Class: RDF::Query::Solutions

Inherits:
Array
  • Object
show all
Defined in:
lib/rdf/query/solutions.rb

Overview

An RDF basic graph pattern (BGP) query solution sequence.

Examples:

Filtering solutions using a hash

solutions.filter(:author  => RDF::URI("http://ar.to/#self"))
solutions.filter(:author  => "Arto Bendiken")
solutions.filter(:author  => [RDF::URI("http://ar.to/#self"), "Arto Bendiken"])
solutions.filter(:updated => RDF::Literal(Date.today))

Filtering solutions using a block

solutions.filter { |solution| solution.author.literal? }
solutions.filter { |solution| solution.title =~ /^SPARQL/ }
solutions.filter { |solution| solution.price < 30.5 }
solutions.filter { |solution| solution.bound?(:date) }
solutions.filter { |solution| solution.age.datatype == RDF::XSD.integer }
solutions.filter { |solution| solution.name.language == :es }

Reordering solutions based on a variable or proc

solutions.order_by(:updated)
solutions.order_by(:updated, :created)
solutions.order_by(:updated, lambda {|a, b| b <=> a})

Selecting/Projecting particular variables only

solutions.select(:title)
solutions.select(:title, :description)
solutions.project(:title)

Eliminating duplicate solutions

solutions.distinct

Limiting the number of solutions

solutions.offset(20).limit(10)

Counting the number of matching solutions

solutions.count
solutions.count { |solution| solution.price < 30.5 }

Iterating over all found solutions

solutions.each { |solution| puts solution.inspect }

Since:

  • 0.3.0

Instance Method Summary collapse

Instance Method Details

#bindings ⇒ Hash{Symbol => Array<RDF::Term>}

Returns hash of bindings from each solution. Each bound variable will have an array of bound values representing those from each solution, where a given solution will have just a single value for each bound variable

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 68

def bindings
  bindings = {}
  each do |solution|
    solution.each do |key, value|
      bindings[key] ||= []
      bindings[key] << value
    end
  end
  bindings
end

#count ⇒ Integer #count({ |solution| ... }) {|solution| ... } ⇒ Integer

Returns the number of matching query solutions.

Overloads:

  • #count ⇒ Integer

    Returns:

    • (Integer)
  • #count({ |solution| ... }) {|solution| ... } ⇒ Integer

    Yields:

    • (solution)

    Yield Parameters:

    Yield Returns:

    • (Boolean)

    Returns:

    • (Integer)

Returns:

  • (Integer)

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 59

def count(&block)
  super
end

#distinct ⇒ void Also known as: distinct!, reduced, reduced!

This method returns an undefined value.

Ensures that the solutions in this solution sequence are unique.

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 165

def distinct
  self.uniq!
  self
end

#filter(criteria = {}) {|solution| ... } ⇒ void Also known as: filter!

This method returns an undefined value.

Filters this solution sequence by the given ‘criteria`.

Parameters:

  • criteria (Hash{Symbol => Object}) (defaults to: {})

Yields:

  • (solution)

Yield Parameters:

Yield Returns:

  • (Boolean)

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 87

def filter(criteria = {}, &block)
  if block_given?
    self.reject! do |solution|
      !block.call(solution.is_a?(Solution) ? solution : Solution.new(solution))
    end
  else
    self.reject! do |solution|
      solution = solution.is_a?(Solution) ? solution : Solution.new(solution)
      results = criteria.map do |name, value|
        solution[name] == value
      end
      !results.all?
    end
  end
  self
end

#have_variables?(variables) ⇒ Boolean Also known as: has_variables?

Returns ‘true` if this solution sequence contains bindings for any of the given `variables`.

Parameters:

  • variables (Array<Symbol, #to_sym>) —

    an array of variables to check

Returns:

  • (Boolean) —

    ‘true` or `false`

See Also:

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 232

def have_variables?(variables)
  self.any? { |solution| solution.has_variables?(variables) }
end

#limit(length) ⇒ void Also known as: limit!

This method returns an undefined value.

Limits the number of solutions in this solution sequence to a maximum of ‘length`.

Parameters:

  • length (Integer, #to_i) —

    zero or a positive integer

Raises:

  • (ArgumentError) —

    if ‘length` is negative

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 197

def limit(length)
  length = length.to_i
  raise ArgumentError, "expected zero or a positive integer, got #{length}" if length < 0
  case length
    when 0 then self.clear
    else self.slice!(length..-1) if length < self.size
  end
  self
end

#offset(start) ⇒ void Also known as: offset!

This method returns an undefined value.

Limits this solution sequence to bindings starting from the ‘start` offset in the overall solution sequence.

Parameters:

  • start (Integer, #to_i) —

    zero or a positive or negative integer

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 180

def offset(start)
  case start = start.to_i
    when 0 then nil
    else self.slice!(0...start)
  end
  self
end

#order(*variables) {|solution| ... } ⇒ void Also known as: order_by

This method returns an undefined value.

Reorders this solution sequence by the given ‘variables`.

Variables may be symbols or Variable instances. A variable may also be a Procedure/Lambda, compatible with Enumerable#sort. This takes two arguments (solutions) and returns -1, 0, or 1 equivalently to <=>.

If called with a block, variables are ignored, and the block is invoked with pairs of solutions. The block is expected to return -1, 0, or 1 equivalently to <=>.

Parameters:

Yields:

  • (solution)

Yield Parameters:

Yield Returns:

  • (Integer) —

    -1, 0, or 1 depending on value of comparator

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 121

def order(*variables, &block)
  if variables.empty? && !block_given?
    raise ArgumentError, "wrong number of arguments (0 for 1)"
  else
    self.sort! do |a, b|
      if block_given?
        block.call((a.is_a?(Solution) ? a : Solution.new(a)), (b.is_a?(Solution) ? b : Solution.new(b)))
      else
        # Try each variable until a difference is found.
        variables.inject(nil) do |memo, v|
          memo || begin
            comp = v.is_a?(Proc) ? v.call(a, b) : (v = v.to_sym; a[v] <=> b[v])
            comp == 0 ? false : comp
          end
        end || 0
      end
    end
  end
  self
end

#project(*variables) ⇒ void Also known as: select

This method returns an undefined value.

Restricts this solution sequence to the given ‘variables` only.

Parameters:

  • variables (Array<Symbol, #to_sym>)

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 148

def project(*variables)
  if variables.empty?
    raise ArgumentError, "wrong number of arguments (0 for 1)"
  else
    variables.map!(&:to_sym)
    self.each do |solution|
      solution.bindings.delete_if { |k, v| !variables.include?(k.to_sym) }
    end
  end
  self
end

#variable_names ⇒ Array<Symbol>

Returns an array of the distinct variable names used in this solution sequence.

Returns:

  • (Array<Symbol>)

Since:

  • 0.3.0



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# File 'lib/rdf/query/solutions.rb', line 213

def variable_names
  variables = self.inject({}) do |result, solution|
    solution.each_name do |name|
      result[name] ||= true
    end
    result
  end
  variables.keys
end