Class: RDF::Query

Inherits:
Object
  • Object
show all
Defined in:
lib/rdf/query.rb,
lib/rdf/query/result.rb,
lib/rdf/query/binding.rb,
lib/rdf/query/executer.rb

Overview

An RDF graph query. This represents a complex query that joins several triples. To query for a simple triple, see the match method on RDF::Graph::Memory.

A Query is created then passed to the execute method on a graph. In some graph implementations the execute method may delegate to the underlying triple store, but in other cases the execute method may be mixed in from RDF::Query::Executer.

At some point I’d like to steal the query DSL from Semitar.

Example:

q = RDF::Query.new.select(:a, :c).
                   where(:a, RDF::type, :b).
                   and(:b, RDFS::subClassOf, RDF::Property).
                   and(:b, RDFS::comment, :c)
result = some_graph.execute(q)

Defined Under Namespace

Modules: Executer Classes: Binding, Result

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Query

Creates a new Query.



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# File 'lib/rdf/query.rb', line 23

def initialize
  @select_clause = []
  @where_clause = []
end

Instance Method Details

#select(*a) ⇒ Object

Adds items to the select clause of this query. When this query is executed, the results will include bindings for these variables.



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# File 'lib/rdf/query.rb', line 30

def select(*a)
  @select_clause = a
  self
end

#select_clause ⇒ Object

Returns the select clause for this query.



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# File 'lib/rdf/query.rb', line 36

def select_clause
  @select_clause.clone
end

#where(s, p, o) ⇒ Object Also known as: and

Adds the triple s p o to the where clause of this query. When the query is executed, the where clause will constrain the results.



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# File 'lib/rdf/query.rb', line 42

def where(s, p, o)
  @where_clause << [s, p, o]
  self
end

#where_clause ⇒ Object

Returns the where clause for this query.



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# File 'lib/rdf/query.rb', line 48

def where_clause
  @where_clause.clone
end