root/lang/ruby/pritter/vendor/rails/activerecord/lib/active_record/locking/optimistic.rb @ 5644

Revision 5644, 3.8 kB (checked in by nakamud, 7 years ago)

lang/ruby/pritter: freezed gems to ease installation

Line 
1module ActiveRecord
2  module Locking
3    # Active Records support optimistic locking if the field <tt>lock_version</tt> is present.  Each update to the
4    # record increments the lock_version column and the locking facilities ensure that records instantiated twice
5    # will let the last one saved raise a StaleObjectError if the first was also updated. Example:
6    #
7    #   p1 = Person.find(1)
8    #   p2 = Person.find(1)
9    #   
10    #   p1.first_name = "Michael"
11    #   p1.save
12    #   
13    #   p2.first_name = "should fail"
14    #   p2.save # Raises a ActiveRecord::StaleObjectError
15    #
16    # You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging,
17    # or otherwise apply the business logic needed to resolve the conflict.
18    #
19    # You must ensure that your database schema defaults the lock_version column to 0.
20    #
21    # This behavior can be turned off by setting <tt>ActiveRecord::Base.lock_optimistically = false</tt>.
22    # To override the name of the lock_version column, invoke the <tt>set_locking_column</tt> method.
23    # This method uses the same syntax as <tt>set_table_name</tt>
24    module Optimistic
25      def self.included(base) #:nodoc:
26        super
27        base.extend ClassMethods
28
29        base.cattr_accessor :lock_optimistically, :instance_writer => false
30        base.lock_optimistically = true
31
32        base.alias_method_chain :update, :lock
33        base.alias_method_chain :attributes_from_column_definition, :lock
34       
35        class << base
36          alias_method :locking_column=, :set_locking_column
37        end
38      end
39
40      def locking_enabled? #:nodoc:
41        lock_optimistically && respond_to?(self.class.locking_column)
42      end
43
44      def attributes_from_column_definition_with_lock
45        result = attributes_from_column_definition_without_lock
46       
47        # If the locking column has no default value set,
48        # start the lock version at zero.  Note we can't use
49        # locking_enabled? at this point as @attributes may
50        # not have been initialized yet
51       
52        if lock_optimistically && result.include?(self.class.locking_column)
53          result[self.class.locking_column] ||= 0
54        end
55       
56        return result
57      end
58
59      def update_with_lock #:nodoc:
60        return update_without_lock unless locking_enabled?
61
62        lock_col = self.class.locking_column
63        previous_value = send(lock_col)
64        send(lock_col + '=', previous_value + 1)
65
66        affected_rows = connection.update(<<-end_sql, "#{self.class.name} Update with optimistic locking")
67          UPDATE #{self.class.table_name}
68          SET #{quoted_comma_pair_list(connection, attributes_with_quotes(false))}
69          WHERE #{self.class.primary_key} = #{quote_value(id)}
70          AND #{self.class.quoted_locking_column} = #{quote_value(previous_value)}
71        end_sql
72
73        unless affected_rows == 1
74          raise ActiveRecord::StaleObjectError, "Attempted to update a stale object"
75        end
76
77        return true
78      end
79
80      module ClassMethods
81        DEFAULT_LOCKING_COLUMN = 'lock_version'
82
83        # Set the column to use for optimistic locking. Defaults to lock_version.
84        def set_locking_column(value = nil, &block)
85          define_attr_method :locking_column, value, &block
86          value
87        end
88
89        # The version column used for optimistic locking. Defaults to lock_version.
90        def locking_column
91          reset_locking_column
92        end
93
94        # Quote the column name used for optimistic locking.
95        def quoted_locking_column
96          connection.quote_column_name(locking_column)
97        end
98
99        # Reset the column used for optimistic locking back to the lock_version default.
100        def reset_locking_column
101          set_locking_column DEFAULT_LOCKING_COLUMN
102        end
103      end
104    end
105  end
106end
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