57 lines
2.0 KiB
Ruby
57 lines
2.0 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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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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if locking_enabled?
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previous_value = self.lock_version
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self.lock_version = previous_value + 1
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affected_rows = connection.update(
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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)} AND lock_version = #{quote(previous_value)}",
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"#{self.class.name} Update with optimistic locking"
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)
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raise(ActiveRecord::StaleObjectError, "Attempted to update a stale object") unless affected_rows == 1
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else
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update_without_lock
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end
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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?(:lock_version)
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end
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end
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end |