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Contents
module Bmg
module Operator
#
# Allbut operator.
#
# Projects operand's tuples on all but given attributes, that is,
# removes attributes in the list. The operator takes care of removing
# duplicates.
#
# Example:
#
# [{ a: 1, b: 2 }] allbut [:b] => [{ a: 1 }]
#
# All attributes in the butlist SHOULD be existing attributes of the
# input tuples.
#
class Allbut
include Operator::Unary
def initialize(type, operand, butlist)
@type = type
@operand = operand
@butlist = butlist
end
protected
attr_reader :butlist
public
def each
seen = {}
@operand.each do |tuple|
allbuted = tuple_allbut(tuple)
unless seen.has_key?(allbuted)
yield(allbuted)
seen[allbuted] = true
end
end
end
def insert(arg)
case arg
when Hash then operand.insert(valid_tuple!(arg))
when Enumerable then operand.insert(arg.map{|t| valid_tuple!(t) })
else
super
end
end
def update(tuple)
operand.update(valid_tuple!(tuple))
end
def delete
operand.delete
end
def to_ast
[:allbut, operand.to_ast, butlist.dup]
end
protected ### optimization
def _restrict(type, predicate)
operand.restrict(predicate).allbut(butlist)
end
protected ### inspect
def args
[ butlist ]
end
private
def tuple_allbut(tuple)
TupleAlgebra.allbut(tuple, @butlist)
end
def valid_tuple!(tuple)
offending = tuple.keys & butlist
raise InvalidUpdateError, "#{offending.inspect} cannot be updated" unless offending.empty?
tuple
end
end # class Allbut
end # module Operator
end # module Bmg
Version data entries
40 entries across 40 versions & 1 rubygems