Syntax for declaring resource paths in Grape - ruby

Question

I am looking for clarification on the syntax to declare API resource paths in Grape. The example below declares the resource paths "/items", "/items/:id", "/objects", and "/objects/:id". What I do not undestand is why the definition for "/items/:id" returns null?
class API < Grape::API
format :json
default_format :json
rescue_from :all, backtrace: true
resource :items do
desc "Returns an array of all items."
get do
ITEMS.find.to_a
end
desc "Returns an item by its id."
get '/:id' do
# hardcoding the document id returns the correct document
# ITEMS.find_one( "item_id" => 2519 )
# using the path parameter :id returns null, why???
ITEMS.find_one( "item_id" => params[:id] )
end
end
resource :objects do
desc "Returns an array of all objects."
get do
OBJECTS.find.to_a
end
##
# using the route_param syntax correctly returns the document
# resource path /objects/:id
##
desc "Returns an object by its id."
params do
requires :id, type: Integer
end
route_param :id do
get do
OBJECTS.find_one( "object_id" => params[:id] )
end
end
end
end

Answer 1

Your use of resource and route methods is ok.
You have a problem with parameter processing - params[:id] is a String by default. Your example hard-coded value that works is aFixnum (integer).
Probably your (not shown) code that queries the list on ITEMS is looking up integer values.
You could use ITEMS.find_one( "item_id" => params[:id].to_i ) to convert the param inline.
However, you probably should use a params description block to get Grape to convert for you, as you already are for OBJECTS:
desc "Returns an item by its id."
params do
requires :id, type: Integer
end
get '/:id' do
ITEMS.find_one( "item_id" => params[:id] )
end