Class: SPARQL::Algebra::Operator::Concat

Inherits:
Operator
  • Object
show all
Includes:
Evaluatable
Defined in:
lib/sparql/algebra/operator/concat.rb

Overview

A SPARQL concat operator.

The CONCAT function corresponds to the XPath fn:concat function. The function accepts string literals as arguments.

[121] BuiltInCall ::= ... 'CONCAT' ExpressionList

Examples:

SPARQL Grammar

PREFIX : <http://example.org/>
SELECT (CONCAT(?str1,?str2) AS ?str) WHERE {
  :s6 :str ?str1 .
  :s7 :str ?str2 .
}

SSE

(prefix
 ((: <http://example.org/>))
 (project (?str)
  (extend ((?str (concat ?str1 ?str2)))
   (bgp
    (triple :s6 :str ?str1)
    (triple :s7 :str ?str2)))))

See Also:

Constant Summary collapse

NAME = 
:concat

Instance Method Summary collapse

Methods included from Evaluatable

#apply, #memoize, #replace_aggregate!, #replace_vars!

Instance Method Details

#evaluate(bindings, **options) ⇒ RDF::Term

The lexical form of the returned literal is obtained by concatenating the lexical forms of its inputs. If all input literals are typed literals of type xsd:string, then the returned literal is also of type xsd:string, if all input literals are plain literals with identical language tag, then the returned literal is a plain literal with the same language tag, in all other cases, the returned literal is a simple literal.

Examples:

concat("foo", "bar")                         #=> "foobar"
concat("foo"@en, "bar"@en)                   #=> "foobar"@en
concat("foo"^^xsd:string, "bar"^^xsd:string) #=> "foobar"^^xsd:string
concat("foo", "bar"^^xsd:string)             #=> "foobar"
concat("foo"@en, "bar")                      #=> "foobar"
concat("foo"@en, "bar"^^xsd:string)          #=> "foobar"

Parameters:

  • bindings (RDF::Query::Solution) —

    a query solution containing zero or more variable bindings

  • options (Hash{Symbol => Object}) —

    ({}) options passed from query

Returns:

Raises:

  • (TypeError) —

    if any operand is not a literal



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# File 'lib/sparql/algebra/operator/concat.rb', line 50

def evaluate(bindings, **options)
  ops = operands.map {|op| op.evaluate(bindings, **options.merge(depth: options[:depth].to_i + 1))}

  # rdf:nil is like empty string
  if ops == [RDF.nil]
    return RDF::Literal.new("")
  end

  raise TypeError, "expected all plain literal operands" unless ops.all? {|op| op.literal? && op.plain?}

  ops.inject do |memo, op|
    case
    when memo.datatype == RDF::XSD.string && op.datatype == RDF::XSD.string
      RDF::Literal.new("#{memo}#{op}", datatype: RDF::XSD.string)
    when memo.has_language? && memo.language == op.language
      RDF::Literal.new("#{memo}#{op}", language: memo.language)
    else
      RDF::Literal.new("#{memo}#{op}")
    end
  end
end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

  • (String) 


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# File 'lib/sparql/algebra/operator/concat.rb', line 77

def to_sparql(**options)
  "CONCAT(#{operands.to_sparql(delimiter: ', ', **options)})"
end