update_counters should update nil values.

This allows counter columns with default null instead of requiring default 0.

[#493 state:resolved]

activerecord/lib/active_record/base.rb

@@ -828,7 +828,7 @@ module ActiveRecord #:nodoc:
       def update_counters(id, counters)
         updates = counters.inject([]) { |list, (counter_name, increment)|
           sign = increment < 0 ? "-" : "+"
-          list << "#{connection.quote_column_name(counter_name)} = #{connection.quote_column_name(counter_name)} #{sign} #{increment.abs}"
+          list << "#{connection.quote_column_name(counter_name)} = COALESCE(#{connection.quote_column_name(counter_name)}, 0) #{sign} #{increment.abs}"
         }.join(", ")
         update_all(updates, "#{connection.quote_column_name(primary_key)} = #{quote_value(id)}")
       end

activerecord/test/cases/base_test.rb

@@ -19,6 +19,7 @@ require 'models/warehouse_thing'
 require 'rexml/document'
 
 class Category < ActiveRecord::Base; end
+class Categorization < ActiveRecord::Base; end
 class Smarts < ActiveRecord::Base; end
 class CreditCard < ActiveRecord::Base
   class PinNumber < ActiveRecord::Base
@@ -75,7 +76,7 @@ class TopicWithProtectedContentAndAccessibleAuthorName < ActiveRecord::Base
 end
 
 class BasicsTest < ActiveRecord::TestCase
-  fixtures :topics, :companies, :developers, :projects, :computers, :accounts, :minimalistics, 'warehouse-things', :authors
+  fixtures :topics, :companies, :developers, :projects, :computers, :accounts, :minimalistics, 'warehouse-things', :authors, :categorizations
 
   def test_table_exists
     assert !NonExistentTable.table_exists?
@@ -130,7 +131,7 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_read_attributes_before_type_cast
     category = Category.new({:name=>"Test categoty", :type => nil})
-    category_attrs = {"name"=>"Test categoty", "type" => nil}
+    category_attrs = {"name"=>"Test categoty", "type" => nil, "categorizations_count" => nil}
     assert_equal category_attrs , category.attributes_before_type_cast
   end
 
@@ -614,6 +615,22 @@ class BasicsTest < ActiveRecord::TestCase
     assert_equal -2, Topic.find(2).replies_count
   end
 
+  def test_update_counter
+    category = Category.first
+    assert_nil category.categorizations_count
+    assert_equal 2, category.categorizations.count
+
+    Category.update_counters(category.id, "categorizations_count" => category.categorizations.count)
+    category.reload
+    assert_not_nil category.categorizations_count
+    assert_equal 2, category.categorizations_count
+
+    Category.update_counters(category.id, "categorizations_count" => category.categorizations.count)
+    category.reload
+    assert_not_nil category.categorizations_count
+    assert_equal 4, category.categorizations_count
+  end
+
   def test_update_all
     assert_equal Topic.count, Topic.update_all("content = 'bulk updated!'")
     assert_equal "bulk updated!", Topic.find(1).content

activerecord/test/schema/schema.rb

@@ -66,6 +66,7 @@ ActiveRecord::Schema.define do
   create_table :categories, :force => true do |t|
     t.string :name, :null => false
     t.string :type
+    t.integer :categorizations_count
   end
 
   create_table :categories_posts, :force => true, :id => false do |t|