(#8316) Ruby sorting for ResourceEvents.

While most of our sorting should go on in the database, there is a complex
"natural" order for ResourceEvents: the 'ensure' property comes first, then
everything else should be alphabetical.

Since the set of events for a resource_status is usually handled distinctly,
and is always small in that context, it can make sense to handle that at the
Ruby level.

It is also quite complex to push that logic down into the database, since SQL
does not easily express the logic required.

Reviewed-By: Pieter van de Bruggen <[email protected]>

app/models/resource_event.rb

@@ -1,7 +1,14 @@
-class ResourceEvent < ActiveRecord::Base    
+class ResourceEvent < ActiveRecord::Base
   belongs_to :resource_status
 
   serialize :desired_value
   serialize :previous_value
   serialize :historical_value
+
+  # The "natural" order of properties is that 'ensure' comes before anything
+  # else, then alphabetically sorted by the property name.
+  def <=>(that)
+    [self.property == 'ensure' ? 0 : 1, self.property] <=>
+      [that.property == 'ensure' ? 0 : 1, that.property]
+  end
 end

spec/models/resource_event_spec.rb

@@ -0,0 +1,20 @@
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
+
+describe ResourceEvent do
+  describe "#<=>" do
+    [%w{alpha ensure}, %w{zeta ensure}, %w{elfin ensure}].each do |input|
+      it "should sort ensure before anything else" do
+        input.map {|x| ResourceEvent.new(:property => x) }.
+          sort.map {|x| x.property }.should ==
+          ['ensure', input.first]
+      end
+    end
+
+    it "should sort anything else alphabetically" do
+      %w{elfin alpha ensure zeta equipage}.map do |x|
+        ResourceEvent.new(:property => x)
+      end.sort.map {|x| x.property }.should ==
+        %w{ensure alpha elfin equipage zeta}
+    end
+  end
+end