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Contents
# Will fetch the next N values from a sequence and store it in a queue.
# Now the values will can be fetched from the queue without any database roundtrip.
# If the queue is empty, the next N values will be fetched from database and stored in the queue.
#
# It's using the DUAL table so it should only work with oracle.
#
# Author:: Andre Kullmann
#
module ActiveRecord
module Bulkoperation
module Util
class SequenceCache
#
# seq - the sequence name to use with the SequenceCache object
# refetch - how many values should be fetch from the database with each roundtrip
def initialize(seq, prefetch = 10)
@seq, @prefetch = seq, prefetch
@queue = Queue.new
end
#
# return - the next value from the sequence
def next_value
while ( value = next_value_from_queue ).nil?
fill_queue
end
value
end
private
def next_value_from_queue
@queue.pop(true)
rescue ThreadError => e
nil
end
def fill_queue
fetch.each do |f|
@queue << f
end
end
def fetch
st = ActiveRecord::Base.connection.exec_query("SELECT #{@seq}.nextval id FROM dual connect by level <= :a", "SQL", [[nil,@prefetch]])
st.map {|r| r['id']}
end
end
end
end
end
Version data entries
7 entries across 7 versions & 1 rubygems