Add optional sentinel_value

Use fetch for sentinel_value

Use DateTime for sentinel_value example

Use an epoch. rails convers '0' or 0 to nil for datetime fields

Add test for restore

Update readme

Move MYSQL note to bottom of readme

update destroyed? for sentinel value

README.md

@@ -182,6 +182,27 @@ You can replace the older `acts_as_paranoid` methods as follows:
 The `recover` method in `acts_as_paranoid` runs `update` callbacks.  Paranoia's
 `restore` method does not do this.
 
+## Support for Unique Keys with Null Values
+
+Most databases ignore null columns when it comes to resolving unique index
+constraints.  This means unique constraints that involve nullable columns may be
+problematic. Instead of using `NULL` to represent a not-deleted row, you can pick
+a value that you want paranoia to mean not deleted. Note that you can/should
+now apply a `NOT NULL` constraint to your `deleted_at` column.
+
+Per model:
+
+```ruby
+# pick some value
+acts_as_paranoid sentinel_value: DateTime.new(0)
+```
+
+or globally in a rails initializer, e.g. `config/initializer/paranoia.rb`
+
+```ruby
+Paranoia.default_sentinel_value = DateTime.new(0)
+```
+
 ## License
 
 This gem is released under the MIT license.

lib/paranoia.rb

 require 'active_record' unless defined? ActiveRecord
 
 module Paranoia
+  @@default_sentinel_value = nil
+
+  # Change default_sentinel_value in a rails initilizer
+  def self.default_sentinel_value=(val)
+    @@default_sentinel_value = val
+  end
+
+  def self.default_sentinel_value
+    @@default_sentinel_value
+  end
+
   def self.included(klazz)
     klazz.extend Query
     klazz.extend Callbacks
@@ -18,7 +29,7 @@ module Paranoia
     end
 
     def only_deleted
-      with_deleted.where.not(paranoia_column => nil)
+      with_deleted.where.not(paranoia_column => paranoia_sentinel_value)
     end
     alias :deleted :only_deleted
 
@@ -76,7 +87,7 @@ module Paranoia
   def restore!(opts = {})
     self.class.transaction do
       run_callbacks(:restore) do
-        update_column paranoia_column, nil
+        update_column paranoia_column, paranoia_sentinel_value
         restore_associated_records if opts[:recursive]
       end
     end
@@ -84,7 +95,7 @@ module Paranoia
   alias :restore :restore!
 
   def destroyed?
-    !!send(paranoia_column)
+    send(paranoia_column) != paranoia_sentinel_value
   end
   alias :deleted? :destroyed?
 
@@ -155,10 +166,11 @@ class ActiveRecord::Base
     end
 
     include Paranoia
-    class_attribute :paranoia_column
+    class_attribute :paranoia_column, :paranoia_sentinel_value
 
     self.paranoia_column = options[:column] || :deleted_at
-    default_scope { where(paranoia_column => nil) }
+    self.paranoia_sentinel_value = options.fetch(:sentinel_value) { Paranoia.default_sentinel_value }
+    default_scope { where(paranoia_column => paranoia_sentinel_value) }
 
     before_restore {
       self.class.notify_observers(:before_restore, self) if self.class.respond_to?(:notify_observers)
@@ -194,6 +206,10 @@ class ActiveRecord::Base
   def paranoia_column
     self.class.paranoia_column
   end
+
+  def paranoia_sentinel_value
+    self.class.paranoia_sentinel_value
+  end
 end
 
 require 'paranoia/rspec' if defined? RSpec

test/paranoia_test.rb

@@ -24,6 +24,7 @@ def connect!
   ActiveRecord::Base.connection.execute 'CREATE TABLE employees (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME)'
   ActiveRecord::Base.connection.execute 'CREATE TABLE jobs (id INTEGER NOT NULL PRIMARY KEY, employer_id INTEGER NOT NULL, employee_id INTEGER NOT NULL, deleted_at DATETIME)'
   ActiveRecord::Base.connection.execute 'CREATE TABLE custom_column_models (id INTEGER NOT NULL PRIMARY KEY, destroyed_at DATETIME)'
+  ActiveRecord::Base.connection.execute 'CREATE TABLE custom_sentinel_models (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME NOT NULL)'
   ActiveRecord::Base.connection.execute 'CREATE TABLE non_paranoid_models (id INTEGER NOT NULL PRIMARY KEY, parent_model_id INTEGER)'
 end
 
@@ -158,6 +159,36 @@ class ParanoiaTest < test_framework
     assert_equal 1, model.class.deleted.count
   end
 
+  def test_default_sentinel_value
+    assert_equal nil, ParanoidModel.paranoia_sentinel_value
+  end
+
+  def test_sentinel_value_for_custom_sentinel_models
+    model = CustomSentinelModel.new
+    assert_equal 0, model.class.count
+    model.save!
+    assert_equal DateTime.new(0), model.deleted_at
+    assert_equal 1, model.class.count
+    model.destroy
+
+    assert DateTime.new(0) != model.deleted_at
+    assert model.destroyed?
+
+    assert_equal 0, model.class.count
+    assert_equal 1, model.class.unscoped.count
+    assert_equal 1, model.class.only_deleted.count
+    assert_equal 1, model.class.deleted.count
+
+    model.restore
+    assert_equal DateTime.new(0), model.deleted_at
+    assert !model.destroyed?
+
+    assert_equal 1, model.class.count
+    assert_equal 1, model.class.unscoped.count
+    assert_equal 0, model.class.only_deleted.count
+    assert_equal 0, model.class.deleted.count
+  end
+
   def test_destroy_behavior_for_featureful_paranoid_models
     model = get_featureful_model
     assert_equal 0, model.class.count
@@ -587,6 +618,10 @@ class CustomColumnModel < ActiveRecord::Base
   acts_as_paranoid column: :destroyed_at
 end
 
+class CustomSentinelModel < ActiveRecord::Base
+  acts_as_paranoid sentinel_value: DateTime.new(0)
+end
+
 class NonParanoidModel < ActiveRecord::Base
 end