Fixed a problem where sum, size, average, minimum and maximum used

with a grouping was not returning a Hash.

activerecord/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Fixed a problem where `sum`, `size`, `average`, `minimum` and `maximum`
+    used with a grouping was not returning a Hash.
+
+    *Kuldeep Aggarwal*
+
 *   Fix `stored_attributes` to correctly merge the details of stored
     attributes defined in parent classes.
 

activerecord/lib/active_record/null_relation.rb

@@ -23,7 +23,7 @@ module ActiveRecord
     end
 
     def size
-      0
+      calculate :size, nil
     end
 
     def empty?
@@ -47,14 +47,28 @@ module ActiveRecord
     end
 
     def sum(*)
-      0
+      calculate :sum, nil
+    end
+
+    def average(*)
+      calculate :average, nil
+    end
+
+    def minimum(*)
+      calculate :minimum, nil
+    end
+
+    def maximum(*)
+      calculate :maximum, nil
     end
 
     def calculate(operation, _column_name, _options = {})
       # TODO: Remove _options argument as soon we remove support to
       # activerecord-deprecated_finders.
-      if operation == :count
+      if [:count, :sum, :size].include? operation
         group_values.any? ? Hash.new : 0
+      elsif [:average, :minimum, :maximum].include?(operation) && group_values.any?
+        Hash.new
       else
         nil
       end

activerecord/test/cases/relations_test.rb

@@ -366,6 +366,14 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal({ 'salary' => 100_000 }, Developer.none.where(salary: 100_000).where_values_hash)
   end
 
+  def test_null_relation_sum
+    ac = Aircraft.new
+    assert_equal Hash.new, ac.engines.group(:id).sum(:id)
+    assert_equal        0, ac.engines.count
+    ac.save
+    assert_equal Hash.new, ac.engines.group(:id).sum(:id)
+    assert_equal        0, ac.engines.count
+  end
 
   def test_null_relation_count
     ac = Aircraft.new
@@ -376,6 +384,42 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal        0, ac.engines.count
   end
 
+  def test_null_relation_size
+    ac = Aircraft.new
+    assert_equal Hash.new, ac.engines.group(:id).size
+    assert_equal        0, ac.engines.size
+    ac.save
+    assert_equal Hash.new, ac.engines.group(:id).size
+    assert_equal        0, ac.engines.size
+  end
+
+  def test_null_relation_average
+    ac = Aircraft.new
+    assert_equal Hash.new, ac.engines.group(:car_id).average(:id)
+    assert_equal        nil, ac.engines.average(:id)
+    ac.save
+    assert_equal Hash.new, ac.engines.group(:car_id).average(:id)
+    assert_equal        nil, ac.engines.average(:id)
+  end
+
+  def test_null_relation_minimum
+    ac = Aircraft.new
+    assert_equal Hash.new, ac.engines.group(:car_id).minimum(:id)
+    assert_equal        nil, ac.engines.minimum(:id)
+    ac.save
+    assert_equal Hash.new, ac.engines.group(:car_id).minimum(:id)
+    assert_equal        nil, ac.engines.minimum(:id)
+  end
+
+  def test_null_relation_maximum
+    ac = Aircraft.new
+    assert_equal Hash.new, ac.engines.group(:car_id).maximum(:id)
+    assert_equal        nil, ac.engines.maximum(:id)
+    ac.save
+    assert_equal Hash.new, ac.engines.group(:car_id).maximum(:id)
+    assert_equal        nil, ac.engines.maximum(:id)
+  end
+
   def test_joins_with_nil_argument
     assert_nothing_raised { DependentFirm.joins(nil).first }
   end