Allow for alias omission in aggregate expressions

2 files changed, 44 insertions, 8 deletions

diff --git a/lib/arel/expressions.rb b/lib/arel/expressions.rb
index fa18f15b67..717cf412ee 100644
--- a/lib/arel/expressions.rb
+++ b/lib/arel/expressions.rb
@@ -4,24 +4,31 @@ module Arel
       Nodes::Count.new [self], distinct
     end
 
-    def sum
-      Nodes::Sum.new [self], Nodes::SqlLiteral.new('sum_id')
+    def sum(alias_as = "sum_id")
+      Nodes::Sum.new [self], node_alias(alias_as)
     end
 
-    def maximum
-      Nodes::Max.new [self], Nodes::SqlLiteral.new('max_id')
+    def maximum(alias_as = "max_id")
+      Nodes::Max.new [self], node_alias(alias_as)
     end
 
-    def minimum
-      Nodes::Min.new [self], Nodes::SqlLiteral.new('min_id')
+    def minimum(alias_as = "min_id")
+      Nodes::Min.new [self], node_alias(alias_as)
     end
 
-    def average
-      Nodes::Avg.new [self], Nodes::SqlLiteral.new('avg_id')
+    def average(alias_as = "avg_id")
+      Nodes::Avg.new [self], node_alias(alias_as)
     end
 
     def extract field
       Nodes::Extract.new [self], field
     end
+
+  private
+
+    def node_alias(alias_as)
+      alias_as.nil? ? nil : Nodes::SqlLiteral.new(alias_as)
+    end
+
   end
 end
diff --git a/test/test_expressions.rb b/test/test_expressions.rb
new file mode 100644
index 0000000000..d061bbc335
--- /dev/null
+++ b/test/test_expressions.rb
@@ -0,0 +1,29 @@
+require 'helper'
+
+module Arel
+  describe "Expressions" do
+    before do
+      @table = Table.new(:users)
+    end
+
+    describe "average" do
+      it "aliases the average as avg_id by default" do
+        @table[:score].average.to_sql.must_be_like %{
+          AVG("users"."score") AS avg_id
+        }
+      end
+
+      it "aliases the average as another string" do
+        @table[:score].average("my_alias").to_sql.must_be_like %{
+          AVG("users"."score") AS my_alias
+        }
+      end
+
+      it "omits the alias if nil" do
+        @table[:score].average(nil).to_sql.must_be_like %{
+          AVG("users"."score")
+        }
+      end
+    end
+  end
+end