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Locks

Model lock
You can use lock using with_lock method on query collection:
Clear::SQL.transaction do
    # SELECT * FROM users WHERE organization = 'Crystal Lang' FOR UPDATE
    User.where(organization: "Crystal Lang").with_lock.each do |user|
        # Do something with your users
    end
end
with_lock offers optional parameters (default: "FOR UPDATE"), to setup the lock options you want (ex: with_lock("FOR UPDATE SKIP LOCKED"))
See PostgreSQL deep explanation about locking here.
Lock work only inside transaction. Without transaction block, the call might fail.
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Connection pool

Next - Querying

The collection object

Last modified 3yr ago