Add include_for_find support via 'expand'

Allows for opt in of `:include_for_find` option for `Rbac::Filterer` via
the `expand` request parameter.

Include for find will effectively add a `.include` to the base query
done in `collection_search`, which in cases like this:

    /api/vms?expand=resources,hardware&attributes=num_cpu,name

Can avoid an N+1 on the associated resource.

Author: NickLaMuro

app/controllers/api/base_controller/parameters.rb

@@ -100,6 +100,16 @@ def sort_directive(klass, attr, order, options)
         end
         arel
       end
+
+      def determine_include_for_find(klass)
+        return nil unless klass.respond_to?(:reflect_on_association)
+
+        relations = @req.derived_include_for_find.select do |relation|
+                      klass.reflect_on_association(relation)
+                    end
+
+        relations.empty? ? nil : relations
+      end
     end
   end
 end

app/controllers/api/base_controller/renderer.rb

@@ -185,6 +185,7 @@ def collection_filterer(res, type, klass, is_subcollection = false)
         options[:filter] = miq_expression if miq_expression
         options[:offset] = params['offset'] if params['offset']
         options[:limit] = params['limit'] if params['limit']
+        options[:include_for_find] = determine_include_for_find(klass)
 
         filter_results(miq_expression, res, options)
       end

lib/api/request_adapter.rb

@@ -37,6 +37,10 @@ def attributes
       @attributes ||= @params['attributes'].to_s.split(',')
     end
 
+    def derived_include_for_find
+      @derived_include_for_find ||= expand_requested.reject { |item| item == "resource" }
+    end
+
     def base
       url.partition(fullpath)[0] # http://target
     end

spec/requests/vms_spec.rb

@@ -82,6 +82,11 @@ def update_raw_power_state(state, *vms)
                                    [{"vendor" => "openstack"},
                                     {"vendor" => "openstack"}])
     end
+
+    include_examples "for 'expand' query optimizations" do
+      let!(:includes)   { "hardware" }
+      let!(:attributes) { "num_cpu,name" }
+    end
   end
 
   context 'Vm edit' do

spec/support/shared_examples/expand_resources_includes.rb

@@ -0,0 +1,29 @@
+RSpec.shared_context "for 'expand' query optimizations" do
+  context "expand attribute query optimizations" do
+    let(:resource)  { :vms }
+    let(:index_url) { api_vms_url }
+
+    it "removes N+1's from the index query for subcollections/virtual_attributes" do
+      api_basic_authorize action_identifier(resource, :read, :resource_actions, :get)
+
+      expands    = ["resources"]
+      from_match = [resource]
+
+      if defined?(includes)
+        expands    << includes
+        from_match << includes
+      end
+
+      attrs                = defined?(attributes)  ? attributes  : "resources"
+      query_match          = /SELECT.*FROM\s"(?:#{from_match.join("|")})"/m
+      expected_query_count = defined?(query_count) ? query_count : 10
+
+      expect {
+        get index_url, :params => {
+          :expand     => expands.join(','),
+          :attributes => attrs
+        }
+      }.to make_database_queries(:count => expected_query_count, :matching => query_match)
+    end
+  end
+end