feature/add handle quads

README.md

@@ -199,6 +199,12 @@ To write N-Triples (or N-Quads) instead, pass a `format` argument upon creation
 const writer1 = new N3.Writer({ format: 'N-Triples' });
 const writer2 = new N3.Writer({ format: 'application/trig' });
 ```
+To exclude the graph name from the serialization, pass a `graphs` argument upon creation:
+```JavaScript
+const writer3 = new N3.Writer({ graphs: 'keep' });  // Keeps the graph names (default)
+const writer4 = new N3.Writer({ graphs: 'drop' });  // Drops the graph name
+const writer5 = new N3.Writer({ graphs: 'error' }); // Throws an error when writing a graph name
+```
 
 ### From quads to an RDF stream
 

src/N3Writer.js

@@ -35,6 +35,9 @@ export default class N3Writer {
       options = outputStream, outputStream = null;
     options = options || {};
     this._lists = options.lists;
+    this._keepGraphs = !options.graphs || options.graphs === 'keep';
+    this._errorOnGraphs = options.graphs === 'error';
+
 
     // If no output stream given, send the output as string through the end callback
     if (!outputStream) {
@@ -84,8 +87,11 @@ export default class N3Writer {
   // ### `_writeQuad` writes the quad to the output stream
   _writeQuad(subject, predicate, object, graph, done) {
     try {
+      if (this._errorOnGraphs && !DEFAULTGRAPH.equals(graph)) {
+        done(new Error('The chosen serialization settings do not support triples in a non-default graph.'));
+      }
       // Write the graph's label if it has changed
-      if (!graph.equals(this._graph)) {
+      if (this._keepGraphs && !graph.equals(this._graph)) {
         // Close the previous graph and start the new one
         this._write((this._subject === null ? '' : (this._inDefaultGraph ? '.\n' : '\n}\n')) +
                     (DEFAULTGRAPH.equals(graph) ? '' : `${this._encodeIriOrBlank(graph)} {\n`));
@@ -117,15 +123,20 @@ export default class N3Writer {
   _writeQuadLine(subject, predicate, object, graph, done) {
     // Write the quad without prefixes
     delete this._prefixMatch;
-    this._write(this.quadToString(subject, predicate, object, graph), done);
+    this._write(this.quadToString(subject, predicate, object, graph, done), done);
   }
 
   // ### `quadToString` serializes a quad as a string
-  quadToString(subject, predicate, object, graph) {
+  quadToString(subject, predicate, object, graph, done) {
+    if (this._errorOnGraphs && !DEFAULTGRAPH.equals(graph)) {
+      const error = new Error('The chosen serialization settings do not support triples in a non-default graph.');
+      if (done) return done(error);
+      throw error;
+    }
     return  `${this._encodeSubject(subject)} ${
             this._encodeIriOrBlank(predicate)} ${
             this._encodeObject(object)
-            }${graph && graph.value ? ` ${this._encodeIriOrBlank(graph)} .\n` : ' .\n'}`;
+          }${this._keepGraphs && graph && graph.value ? ` ${this._encodeIriOrBlank(graph)} .\n` : ' .\n'}`;
   }
 
   // ### `quadsToString` serializes an array of quads as a string

test/N3Writer-test.js

@@ -31,6 +31,17 @@ describe('Writer', () => {
       const writer = new Writer();
       writer.quadToString(new NamedNode('a'), new NamedNode('b'), new NamedNode('c'), new NamedNode('g')).should.equal('<a> <b> <c> <g> .\n');
     });
+    it('should throw error when it\'s forbidden to pass graphname', done => {
+      const writer = new Writer({ graphs: 'error' });
+      try {
+        writer.quadToString(new NamedNode('a'), new NamedNode('b'), new NamedNode('c'), new NamedNode('g')).should.equal('<a> <b> <c> <g> .\n');
+      }
+      catch (error) {
+        error.should.be.an.instanceof(Error);
+        error.should.have.property('message', 'The chosen serialization settings do not support triples in a non-default graph.');
+        done();
+      }
+    });
 
     it('should serialize an array of triples', () => {
       const writer = new Writer();
@@ -656,6 +667,57 @@ describe('Writer', () => {
       });
     });
 
+    it('ignores the graph name when needed in N-Quads mode', done => {
+      const writer = new Writer({ graphs: 'ignore', format: 'n-quads' });
+      writer.addQuad(new Quad(
+        new NamedNode('a:a'),
+        new NamedNode('b:b'),
+        new NamedNode('c:c'),
+        new NamedNode('g:g')));
+      writer.end((error, output) => {
+        output.should.equal('<a:a> <b:b> <c:c> .\n');
+        done(error);
+      });
+    });
+
+    it('throws an graph-found error needed in N-Quads mode', done => {
+      const writer = new Writer({ graphs: 'error', format: 'n-quads' });
+      writer.addQuad(new Quad(
+        new NamedNode('a:a'),
+        new NamedNode('b:b'),
+        new NamedNode('c:c'),
+        new NamedNode('g:g')), error => {
+        error.should.be.an.instanceof(Error);
+        error.should.have.property('message', 'The chosen serialization settings do not support triples in a non-default graph.');
+        done();
+      });
+    });
+    it('ignores the graph name when needed', done => {
+      const writer = new Writer({ graphs: 'ignore' });
+      writer.addQuad(new Quad(
+        new NamedNode('a:a'),
+        new NamedNode('b:b'),
+        new NamedNode('c:c'),
+        new NamedNode('g:g')));
+      writer.end((error, output) => {
+        output.should.equal('<a:a> <b:b> <c:c>.\n');
+        done(error);
+      });
+    });
+
+    it('throws an graph-found error needed', done => {
+      const writer = new Writer({ graphs: 'error' });
+      writer.addQuad(new Quad(
+        new NamedNode('a:a'),
+        new NamedNode('b:b'),
+        new NamedNode('c:c'),
+        new NamedNode('g:g')), error => {
+        error.should.be.an.instanceof(Error);
+        error.should.have.property('message', 'The chosen serialization settings do not support triples in a non-default graph.');
+        done();
+      });
+    });
+
     it('should end when the end option is not set', done => {
       const outputStream = new QuickStream(), writer = new Writer(outputStream, {});
       outputStream.should.have.property('ended', false);