Class: Alf::Engine::SetAttr

Inherits:
Object
  • Object
show all
Includes:
Cog
Defined in:
lib/alf-engine/alf/engine/set_attr.rb

Overview

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"}
#    ]

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Cog

#each, #to_dot, #to_relation

Constructor Details

#initialize(operand, computation) ⇒ SetAttr

Creates a SetAttr instance



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# File 'lib/alf-engine/alf/engine/set_attr.rb', line 31

def initialize(operand, computation)
  @operand = operand
  @computation = computation
end

Instance Attribute Details

#computation ⇒ TupleComputation (readonly)

Returns Computed attributes as a computation.

Returns:

  • (TupleComputation) —

    Computed attributes as a computation



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# File 'lib/alf-engine/alf/engine/set_attr.rb', line 28

def computation
  @computation
end

#operand ⇒ Enumerable (readonly)

Returns The operand.

Returns:

  • (Enumerable) —

    The operand



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# File 'lib/alf-engine/alf/engine/set_attr.rb', line 25

def operand
  @operand
end

Instance Method Details

#_each ⇒ Object 



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# File 'lib/alf-engine/alf/engine/set_attr.rb', line 37

def _each
  scope = tuple_scope
  operand.each do |tuple|
    computed = @computation.evaluate(scope.__set_tuple(tuple))
    yield tuple.merge(computed)
  end
end