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Contents
module Bmg
module Operator
#
# Join operator.
#
# Natural join, following relational algebra
#
class Join
include Operator::Binary
def initialize(type, left, right, on)
@type = type
@left = left
@right = right
@on = on
end
private
attr_reader :on
public
def each
index = Hash.new
right.each_with_object(index) do |t, index|
key = tuple_project(t, on)
index[key] ||= []
index[key] << t
end
left.each do |tuple|
key = tuple_project(tuple, on)
if to_join = index[key]
to_join.each do |right|
yield right.merge(tuple)
end
end
end
end
def to_ast
[ :join, left.to_ast, right.to_ast, on ]
end
protected ### optimization
def _autowrap(type, options)
u_left, left_replaced = _unautowrap(left, options)
u_right, right_replaced = _unautowrap(right, options)
if (!left_replaced && !right_replaced)
super
else
u_left.join(u_right, on).autowrap(options)
end
end
def _unautowrap(operand, options)
return [operand, false] unless operand.is_a?(Operator::Autowrap)
return [operand, false] unless operand.same_options?(options)
[operand.send(:operand), true]
end
private :_unautowrap
protected ### inspect
def args
[ on ]
end
private
def tuple_project(tuple, on)
TupleAlgebra.project(tuple, on)
end
end # class Join
end # module Operator
end # module Bmg
Version data entries
12 entries across 12 versions & 1 rubygems