activerecord: reuse immutable objects

4 files changed, 20 insertions, 14 deletions

diff --git a/activerecord/lib/active_record/relation/from_clause.rb b/activerecord/lib/active_record/relation/from_clause.rb
index 92340216ed..8945cb0cc5 100644
--- a/activerecord/lib/active_record/relation/from_clause.rb
+++ b/activerecord/lib/active_record/relation/from_clause.rb
@@ -25,7 +25,7 @@ module ActiveRecord
       end
 
       def self.empty
-        new(nil, nil)
+        @empty ||= new(nil, nil)
       end
     end
   end
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index b86cc094fc..5635b4215b 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -54,16 +54,17 @@ module ActiveRecord
       end
     end
 
+    FROZEN_EMPTY_ARRAY = [].freeze
     Relation::MULTI_VALUE_METHODS.each do |name|
       class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_values                    # def select_values
-          @values[:#{name}] || []             #   @values[:select] || []
-        end                                   # end
-                                              #
-        def #{name}_values=(values)           # def select_values=(values)
-          assert_mutability!                  #   assert_mutability!
-          @values[:#{name}] = values          #   @values[:select] = values
-        end                                   # end
+        def #{name}_values
+          @values[:#{name}] || FROZEN_EMPTY_ARRAY
+        end
+
+        def #{name}_values=(values)
+          assert_mutability!
+          @values[:#{name}] = values
+        end
       CODE
     end
 
@@ -116,8 +117,9 @@ module ActiveRecord
       result
     end
 
+    FROZEN_EMPTY_HASH = {}.freeze
     def create_with_value # :nodoc:
-      @values[:create_with] || {}
+      @values[:create_with] || FROZEN_EMPTY_HASH
     end
 
     alias extensions extending_values
@@ -1190,7 +1192,7 @@ module ActiveRecord
     def structurally_compatible_for_or?(other)
       Relation::SINGLE_VALUE_METHODS.all? { |m| send("#{m}_value") == other.send("#{m}_value") } &&
         (Relation::MULTI_VALUE_METHODS - [:extending]).all? { |m| send("#{m}_values") == other.send("#{m}_values") } &&
-        (Relation::CLAUSE_METHODS - [:having, :where]).all? { |m| send("#{m}_clause") != other.send("#{m}_clause") }
+        (Relation::CLAUSE_METHODS - [:having, :where]).all? { |m| send("#{m}_clause") == other.send("#{m}_clause") }
     end
 
     def new_where_clause
diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
index 1f000b3f0f..2c2d6cfa47 100644
--- a/activerecord/lib/active_record/relation/where_clause.rb
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -81,7 +81,7 @@ module ActiveRecord
       end
 
       def self.empty
-        new([], [])
+        @empty ||= new([], [])
       end
 
       protected
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index 2f0382e273..03583344a8 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -43,13 +43,17 @@ module ActiveRecord
       (Relation::SINGLE_VALUE_METHODS - [:create_with]).each do |method|
         assert_nil relation.send("#{method}_value"), method.to_s
       end
-      assert_equal({}, relation.create_with_value)
+      value = relation.create_with_value
+      assert_equal({}, value)
+      assert_predicate value, :frozen?
     end
 
     def test_multi_value_initialize
       relation = Relation.new(FakeKlass, :b, nil)
       Relation::MULTI_VALUE_METHODS.each do |method|
-        assert_equal [], relation.send("#{method}_values"), method.to_s
+        values = relation.send("#{method}_values")
+        assert_equal [], values, method.to_s
+        assert_predicate values, :frozen?, method.to_s
       end
     end