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Contents
module Bmg
module Operator
#
# Matching operator.
#
# Filters tuples of left operand to those matching at least
# one tuple in right operand.
#
class Matching
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
return to_enum unless block_given?
index = Hash.new
right.each_with_object(index) do |t, index|
key = tuple_project(t, on)
index[key] = true
end
left.each do |tuple|
key = tuple_project(tuple, on)
yield tuple if index.has_key?(key)
end
end
def to_ast
[ :matching, left.to_ast, right.to_ast, on ]
end
protected ### optimization
def _restrict(type, predicate)
# Predicate can always be fully applied to left
new_left = left.restrict(predicate)
# regarding right... the predicate possibly makes references
# to the join key, but also to left attributes... let split
# on the join key attributes, to try to remove spurious
# attributes for right...
on_on_and_more, left_only = predicate.and_split(on)
# it's not guaranteed! let now check whether the split led
# to a situation where the predicate on `on` attributes
# actually refers to no other ones...
if !on_on_and_more.tautology? and (on_on_and_more.free_variables - on).empty?
new_right = right.restrict(on_on_and_more)
else
new_right = right
end
new_left.matching(new_right, on)
rescue Predicate::NotSupportedError
super
end
protected ### inspect
def args
[ on ]
end
private
def tuple_project(tuple, on)
TupleAlgebra.project(tuple, on)
end
end # class Matching
end # module Operator
end # module Bmg
Version data entries
31 entries across 31 versions & 1 rubygems