Added automated optimistic locking if the field lock_version is present #384 [Michael Koziarski]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@295 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

11 files changed, 143 insertions, 3 deletions

diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index b97085cdba..8a0d75ee8a 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,23 @@
 *SVN*
 
+* Added automated optimistic locking if the field <tt>lock_version</tt> is present.  Each update to the
+  record increments the lock_version column and the locking facilities ensure that records instantiated twice
+  will let the last one saved raise a StaleObjectError if the first was also updated. Example:
+  
+    p1 = Person.find(1)
+    p2 = Person.find(1)
+    
+    p1.first_name = "Michael"
+    p1.save
+    
+    p2.first_name = "should fail"
+    p2.save # Raises a ActiveRecord::StaleObjectError
+  
+  You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging,
+  or otherwise apply the business logic needed to resolve the conflict.
+
+  #384 [Michael Koziarski]
+
 * Added :counter_cache option to acts_as_tree that works just like the one you can define on belongs_to #371 [Josh]
 
 * Fixed quoting in validates_format_of that would allow some rules to pass regardless of input #390 [Dmitry V. Sabanin]
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index ecf8499e16..963a14dd3e 100755
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -39,11 +39,13 @@ require 'active_record/reflection'
 require 'active_record/timestamp'
 require 'active_record/acts/list'
 require 'active_record/acts/tree'
+require 'active_record/locking'
 
 ActiveRecord::Base.class_eval do
   include ActiveRecord::Validations
-  include ActiveRecord::Timestamp
   include ActiveRecord::Callbacks
+  include ActiveRecord::Locking
+  include ActiveRecord::Timestamp
   include ActiveRecord::Associations
   include ActiveRecord::Aggregations
   include ActiveRecord::Transactions
@@ -55,4 +57,4 @@ end
 require 'active_record/connection_adapters/mysql_adapter'
 require 'active_record/connection_adapters/postgresql_adapter'
 require 'active_record/connection_adapters/sqlite_adapter'
-require 'active_record/connection_adapters/sqlserver_adapter'
\ No newline at end of file
+require 'active_record/connection_adapters/sqlserver_adapter'
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index e4283ac157..849fb1578b 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -26,6 +26,8 @@ module ActiveRecord #:nodoc:
   end
   class PreparedStatementInvalid < ActiveRecordError #:nodoc:
   end
+  class StaleObjectError < ActiveRecordError #:nodoc:
+  end
 
   # Active Record objects doesn't specify their attributes directly, but rather infer them from the table definition with
   # which they're linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change
diff --git a/activerecord/lib/active_record/locking.rb b/activerecord/lib/active_record/locking.rb
new file mode 100644
index 0000000000..e08e2fcec8
--- /dev/null
+++ b/activerecord/lib/active_record/locking.rb
@@ -0,0 +1,57 @@
+module ActiveRecord
+  module Locking
+    # Active Records support optimistic locking if the field <tt>lock_version</tt> is present.  Each update to the
+    # record increments the lock_version column and the locking facilities ensure that records instantiated twice
+    # will let the last one saved raise a StaleObjectError if the first was also updated. Example:
+    #
+    #   p1 = Person.find(1)
+    #   p2 = Person.find(1)
+    #   
+    #   p1.first_name = "Michael"
+    #   p1.save
+    #   
+    #   p2.first_name = "should fail"
+    #   p2.save # Raises a ActiveRecord::StaleObjectError
+    #
+    # You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging,
+    # or otherwise apply the business logic needed to resolve the conflict.
+    #
+    # You must ensure that your database schema defaults the lock_version column to 0.
+    #
+    # This behavior can be turned off by setting <tt>ActiveRecord::Base.lock_optimistically = false</tt>.
+    def self.append_features(base)
+      super
+      base.class_eval do
+        alias_method :update_without_lock, :update
+        alias_method :update, :update_with_lock
+      end
+    end
+
+    def update_with_lock
+      if locking_enabled?
+        previous_value    = self.lock_version
+        self.lock_version = previous_value + 1
+        
+        affected_rows = connection.update(
+          "UPDATE #{self.class.table_name} "+
+          "SET #{quoted_comma_pair_list(connection, attributes_with_quotes(false))} " +
+          "WHERE #{self.class.primary_key} = #{quote(id)} AND lock_version = #{quote(previous_value)}",
+          "#{self.class.name} Update with optimistic locking"
+        )
+        
+        raise(ActiveRecord::StaleObjectError, "Attempted to update a stale object") unless affected_rows == 1
+      else
+        update_without_lock
+      end
+    end
+  end
+
+  class Base
+    @@lock_optimistically = true
+    cattr_accessor :lock_optimistically
+
+    def locking_enabled?
+      lock_optimistically && respond_to?(:lock_version)
+    end
+  end
+end
\ No newline at end of file
diff --git a/activerecord/test/fixtures/db_definitions/mysql.sql b/activerecord/test/fixtures/db_definitions/mysql.sql
index 7bd06e6243..ec27a52445 100755
--- a/activerecord/test/fixtures/db_definitions/mysql.sql
+++ b/activerecord/test/fixtures/db_definitions/mysql.sql
@@ -110,3 +110,9 @@ CREATE TABLE `mixins` (
   `type` varchar(40) default NULL,
   PRIMARY KEY  (`id`)
 );
+
+CREATE TABLE `people` (
+  `id` INTEGER NOT NULL PRIMARY KEY,
+  `first_name` VARCHAR(40) NOT NULL,
+  `lock_version` INTEGER NOT NULL DEFAULT 0
+);
\ No newline at end of file
diff --git a/activerecord/test/fixtures/db_definitions/postgresql.sql b/activerecord/test/fixtures/db_definitions/postgresql.sql
index 305852ba7f..6d8222cfd6 100644
--- a/activerecord/test/fixtures/db_definitions/postgresql.sql
+++ b/activerecord/test/fixtures/db_definitions/postgresql.sql
@@ -127,3 +127,10 @@ CREATE TABLE mixins (
   updated_at timestamp,
   PRIMARY KEY  (id)
 );
+
+CREATE TABLE people (
+  id serial,
+  first_name text,
+  lock_version integer default 0,
+  PRIMARY KEY  (id)
+);
\ No newline at end of file
diff --git a/activerecord/test/fixtures/db_definitions/sqlite.sql b/activerecord/test/fixtures/db_definitions/sqlite.sql
index 9bab9d9a15..5c27832056 100644
--- a/activerecord/test/fixtures/db_definitions/sqlite.sql
+++ b/activerecord/test/fixtures/db_definitions/sqlite.sql
@@ -99,4 +99,8 @@ CREATE TABLE 'mixins' (
   'updated_at' DATETIME DEFAULT NULL
 );
 
