Save Calculations as Instance Variables

In order to lighten the load on the DB when using Metric Objects we now
calculate the values when it is initialized.

lib/totalizer/metric.rb

@@ -3,6 +3,7 @@ class Metric
     def initialize params
       @params = params
       validate!
+      calculate!
     end
 
     def change
@@ -22,7 +23,7 @@ def filter
     end
 
     def ids
-      calculate
+      @ids
     end
 
     def map
@@ -34,7 +35,7 @@ def model
     end
 
     def previous_ids
-      calculate(2)
+      @previous_ids
     end
 
     def previous_value
@@ -59,6 +60,11 @@ def build_date_range duration_multiplier
       start_date - (duration * duration_multiplier).days..start_date - (duration * (duration_multiplier - 1)).days
     end
 
+    def calculate!
+      @ids = calculate
+      @previous_ids = calculate(2)
+    end
+
     def calculate duration_multiplier=1
       model.where(filter).where(created_at: build_date_range(duration_multiplier)).map { |object| object.send(map) }.uniq
     end

spec/lib/totalizer/metric_spec.rb

@@ -7,8 +7,7 @@
     end
 
     it "requires a valid filter" do
-      metric = Totalizer::Metric.new({ model: User, start_date: Date.today, duration: 7, filter: 'non_existant_field = true' })
-      expect{metric.calculate}.to raise_exception
+      expect{ Totalizer::Metric.new({ model: User, start_date: Date.today, duration: 7, filter: 'non_existant_field = true' }) }.to raise_exception
     end
   end