I added this feature so that a Map of changed fields could be retrieved

after a model had been saved. This is useful in the after_save callback
when you need to know what fields changed. At present there is no way
to do this other than have code in the before_save callback that takes
a copy of the changes Map, which I thought was a bit messy.

Example.

  person = Person.find_by_name('bob')
  person.name = 'robert'
  person.changes # => {'name' => ['bob, 'robert']}
  person.save
  person.changes # => {}
  person.previous_changes # => {'name' => ['bob, 'robert']}
  person.reload
  person.previous_changes # => {}

Signed-off-by: Joshua Peek <josh@joshpeek.com>

1 files changed, 78 insertions, 0 deletions

diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index 74571d923a..f456d273fe 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -308,6 +308,84 @@ class DirtyTest < ActiveRecord::TestCase
     end
   end
 
+  def test_previous_changes
+    # original values should be in previous_changes
+    pirate = Pirate.new
+  
+    assert_equal Hash.new, pirate.previous_changes
+    pirate.catchphrase = "arrr"
+    pirate.save!
+  
+    assert_equal 4, pirate.previous_changes.size
+    assert_equal [nil, "arrr"], pirate.previous_changes['catchphrase']
+    assert_equal [nil, pirate.id], pirate.previous_changes['id']
+    assert_nil pirate.previous_changes['updated_on'][0]
+    assert_not_nil pirate.previous_changes['updated_on'][1]
+    assert_nil pirate.previous_changes['created_on'][0]
+    assert_not_nil pirate.previous_changes['created_on'][1]
+    assert !pirate.previous_changes.key?('parrot_id')
+  
+    # original values should be in previous_changes
+    pirate = Pirate.new
+  
+    assert_equal Hash.new, pirate.previous_changes
+    pirate.catchphrase = "arrr"
+    pirate.save
+  
+    assert_equal 4, pirate.previous_changes.size
+    assert_equal [nil, "arrr"], pirate.previous_changes['catchphrase']
+    assert_equal [nil, pirate.id], pirate.previous_changes['id']
+    assert pirate.previous_changes.include?('updated_on')
+    assert pirate.previous_changes.include?('created_on')
+    assert !pirate.previous_changes.key?('parrot_id')
+  
+    pirate.catchphrase = "Yar!!"
+    pirate.reload
+    assert_equal Hash.new, pirate.previous_changes
+
+    pirate = Pirate.find_by_catchphrase("arrr")
+    pirate.catchphrase = "Me Maties!"
+    pirate.save!
+
+    assert_equal 2, pirate.previous_changes.size
+    assert_equal ["arrr", "Me Maties!"], pirate.previous_changes['catchphrase']
+    assert_not_nil pirate.previous_changes['updated_on'][0]
+    assert_not_nil pirate.previous_changes['updated_on'][1]
+    assert !pirate.previous_changes.key?('parrot_id')
+    assert !pirate.previous_changes.key?('created_on')
+
+    pirate = Pirate.find_by_catchphrase("Me Maties!")
+    pirate.catchphrase = "Thar She Blows!"
+    pirate.save
+
+    assert_equal 2, pirate.previous_changes.size
+    assert_equal ["Me Maties!", "Thar She Blows!"], pirate.previous_changes['catchphrase']
+    assert_not_nil pirate.previous_changes['updated_on'][0]
+    assert_not_nil pirate.previous_changes['updated_on'][1]
+    assert !pirate.previous_changes.key?('parrot_id')
+    assert !pirate.previous_changes.key?('created_on')
+
+    pirate = Pirate.find_by_catchphrase("Thar She Blows!")
+    pirate.update_attributes(:catchphrase => "Ahoy!")
+
+    assert_equal 2, pirate.previous_changes.size
+    assert_equal ["Thar She Blows!", "Ahoy!"], pirate.previous_changes['catchphrase']
+    assert_not_nil pirate.previous_changes['updated_on'][0]
+    assert_not_nil pirate.previous_changes['updated_on'][1]
+    assert !pirate.previous_changes.key?('parrot_id')
+    assert !pirate.previous_changes.key?('created_on')
+
+    pirate = Pirate.find_by_catchphrase("Ahoy!")
+    pirate.update_attribute(:catchphrase, "Ninjas suck!")
+
+    assert_equal 2, pirate.previous_changes.size
+    assert_equal ["Ahoy!", "Ninjas suck!"], pirate.previous_changes['catchphrase']
+    assert_not_nil pirate.previous_changes['updated_on'][0]
+    assert_not_nil pirate.previous_changes['updated_on'][1]
+    assert !pirate.previous_changes.key?('parrot_id')
+    assert !pirate.previous_changes.key?('created_on')    
+  end
+
   private
     def with_partial_updates(klass, on = true)
       old = klass.partial_updates?