-
+CREATE TABLE 'people' (
+  'id' INTEGER NOT NULL PRIMARY KEY,
+  'first_name' VARCHAR(40) DEFAULT NULL,
+  'lock_version' INTEGER NOT NULL DEFAULT 0
+);
\ No newline at end of file
diff --git a/activerecord/test/fixtures/db_definitions/sqlserver.sql b/activerecord/test/fixtures/db_definitions/sqlserver.sql
index 4152ef59cb..74cd381ba3 100644
--- a/activerecord/test/fixtures/db_definitions/sqlserver.sql
+++ b/activerecord/test/fixtures/db_definitions/sqlserver.sql
@@ -110,3 +110,9 @@ CREATE TABLE mixins (
 );
 
 
+CREATE TABLE people (
+  id int NOT NULL IDENTITY(1, 1),
+  first_name varchar(40) NULL,
+  lock_version int default 0,
+  PRIMARY KEY (id)
+);
\ No newline at end of file
diff --git a/activerecord/test/fixtures/people.yml b/activerecord/test/fixtures/people.yml
new file mode 100644
index 0000000000..22c64afb70
--- /dev/null
+++ b/activerecord/test/fixtures/people.yml
@@ -0,0 +1,3 @@
+michael:
+  id: 1
+  first_name: Michael
\ No newline at end of file
diff --git a/activerecord/test/fixtures/person.rb b/activerecord/test/fixtures/person.rb
new file mode 100644
index 0000000000..4fa5811c71
--- /dev/null
+++ b/activerecord/test/fixtures/person.rb
@@ -0,0 +1 @@
+class Person < ActiveRecord::Base; end
diff --git a/activerecord/test/locking_test.rb b/activerecord/test/locking_test.rb
new file mode 100644
index 0000000000..2b77a29907
--- /dev/null
+++ b/activerecord/test/locking_test.rb
@@ -0,0 +1,34 @@
+require 'abstract_unit'
+require 'fixtures/person'
+
+class LockingTest < Test::Unit::TestCase
+  def setup
+    @people = create_fixtures('people')
+  end
+
+  def test_lock_existing
+    p1 = Person.find(1)
+    p2 = Person.find(1)
+    
+    p1.first_name = "Michael"
+    p1.save
+    
+    assert_raises(ActiveRecord::StaleObjectError) {
+      p2.first_name = "should fail"
+      p2.save
+    }
+  end
+
+  def test_lock_new
+    p1 = Person.create({ "first_name"=>"anika"})
+    p2 = Person.find(p1.id)
+    assert_equal p1.id, p2.id
+    p1.first_name = "Anika"
+    p1.save
+    
+    assert_raises(ActiveRecord::StaleObjectError) {
+      p2.first_name = "should fail"
+      p2.save
+    }
+  end 
+end
\ No newline at end of file