Merge pull request mongodb#2334 from jpmckinney/min

Bug when aggregating on field that doesn't always exist

lib/mongoid/contextual/aggregable/mongo.rb

@@ -167,10 +167,12 @@ def reducer
           function(key, values) {
             var agg = { count: 0, max: null, min: null, sum: 0 };
             values.forEach(function(val) {
-              if (agg.max == null || val.max > agg.max) agg.max = val.max;
-              if (agg.min == null || val.max < agg.min) agg.min = val.max;
+              if (val.max !== null) {
+                if (agg.max == null || val.max > agg.max) agg.max = val.max;
+                if (agg.min == null || val.max < agg.min) agg.min = val.max;
+                agg.sum += val.sum;
+              }
               agg.count += 1;
-              agg.sum += val.sum;
             });
             return agg;
           }}

spec/mongoid/contextual/aggregable/mongo_spec.rb

@@ -110,6 +110,56 @@
         end
       end
 
+      context "when the field sometimes exists" do
+        let!(:oasis) do
+          Band.create(name: "Oasis", likes: 50)
+        end
+
+        let!(:radiohead) do
+          Band.create(name: "Radiohead")
+        end
+
+        context "and the field doesn't exist on the last document" do
+          let(:criteria) do
+            Band.all
+          end
+
+          let(:context) do
+            Mongoid::Contextual::Mongo.new(criteria)
+          end
+
+          let(:aggregates) do
+            context.aggregates(:likes)
+          end
+
+          it "returns a min" do
+            aggregates["min"].should eq(50)
+          end
+        end
+
+        context "and the field doesn't exist on the before-last document" do
+          let!(:u2) do
+            Band.create(name: "U2", likes: 100)
+          end
+
+          let(:criteria) do
+            Band.all
+          end
+
+          let(:context) do
+            Mongoid::Contextual::Mongo.new(criteria)
+          end
+
+          let(:aggregates) do
+            context.aggregates(:likes)
+          end
+
+          it "returns a min" do
+            aggregates["min"].should eq(50)
+          end
+        end
+      end
+
       context "when there are no matching documents" do
 
         let(:criteria) do