Fix internals to parse headers on initialization

README.md

@@ -384,7 +384,7 @@ end
 Page based pagination will be deprecated in the `2019-10` API version, in favor of the second method of pagination:
 
 [Relative cursor based pagination](https://help.shopify.com/en/api/guides/paginated-rest-results)
-```
+```ruby
 products = ShopifyAPI::Product.find(:all, params: { limit: 50 })
 process_products(products)
 while products.next_page?

lib/shopify_api/collection_pagination.rb

@@ -1,43 +1,42 @@
 module ShopifyAPI
   module CollectionPagination
 
+    def initialize(args)
+      @previous_url_params = extract_url_params(pagination_link_headers.previous_link)
+      @next_url_params = extract_url_params(pagination_link_headers.next_link)
+      super(args)
+    end
+
     def next_page?
-      next_url_params.present?
+      ensure_available
+      @next_url_params.present?
     end
 
     def previous_page?
-      previous_url_params.present?
+      ensure_available
+      @previous_url_params.present?
     end
 
     def fetch_next_page
-      fetch_page(next_url_params)
+      fetch_page(@next_url_params)
     end
 
     def fetch_previous_page
-      fetch_page(previous_url_params)
+      fetch_page(@previous_url_params)
     end
 
     private
 
     AVAILABLE_IN_VERSION = ShopifyAPI::ApiVersion::Unstable.new
 
     def fetch_page(url_params)
+      ensure_available
       return [] unless url_params.present?
 
       resource_class.where(url_params)
     end
 
-    def previous_url_params
-      @previous_url_params ||= extract_url_params(pagination_link_headers.previous_link)
-    end
-
-    def next_url_params
-      @next_url_params ||= extract_url_params(pagination_link_headers.next_link)
-    end
-
     def extract_url_params(link_header)
-      raise NotImplementedError unless ShopifyAPI::Base.api_version >= AVAILABLE_IN_VERSION
-
       return nil unless link_header.present?
       Rack::Utils.parse_nested_query(link_header.url.query)
     end
@@ -47,5 +46,9 @@ def pagination_link_headers
         ShopifyAPI::Base.connection.response["Link"]
       )
     end
+
+    def ensure_available
+      raise NotImplementedError unless ShopifyAPI::Base.api_version >= AVAILABLE_IN_VERSION
+    end
   end
 end

test/pagination_test.rb

@@ -124,10 +124,9 @@ def setup
   test "raises on invalid pagination links" do
     link_header = "<https://this-is-my-test-shop.myshopify.com/admin/api/unstable/orders.json?page_info=#{@next_page_info}>;"
     fake 'orders', :method => :get, :status => 200, api_version: @version, :body => load_fixture('orders'), :link => link_header
-    orders = ShopifyAPI::Order.all
 
     assert_raises ShopifyAPI::InvalidPaginationLinksError do
-      orders.fetch_next_page
+      ShopifyAPI::Order.all
     end
   end
 
@@ -142,4 +141,43 @@ def setup
       orders.fetch_next_page
     end
   end
+
+  test "allows for multiple concurrent API collection objects" do
+    first_request_params = "page_info=#{@next_page_info}&limit=5"
+    fake(
+      'orders',
+      method: :get,
+      status: 200,
+      api_version: @version,
+      url: "https://this-is-my-test-shop.myshopify.com/admin/api/unstable/orders.json?limit=5",
+      body: load_fixture('orders'),
+      link: "<https://this-is-my-test-shop.myshopify.com/admin/api/unstable/orders.json?#{first_request_params}>; rel=\"next\""
+    )
+    orders = ShopifyAPI::Order.where(limit: 5)
+
+    second_request_params = "page_info=#{@next_page_info}&limit=5"
+    fake(
+      'orders',
+      method: :get,
+      status: 200,
+      api_version: @version,
+      url: "https://this-is-my-test-shop.myshopify.com/admin/api/unstable/orders.json?limit=10",
+      body: load_fixture('orders'),
+      link: "<https://this-is-my-test-shop.myshopify.com/admin/api/unstable/orders.json?#{second_request_params}>; rel=\"next\""
+    )
+
+    orders2 = ShopifyAPI::Order.where(limit: 10)
+
+    fake(
+      'orders',
+      method: :get,
+      status: 200,
+      api_version: @version,
+      url: "https://this-is-my-test-shop.myshopify.com/admin/api/unstable/orders.json?limit=5&page_info=#{@next_page_info}",
+      body: load_fixture('orders')
+    )
+    next_page = orders.fetch_next_page
+    assert_equal 450789469, next_page.first.id
+  end
+
 end