Better support for non-distinguished variables.

Author: gkellogg

lib/rdf/query.rb

@@ -359,8 +359,9 @@ def execute(queryable, solutions: Solution.new, graph_name: nil, name: nil, **op
         return @solutions if @solutions.empty?
 
         if !pattern.optional?
-          # We have no solutions for variables we should have solutions for:
-          need_vars = pattern.variables.keys
+          # We have no solutions for variables we should have solutions for
+          # (excludes non-distinguished variables):
+          need_vars = pattern.variables.select {|k,v| v.distinguished?}.keys
           @solutions.each do |solution|
             break if need_vars.empty?
             need_vars -= solution.bindings.keys

lib/rdf/query/variable.rb

@@ -65,9 +65,12 @@ class Variable
     #   the variable name
     # @param  [RDF::Term] value
     #   an optional variable value
-    def initialize(name = nil, value = nil)
+    # @param [Boolean] distinguished (true)
+    #   defaults to false, unless name looks like a bnode
+    def initialize(name = nil, value = nil, distinguished: true)
       @name  = (name || "g#{__id__.to_i.abs}").to_sym
       @value = value
+      @distinguished = distinguished
     end
 
     ##
@@ -109,7 +112,7 @@ def unbound?
     #
     # @return [Boolean]
     def distinguished?
-      @distinguished.nil? || @distinguished
+      @distinguished
     end
 
     ##

spec/query_spec.rb

@@ -602,7 +602,27 @@
         its(:variables) {is_expected.to include(:g)}
       end
     end
-    
+
+    context "with non-distinguished variables" do
+      before :each do
+        @graph = RDF::Graph.new do |graph|
+          graph << [EX.s1, EX.p, EX.o]
+          graph << [EX.s2, EX.p, EX.o]
+          graph << [EX.s2, EX.p2, EX.o2]
+        end
+      end
+
+      it "matches graphs with a bound non-distinguished variable" do
+        query = RDF::Query.new do |query|
+          query.pattern [:s, EX.p, EX.o]
+          query.pattern [RDF::Query::Variable.new(:s2, distinguished: false), EX.p2, EX.o2]
+        end
+        expect(query.execute(@graph)).to have_result_set([{ s: EX.s1, s2: EX.s2 }, { s: EX.s2, s2: EX.s2 }])
+      end
+
+      it "matches graphs with a unbound non-distinguished variable"
+    end
+
     context "with an optional pattern" do
       before :each do
         @graph = RDF::Graph.new do |graph|

spec/query_variable_spec.rb

@@ -1,12 +1,12 @@
 require File.join(File.dirname(__FILE__), 'spec_helper')
 
 describe RDF::Query::Variable do
-  context ".new(:x)" do
+  context ".new unbound" do
     let(:var) {RDF::Query::Variable.new(:x)}
     subject {var}
 
     it "is named" do
-      expect(subject.named?).to be_truthy
+      expect(subject).to be_named
       expect(subject.name).to eq :x
     end
 
@@ -35,6 +35,10 @@
         expect(subject).to_not be_distinguished
       end
 
+      it "can be created as non-distinguished" do
+        expect(described_class.new(:x, distinguished: false)).not_to be_distinguished
+      end
+
       it "can be made distinguished" do
         subject.distinguished = true
         expect(subject).to be_distinguished
@@ -49,7 +53,6 @@
       expect(subject.to_sym).to eq :x
     end
 
-
     it "has no value" do
       expect(subject.value).to be_nil
     end
@@ -104,7 +107,33 @@
     end
   end
 
-  context ".new(:x, 123)" do
+  context ".new non-distinguished" do
+    subject {RDF::Query::Variable.new(:x, RDF::Literal(123))}
+
+    it "has a value" do
+      expect(subject.value).to eq RDF::Literal(123)
+    end
+
+    it "is bound" do
+      expect(subject).not_to be_unbound
+      expect(subject).to be_bound
+      expect(subject.variables).to eq({x: subject})
+      expect(subject.bindings).to eq({x: RDF::Literal(123)})
+    end
+
+    it "matches only its value" do
+      [nil, true, false, RDF::Literal(456)].each do |value|
+        expect((subject === value)).to be_falsey
+      end
+      expect((subject === RDF::Literal(123))).to be_truthy
+    end
+
+    it "has a string representation" do
+      expect(subject.to_s).to eq "?x=123"
+    end
+  end
+
+  context ".new bound" do
     subject {RDF::Query::Variable.new(:x, RDF::Literal(123))}
 
     it "has a value" do