option column for flagging deletes allowing unique keys to work properly

Fixes #138

README.md

@@ -178,6 +178,44 @@ You can replace the older `acts_as_paranoid` methods as follows:
 |`find_with_deleted(:first)` | `Client.with_deleted.first`    |
 |`find_with_deleted(id)`     | `Client.with_deleted.find(id)` |
 
+## Support for Unique Keys with Null Values
+
+With most databases, a unique key containing a null value will not be enforced because the null value is unique per row.
+
+``` ruby
+class AddDeletedAtToClients < ActiveRecord::Migration
+  def change
+    add_column :clients, :deleted_at, :datetime
+    add_index :clients, [:username, :deleted_at], unique: true
+  end
+end
+```
+
+Given the migration above, you could have multiple users with username bob given the following inserts: ('bob', null), ('bob', null), ('bob', null). We can agree this is not the expected behavior.
+
+To avoid this problem, we could use a flag column instead of a datetime, but the datetime value has intrinsic usefulness.  Instead, we can add a second column for the unique key that always has a value, in this case 0 or 1:
+
+``` ruby
+class AddDeletedAtToClients < ActiveRecord::Migration
+  def change
+    add_column :clients, :deleted_at, :datetime
+    add_column :clients, :is_deleted, :boolean, null: false, default: 0
+    add_index :clients, [:username, :is_deleted], unique: true
+  end
+end
+```
+
+Support this new column by updating your model as such:
+
+``` ruby
+class Client < ActiveRecord::Base
+  acts_as_paranoid :flag_column => :is_deleted
+  ...
+end
+```
+
+If you create an index on the flag column, and you want paranoia to use that index instead of deleted_at, you can add `:index_column => :is_deleted` to the acts_as_paranoid definition.
+
 ## License
 
 This gem is released under the MIT license.

lib/paranoia.rb

@@ -11,14 +11,14 @@ module Paranoia
 
     def with_deleted
       if ActiveRecord::VERSION::STRING >= "4.1"
-        unscope where: paranoia_column
+        unscope where: paranoia_indexed_column
       else
         all.tap { |x| x.default_scoped = false }
       end
     end
 
     def only_deleted
-      with_deleted.where.not(paranoia_column => nil)
+      with_deleted.where.not(paranoia_indexed_column => paranoia_false_value)
     end
     alias :deleted :only_deleted
 
@@ -29,6 +29,12 @@ module Paranoia
         only_deleted.find(id).restore!(opts)
       end
     end
+
+    private
+
+    def paranoia_false_value
+      (paranoia_indexed_column == paranoia_column) ? nil : 0
+    end
   end
 
   module Callbacks
@@ -73,6 +79,7 @@ module Paranoia
     ActiveRecord::Base.transaction do
       run_callbacks(:restore) do
         update_column paranoia_column, nil
+        update_column(paranoia_flag_column, false) if paranoia_flag_column
         restore_associated_records if opts[:recursive]
       end
     end
@@ -86,7 +93,12 @@ module Paranoia
 
   private
 
-  # touch paranoia column.
+  def mark_columns_deleted
+    update_column(paranoia_flag_column, true) if paranoia_flag_column
+    touch(paranoia_column)
+  end
+
+  # touch paranoia column, update flag column if necessary
   # insert time to paranoia column.
   # @param with_transaction [Boolean] exec with ActiveRecord Transactions.
   def touch_paranoia_column(with_transaction=false)
@@ -95,9 +107,11 @@ module Paranoia
     # Let's not touch it if it's frozen.
     unless self.frozen?
       if with_transaction
-        with_transaction_returning_status { touch(paranoia_column) }
+        with_transaction_returning_status do
+          mark_columns_deleted
+        end
       else
-        touch(paranoia_column)
+        mark_columns_deleted
       end
     end
   end
@@ -146,9 +160,13 @@ class ActiveRecord::Base
 
     include Paranoia
     class_attribute :paranoia_column
+    class_attribute :paranoia_flag_column
+    class_attribute :paranoia_indexed_column
 
