class LD::Patch::Algebra::Cut

The LD Patch ‘cut` operator.

The Cut operation is recursively remove triples from some starting node.

@example

(cut ?a)

Constants

NAME

Public Instance Methods

execute(queryable, options = {}) click to toggle source

Executes this upate on the given ‘writable` graph or repository.

@param [RDF::Queryable] queryable

the graph or repository to write

@param [Hash{Symbol => Object}] options

any additional options

@return [RDF::Query::Solutions] A single solution including passed bindings with ‘var` bound to the solution. @raise [IOError]

If no triples are identified, or the operand is an unbound variable or the operand is an unbound variable.

@see www.w3.org/TR/sparql11-update/

# File lib/ld/patch/algebra/cut.rb, line 28
def execute(queryable, options = {})
  debug(options) {"Cut"}
  bindings = options.fetch(:bindings)
  solution = bindings.first
  var = operand(0)

  # Bind variable
  raise LD::Patch::Error.new("Operand uses unbound variable #{var.inspect}", code: 400) unless solution.bound?(var)
  var = solution[var]

  cut_count = 0
  # Get triples to delete using consice bounded description
  queryable.concise_bounded_description(var) do |statement|
    queryable.delete(statement)
    cut_count += 1
  end

  # Also delete triples having var in the object position
  queryable.query({object: var}).each do |statement|
    queryable.delete(statement)
    cut_count += 1
  end

  raise LD::Patch::Error, "Cut removed no triples" unless cut_count > 0

  bindings
end