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Contents
module Alf
module Engine
#
# Set computed tuples attributes. This cog allows implementing both
# EXTEND and UPDATE relational operators.
#
# Example:
#
# rel = [
# {:name => "Jones", :city => "London"}
# ]
# comp = TupleComputation[
# :city => lambda{ city.upcase },
# :concat => lambda{ "#{name} #{city}" }
# ]
# SetAttr.new(rel, comp).to_a
# # => [
# # {:name => "Jones", :city => "LONDON", :concat => "Jones LONDON"}
# # ]
#
class SetAttr < Cog
# @return [Enumerable] The operand
attr_reader :operand
# @return [TupleComputation] Computed attributes as a computation
attr_reader :computation
# Creates a SetAttr instance
def initialize(operand, computation)
@operand = operand
@computation = computation
end
# (see Cog#each)
def each
handle = Tools::TupleHandle.new
operand.each do |tuple|
computed = @computation.evaluate(handle.set(tuple))
yield tuple.merge(computed){|k,v1,v2| v2}
end
end
end # class SetAttr
end # module Engine
end # module Alf
Version data entries
5 entries across 5 versions & 1 rubygems