80 lines
2.6 KiB
Ruby
80 lines
2.6 KiB
Ruby
module ActiveRecord
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# Active Records support optimistic locking if the field <tt>lock_version</tt> is present. Each update to the
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# record increments the lock_version column and the locking facilities ensure that records instantiated twice
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# will let the last one saved raise a StaleObjectError if the first was also updated. Example:
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#
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# p1 = Person.find(1)
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# p2 = Person.find(1)
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#
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# p1.first_name = "Michael"
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# p1.save
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#
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# p2.first_name = "should fail"
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# p2.save # Raises a ActiveRecord::StaleObjectError
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#
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# You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging,
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# or otherwise apply the business logic needed to resolve the conflict.
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#
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# You must ensure that your database schema defaults the lock_version column to 0.
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#
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# This behavior can be turned off by setting <tt>ActiveRecord::Base.lock_optimistically = false</tt>.
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# To override the name of the lock_version column, invoke the <tt>set_locking_column</tt> method.
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# This method uses the same syntax as <tt>set_table_name</tt>
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module Locking
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def self.append_features(base) #:nodoc:
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super
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base.class_eval do
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alias_method :update_without_lock, :update
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alias_method :update, :update_with_lock
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end
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end
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def update_with_lock #:nodoc:
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return update_without_lock unless locking_enabled?
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lock_col = self.class.locking_column
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previous_value = send(lock_col)
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send(lock_col + '=', previous_value + 1)
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affected_rows = connection.update(<<-end_sql, "#{self.class.name} Update with optimistic locking")
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UPDATE #{self.class.table_name}
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SET #{quoted_comma_pair_list(connection, attributes_with_quotes(false))}
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WHERE #{self.class.primary_key} = #{quote(id)}
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AND #{lock_col} = #{quote(previous_value)}
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end_sql
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unless affected_rows == 1
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raise ActiveRecord::StaleObjectError, "Attempted to update a stale object"
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end
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return true
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end
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end
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class Base
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@@lock_optimistically = true
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cattr_accessor :lock_optimistically
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def locking_enabled? #:nodoc:
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lock_optimistically && respond_to?(self.class.locking_column)
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end
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class << self
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def set_locking_column(value = nil, &block)
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define_attr_method :locking_column, value, &block
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end
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def locking_column #:nodoc:
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reset_locking_column
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end
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def reset_locking_column #:nodoc:
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default = 'lock_version'
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set_locking_column(default)
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default
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end
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end
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end
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end
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