Faraday middleware in Her on the client.
# config/initializers/her.rb
Her::API.setup url: Constants.api.url do |c|
c.use TokenAuthentication
c.use HeaderParser # <= This is my middleware for headers
c.use Faraday::Request::UrlEncoded
c.use Her::Middleware::DefaultParseJSON
c.use Faraday::Adapter::NetHttp
c.use Faraday::Response::RaiseError
end
# lib/header_parser.rb
# don't forget to load this file in application.rb with something like:
# config.autoload_paths += Dir[File.join(Rails.root, "lib", "*.rb")].each { |l| require l }
class HeaderParser < Faraday::Response::Middleware
def on_complete(env)
unless env[:response_headers]['x-pagination'].nil?
# Set the global var for pagination
$pagination = JSON.parse(env[:response_headers]['x-pagination'], symbolize_names: true)
end
end
end
Now back in your client controller, you have a global variable of hash called $pagination; mine looks like this:
$pagintation = { total_count: 0, offset_value: 0 }`
Finally, I added Kaminari gem to my client app to paginate the array and get those easy pagination links:
#orders = Kaminari.paginate_array(#orders, total_count: $pagination[:total_count]).page(params[:page]).per(params[:per_page])`
I hope this can help someone else, and if anyone knows a better way to do this, let me know!

Answer 3

You can pass header options to Faraday when setting up the connection, see the docs at http://rubydoc.info/gems/faraday/0.8.7/Faraday/Connection:initialize
Sometimes it helps to do a curl request first, esp. use -vv option for verbose output where you will see all headers. (Maybe you can attach some log outputs from the Server too)
You can use e.g. clogger (http://clogger.rubyforge.org/) do monitor header information on the Rails server side