Add Solutions#merge based on JOIN semantics.

Author: gkellogg

lib/rdf/query/solutions.rb

@@ -112,6 +112,21 @@ def dup
       RDF::Query::Solutions.new(self.compact.map(&:dup))
     end
 
+    ##
+    # Merge solutions in `other` into a new solutions instance. Each solution in `other` is merged into those solutions in `self` that are compatible.
+    #
+    # @param [RDF::Query::Solutions] other
+    # @return [RDF::Query::Solutions]
+    def merge(other)
+      other ||= RDF::Query::Solutions()
+      return other if self.empty?
+      return self if other.empty?
+
+      RDF::Query::Solutions(self.map do |s1|
+        other.map { |s2| s2.merge(s1) if s2.compatible?(s1) }
+      end.flatten.compact)
+    end
+
     ##
     # Filters this solution sequence by the given `criteria`.
     #

spec/query_solutions_spec.rb

@@ -67,6 +67,64 @@
     end
   end
 
+  describe "merge" do
+    {
+      "add x dijoint" => [
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/b")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/c")),
+        ]),
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(x: RDF::URI("http://example.org/x")),
+        ]),
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), x: RDF::URI("http://example.org/x")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/b"), x: RDF::URI("http://example.org/x")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/c"), x: RDF::URI("http://example.org/x")),
+        ]),
+      ],
+      "add x shared" => [
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), x: RDF::URI("http://example.org/x")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/b"), x: RDF::URI("http://example.org/x")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/c"), x: RDF::URI("http://example.org/x")),
+        ]),
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), y: RDF::URI("http://example.org/y")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/b"), y: RDF::URI("http://example.org/y")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/c"), y: RDF::URI("http://example.org/y")),
+        ]),
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), x: RDF::URI("http://example.org/x"), y: RDF::URI("http://example.org/y")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/b"), x: RDF::URI("http://example.org/x"), y: RDF::URI("http://example.org/y")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/c"), x: RDF::URI("http://example.org/x"), y: RDF::URI("http://example.org/y")),
+        ]),
+      ],
+      "add x disjoint" => [
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), x: RDF::URI("http://example.org/x")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/b"), x: RDF::URI("http://example.org/x")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/c"), x: RDF::URI("http://example.org/x")),
+        ]),
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), y: RDF::URI("http://example.org/y")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/d"), y: RDF::URI("http://example.org/y")),
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/e"), y: RDF::URI("http://example.org/y")),
+        ]),
+        RDF::Query::Solutions.new.concat([
+          RDF::Query::Solution.new(animal: RDF::URI("http://example.org/a"), x: RDF::URI("http://example.org/x"), y: RDF::URI("http://example.org/y")),
+        ]),
+      ],
+    }.each do |name, (left, right, result)|
+      it name do
+        expect(left.merge(right)).to be_a(Enumerable)
+        expect(left.merge(right)).to be_a(RDF::Query::Solutions)
+        expect(left.merge(right).to_a).to eq result.to_a
+      end
+    end
+  end
+
   describe "#-" do
     {
       "subsetByExcl01" => [