Froze rails gems

[depot.git] / vendor / rails / activerecord / lib / active_record / locking / optimistic.rb

diff --git a/vendor/rails/activerecord/lib/active_record/locking/optimistic.rb b/vendor/rails/activerecord/lib/active_record/locking/optimistic.rb
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+++ b/vendor/rails/activerecord/lib/active_record/locking/optimistic.rb
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+module ActiveRecord
+  module Locking
+    # == What is Optimistic Locking
+    #
+    # Optimistic locking allows multiple users to access the same record for edits, and assumes a minimum of
+    # conflicts with the data.  It does this by checking whether another process has made changes to a record since
+    # it was opened, an ActiveRecord::StaleObjectError is thrown if that has occurred and the update is ignored.
+    #
+    # Check out ActiveRecord::Locking::Pessimistic for an alternative.
+    #
+    # == Usage
+    #
+    # 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>.
+    # To override the name of the lock_version column, invoke the <tt>set_locking_column</tt> method.
+    # This method uses the same syntax as <tt>set_table_name</tt>
+    module Optimistic
+      def self.included(base) #:nodoc:
+        base.extend ClassMethods
+
+        base.cattr_accessor :lock_optimistically, :instance_writer => false
+        base.lock_optimistically = true
+
+        base.alias_method_chain :update, :lock
+        base.alias_method_chain :attributes_from_column_definition, :lock
+
+        class << base
+          alias_method :locking_column=, :set_locking_column
+        end
+      end
+
+      def locking_enabled? #:nodoc:
+        self.class.locking_enabled?
+      end
+
+      private
+        def attributes_from_column_definition_with_lock
+          result = attributes_from_column_definition_without_lock
+
+          # If the locking column has no default value set,
+          # start the lock version at zero.  Note we can't use
+          # locking_enabled? at this point as @attributes may
+          # not have been initialized yet
+
+          if lock_optimistically && result.include?(self.class.locking_column)
+            result[self.class.locking_column] ||= 0
+          end
+
+          return result
+        end
+
+        def update_with_lock(attribute_names = @attributes.keys) #:nodoc:
+          return update_without_lock(attribute_names) unless locking_enabled?
+          return 0 if attribute_names.empty?
+
+          lock_col = self.class.locking_column
+          previous_value = send(lock_col).to_i
+          send(lock_col + '=', previous_value + 1)
+
+          attribute_names += [lock_col]
+          attribute_names.uniq!
+
+          begin
+            affected_rows = connection.update(<<-end_sql, "#{self.class.name} Update with optimistic locking")
+              UPDATE #{self.class.quoted_table_name}
+              SET #{quoted_comma_pair_list(connection, attributes_with_quotes(false, false, attribute_names))}
+              WHERE #{self.class.primary_key} = #{quote_value(id)}
+              AND #{self.class.quoted_locking_column} = #{quote_value(previous_value)}
+            end_sql
+
+            unless affected_rows == 1
+              raise ActiveRecord::StaleObjectError, "Attempted to update a stale object"
+            end
+
+            affected_rows
+
+          # If something went wrong, revert the version.
+          rescue Exception
+            send(lock_col + '=', previous_value)
+            raise
+          end
+        end
+
+      module ClassMethods
+        DEFAULT_LOCKING_COLUMN = 'lock_version'
+
+        def self.extended(base)
+          class <<base
+            alias_method_chain :update_counters, :lock
+          end
+        end
+
+        # Is optimistic locking enabled for this table? Returns true if the
+        # +lock_optimistically+ flag is set to true (which it is, by default)
+        # and the table includes the +locking_column+ column (defaults to
+        # +lock_version+).
+        def locking_enabled?
+          lock_optimistically && columns_hash[locking_column]
+        end
+
+        # Set the column to use for optimistic locking. Defaults to +lock_version+.
+        def set_locking_column(value = nil, &block)
+          define_attr_method :locking_column, value, &block
+          value
+        end
+
+        # The version column used for optimistic locking. Defaults to +lock_version+.
+        def locking_column
+          reset_locking_column
+        end
+
+        # Quote the column name used for optimistic locking.
+        def quoted_locking_column
+          connection.quote_column_name(locking_column)
+        end
+
+        # Reset the column used for optimistic locking back to the +lock_version+ default.
+        def reset_locking_column
+          set_locking_column DEFAULT_LOCKING_COLUMN
+        end
+
+        # Make sure the lock version column gets updated when counters are
+        # updated.
+        def update_counters_with_lock(id, counters)
+          counters = counters.merge(locking_column => 1) if locking_enabled?
+          update_counters_without_lock(id, counters)
+        end
+      end
+    end
+  end
+end