Fix RDF.Graph.put/2 to ignore empty RDF.Descriptions

CHANGELOG.md

@@ -23,10 +23,16 @@ This project adheres to [Semantic Versioning](http://semver.org/) and
 
 ### Changed
 
+- `RDF.Description.new` now requires the `subject` to be passed always as first argument;
+  if you want to add some initial data this must be done with the `:init` option
 - for consistency reasons the internal `:id` struct field of `RDF.BlankNode` was renamed
   to `:value` 
-- `RDF.Description.new` now requires the `subject` to be passed always as first argument;
-  if you want to add some initial data this must be done with the `:init` option 
+
+### Fixed
+
+- `RDF.Graph.put/2` ignores empty descriptions; this should be the final piece to ensure
+  that `RDF.Graph`s never contain empty descriptions, which would distort results of 
+  functions like `RDF.Graph.subjects/1`, `RDF.Graph.subject_count/1`, `RDF.Graph.descriptions/1`   
 
 
 [Compare v0.8.2...HEAD](https://github.com/rdf-elixir/rdf-ex/compare/v0.8.2...HEAD)

lib/rdf/graph.ex

@@ -250,8 +250,13 @@ defmodule RDF.Graph do
   def put(graph, {subject, predicate, object, _}),
     do: put(graph, {subject, predicate, object})
 
-  def put(%__MODULE__{} = graph, %Description{subject: subject} = description),
-    do: do_put(graph, subject, description)
+  def put(%__MODULE__{} = graph, %Description{subject: subject} = description) do
+    if Description.count(description) > 0 do
+      do_put(graph, subject, description)
+    else
+      graph
+    end
+  end
 
   def put(graph, %__MODULE__{descriptions: descriptions, prefixes: prefixes}) do
     graph =

test/unit/graph_test.exs

@@ -244,6 +244,11 @@ defmodule RDF.GraphTest do
       assert graph_includes_statement?(g, {EX.Subject1, EX.predicate3(), EX.Object3})
     end
 
+    test "an empty description is ignored" do
+      g = Graph.new() |> Graph.add(Description.new(EX.Subject))
+      assert empty_graph?(g)
+    end
+
     test "a list of descriptions" do
       g =
         Graph.add(graph(), [
@@ -402,6 +407,11 @@ defmodule RDF.GraphTest do
       assert graph_includes_statement?(g, {EX.S2, EX.P2, EX.O2})
     end
 
+    test "an empty description is ignored" do
+      g = Graph.new() |> Graph.put(Description.new(EX.Subject))
+      assert empty_graph?(g)
+    end
+
     test "a list of descriptions" do
       g =
         Graph.new([{EX.S1, EX.p1(), EX.O1}, {EX.S2, EX.p2(), EX.O2}, {EX.S1, EX.p3(), EX.O3}])