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Fix pessimistic locking examples

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Pratik Naik 2010-08-30 23:52:27 +01:00
parent 9cd708b2cf
commit 0bb32588b7
1 changed files with 4 additions and 4 deletions
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8
railties/guides/source/active_record_querying.textile
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@ -571,13 +571,13 @@ end
h5. Pessimistic Locking
Pessimistic locking uses a locking mechanism provided by the underlying database. Passing +:lock => true+ to +Model.find+ obtains an exclusive lock on the selected rows. +Model.find+ using +:lock+ are usually wrapped inside a transaction for preventing deadlock conditions.
Pessimistic locking uses a locking mechanism provided by the underlying database. Using +lock+ when building a relation obtains an exclusive lock on the selected rows. Relations using +lock+ are usually wrapped inside a transaction for preventing deadlock conditions.
For example:
<ruby>
Item.transaction do
i = Item.first(:lock => true)
i = Item.lock.first
i.name = 'Jones'
i.save
end
@ -592,11 +592,11 @@ Item Update (0.4ms) UPDATE `items` SET `updated_at` = '2009-02-07 18:05:56', `
SQL (0.8ms) COMMIT
</sql>
You can also pass raw SQL to the +:lock+ option to allow different types of locks. For example, MySQL has an expression called +LOCK IN SHARE MODE+ where you can lock a record but still allow other queries to read it. To specify this expression just pass it in as the lock option:
You can also pass raw SQL to the +lock+ method for allowing different types of locks. For example, MySQL has an expression called +LOCK IN SHARE MODE+ where you can lock a record but still allow other queries to read it. To specify this expression just pass it in as the lock option:
<ruby>
Item.transaction do
i = Item.find(1, :lock => "LOCK IN SHARE MODE")
i = Item.lock("LOCK IN SHARE MODE").find(1)
i.increment!(:views)
end
</ruby>