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module Arel
module Predicates
class Predicate
def or(other_predicate)
Or.new(self, other_predicate)
end
def and(other_predicate)
And.new(self, other_predicate)
end
def not
Not.new(self)
end
end
class Polyadic < Predicate
attributes :operator, :operand1, :additional_operands
def initialize(operator, operand1, *additional_operands)
@operator = operator
@operand1 = operand1
@additional_operands = additional_operands.uniq
end
def ==(other)
self.class === other and
@operator == operator and
@operand1 == other.operand1 and
same_elements?(@additional_operands, other.additional_operands)
end
def bind(relation)
self.class.new(
operator,
operand1.find_correlate_in(relation),
*additional_operands.map {|o| o.find_correlate_in(relation)}
)
end
private
def same_elements?(a1, a2)
[:select, :inject, :size].each do |m|
return false unless [a1, a2].each {|a| a.respond_to?(m) }
end
a1.inject({}) { |h,e| h[e] = a1.select { |i| i == e }.size; h } ==
a2.inject({}) { |h,e| h[e] = a2.select { |i| i == e }.size; h }
end
end
class Unary < Predicate
attributes :operand
deriving :initialize, :==
def bind(relation)
self.class.new(operand.find_correlate_in(relation))
end
end
class Binary < Predicate
attributes :operand1, :operand2
deriving :initialize
def ==(other)
self.class === other and
@operand1 == other.operand1 and
@operand2 == other.operand2
end
def bind(relation)
self.class.new(operand1.find_correlate_in(relation), operand2.find_correlate_in(relation))
end
end
class Equality < Binary
def ==(other)
Equality === other and
((operand1 == other.operand1 and operand2 == other.operand2) or
(operand1 == other.operand2 and operand2 == other.operand1))
end
end
class Inequality < Equality; end
class GreaterThanOrEqualTo < Binary; end
class GreaterThan < Binary; end
class LessThanOrEqualTo < Binary; end
class LessThan < Binary; end
class Match < Binary; end
class NotMatch < Binary; end
class In < Binary; end
class NotIn < Binary; end
end
end
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