     self.paranoia_column = options[:column] || :deleted_at
-    default_scope { where(paranoia_column => nil) }
+    self.paranoia_flag_column = options[:flag_column] || nil
+    self.paranoia_indexed_column = options[:indexed_column] || paranoia_column
+    default_scope { where(paranoia_indexed_column => paranoia_false_value) }
 
     before_restore {
       self.class.notify_observers(:before_restore, self) if self.class.respond_to?(:notify_observers)
@@ -181,6 +199,14 @@ class ActiveRecord::Base
 
   private
 
+  def paranoia_flag_column
+    self.class.paranoia_flag_column
+  end
+
+  def paranoia_indexed_column
+    self.class.paranoia_indexed_column
+  end
+
   def paranoia_column
     self.class.paranoia_column
   end

test/paranoia_test.rb

@@ -14,7 +14,7 @@ ActiveRecord::Base.connection.execute 'CREATE TABLE parent_models (id INTEGER NO
 ActiveRecord::Base.connection.execute 'CREATE TABLE paranoid_models (id INTEGER NOT NULL PRIMARY KEY, parent_model_id INTEGER, deleted_at DATETIME)'
 ActiveRecord::Base.connection.execute 'CREATE TABLE paranoid_model_with_belongs (id INTEGER NOT NULL PRIMARY KEY, parent_model_id INTEGER, deleted_at DATETIME, paranoid_model_with_has_one_id INTEGER)'
 ActiveRecord::Base.connection.execute 'CREATE TABLE featureful_models (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME, name VARCHAR(32))'
-ActiveRecord::Base.connection.execute 'CREATE TABLE plain_models (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME)'
+ActiveRecord::Base.connection.execute 'CREATE TABLE plain_models (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME, is_deleted tinyint(1) not null default 0)'
 ActiveRecord::Base.connection.execute 'CREATE TABLE callback_models (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME)'
 ActiveRecord::Base.connection.execute 'CREATE TABLE fail_callback_models (id INTEGER NOT NULL PRIMARY KEY, deleted_at DATETIME)'
 ActiveRecord::Base.connection.execute 'CREATE TABLE related_models (id INTEGER NOT NULL PRIMARY KEY, parent_model_id INTEGER NOT NULL, deleted_at DATETIME)'
@@ -442,6 +442,32 @@ class ParanoiaTest < test_framework
     # essentially, we're just ensuring that this doesn't crash
   end
 
+  def test_destroy_flagged_model
+    a = FlaggedModel.create
+    assert_equal false, a.is_deleted?
+
+    a.destroy
+    assert_equal true, a.is_deleted?
+  end
+
+  def test_restore_flagged_model
+    a = FlaggedModel.create
+    a.destroy
+    a.restore!
+    assert_equal false, a.is_deleted?
+    assert_equal false, a.deleted?
+  end
+
+  def test_uses_flagged_index
+    a = FlaggedModelWithCustomIndex.create(is_deleted: 0)
+    assert_equal 1, FlaggedModelWithCustomIndex.count
+    a.destroy
+    assert_equal 0, FlaggedModelWithCustomIndex.count
+    assert FlaggedModelWithCustomIndex.all.to_sql.index(FlaggedModelWithCustomIndex.paranoia_indexed_column.to_s)
+    assert !FlaggedModelWithCustomIndex.all.to_sql.index( FlaggedModelWithCustomIndex.paranoia_column.to_s)
+  end
+
+
   def test_i_am_the_destroyer
     output = capture(:stdout) { ParanoidModel.I_AM_THE_DESTROYER! }
     assert_equal %Q{
@@ -557,3 +583,11 @@ class ParanoidModelWithBelong < ActiveRecord::Base
   acts_as_paranoid
   belongs_to :paranoid_model_with_has_one
 end
+
+class FlaggedModel < PlainModel
+  acts_as_paranoid :flag_column => :is_deleted
+end
+
+class FlaggedModelWithCustomIndex < PlainModel
+  acts_as_paranoid :flag_column => :is_deleted, :indexed_column => :is_deleted
+end