Implemented hasNext for simpler iteration when using genertors

Author: christkv

lib/cursor.js

@@ -120,6 +120,8 @@ var Cursor = function(bson, ns, cmd, options, topology, topologyOptions) {
     , topologyOptions: topologyOptions
     // Promise library
     , promiseLibrary: promiseLibrary 
+    // Current doc
+    , currentDoc: null
   }
 
   // Legacy fields
@@ -166,12 +168,71 @@ for(var name in CoreCursor.prototype) {
   Cursor.prototype[name] = CoreCursor.prototype[name];
 }
 
+/**
+ * Check if there is any document still available in the cursor
+ * @method
+ * @param {Cursor~resultCallback} callback The result callback.
+ * @throws {MongoError}
+ * @deprecated
+ * @return {Promise} returns Promise if no callback passed
+ */
+Cursor.prototype.hasNext = function(callback) {
+  var self = this;
+
+  // Execute using callback
+  if(typeof callback == 'function') return nextObject(self, function(err, doc) {
+    if(!doc) return callback(null, false);
+    self.s.currentDoc = doc;
+    callback(null, true);
+  });
+
+  // Return a Promise
+  return new this.s.promiseLibrary(function(resolve, reject) {
+    nextObject(self, function(err, doc) {
+      if(self.s.state == Cursor.CLOSED || self.isDead()) return resolve(false);
+      if(err) return reject(err);
+      if(!doc) return resolve(false);
+      self.s.currentDoc = doc;
+      resolve(true); 
+    });
+  });
+}
+
+
+/**
+ * Get the next available document from the cursor, returns null if no more documents are available.
+ * @method
+ * @param {Cursor~resultCallback} callback The result callback.
+ * @throws {MongoError}
+ * @deprecated
+ * @return {Promise} returns Promise if no callback passed
+ */
 Cursor.prototype.next = function(callback) {
   var self = this;
-  if(typeof callback == 'function') return this._next(callback);
+
+  // Execute using callback
+  if(typeof callback == 'function') {
+    // Return the currentDoc if someone called hasNext first
+    if(self.s.currentDoc) {
+      var doc = self.s.currentDoc;
+      self.s.currentDoc = null;
+      return callback(null, doc);
+    }
+
+    // Return the next object
+    return nextObject(self, callback)
+  };
+
   // Return a Promise
   return new this.s.promiseLibrary(function(resolve, reject) {
-    self._next(function(err, r) {
+    // Return the currentDoc if someone called hasNext first
+    if(self.s.currentDoc) {
+      var doc = self.s.currentDoc;
+      self.s.currentDoc = null;
+      return resolve(doc);
+    }
+
+    nextObject(self, function(err, r) {
       if(err) return reject(err);
       resolve(r); 
     });
@@ -360,15 +421,7 @@ Cursor.prototype.skip = function(value) {
  * The callback format for results
  * @callback Cursor~resultCallback
  * @param {MongoError} error An error instance representing the error during the execution.
- * @param {(object|null)} result The result object if the command was executed successfully.
- */
-
-/**
- * Get the next available document from the cursor, returns null if no more documents are available.
- * @function external:CoreCursor#next
- * @param {Cursor~resultCallback} callback The result callback.
- * @throws {MongoError}
- * @return {Promise} returns Promise if no callback passed
+ * @param {(object|null|boolean)} result The result object if the command was executed successfully.
  */
 
 /**
@@ -433,20 +486,7 @@ Cursor.prototype.skip = function(value) {
  * @deprecated
  * @return {Promise} returns Promise if no callback passed
  */
-Cursor.prototype.nextObject = function(callback) {
-  var self = this;
-
-  // Execute using callback
-  if(typeof callback == 'function') return nextObject(self, callback);
-
-  // Return a Promise
-  return new this.s.promiseLibrary(function(resolve, reject) {
-    nextObject(self, function(err, r) {
-      if(err) return reject(err);
-      resolve(r); 
-    });
-  });
-}
+Cursor.prototype.nextObject = Cursor.prototype.next;
 
 var nextObject = function(self, callback) {
   if(self.s.state == Cursor.CLOSED || self.isDead()) return handleCallback(callback, new MongoError("Cursor is closed"));

test/functional/operation_example_tests.js

@@ -5354,6 +5354,84 @@ exports.shouldCorrectlyPeformNextObjectOnCursor = {
   }
 }
 
+/**
+ * A simple example showing the use of next.
+ *
+ * @example-class Cursor
+ * @example-method next
+ * @ignore
+ */
+exports.shouldCorrectlyPeformNextOnCursorWithCallbacks = {
+  // Add a tag that our runner can trigger on
+  // in this case we are setting that node needs to be higher than 0.10.X to run
+  metadata: { requires: { topology: ['single', 'replicaset', 'sharded', 'ssl', 'heap', 'wiredtiger'] } },
+  
+  // The actual test we wish to run
+  test: function(configuration, test) {
+    var db = configuration.newDbInstance(configuration.writeConcernMax(), {poolSize:1, auto_reconnect:false});
+
+    db.open(function(err, db) {
+    // LINE var MongoClient = require('mongodb').MongoClient,
+    // LINE   test = require('assert');
+    // LINE MongoClient.connect('mongodb://localhost:27017/test', function(err, db) {
+    // REPLACE configuration.writeConcernMax() WITH {w:1}
+    // REMOVE-LINE restartAndDone
+    // REMOVE-LINE test.done();
+    // BEGIN
+
+      // Create a collection
+      var collection = db.collection('simple_next_object_collection_with_next');
+
+      // Insert some documents we can sort on
+      collection.insertMany([{a:1}, {a:2}, {a:3}], configuration.writeConcernMax(), function(err, docs) {
+        test.equal(null, err);
+
+        // Do normal ascending sort
+        var cursor = collection.find();
+        // Perform hasNext check
+        cursor.hasNext(function(err, r) {
+          test.equal(null, err);
+          test.ok(r);
+
+          cursor.next(function(err, r) {
+            test.equal(null, err);
+            test.equal(1, r.a);
+
+            cursor.hasNext(function(err, r) {
+              test.equal(null, err);
+              test.ok(r);
+
+              cursor.next(function(err, r) {
+                test.equal(null, err);
+                test.equal(2, r.a);
+
+                cursor.hasNext(function(err, r) {
+                  test.equal(null, err);
+                  test.ok(r);
+
+                  cursor.next(function(err, r) {
+                    test.equal(null, err);
+                    test.equal(3, r.a);
+
+                    cursor.hasNext(function(err, r) {
+                      test.equal(null, err);
+                      test.ok(!r);
+
+                      db.close();
+                      test.done();
+                    });
+                  });
+                });
+              });
+            });
+          });
+        });
+      });
+    });
+    // END
+  }
+}
+
 /**
  * A simple example showing the use of the cursor explain function.
  *

test/functional/operation_generators_example_tests.js

@@ -4348,7 +4348,7 @@ exports.shouldCorrectlyPeformNextObjectOnCursorWithGenerators = {
  * A simple example showing the use of next and co module to iterate over cursor
  *
  * @example-class Cursor
- * @example-method nextObject
+ * @example-method next
  * @ignore
  */
 exports.shouldCorrectlyPeformNextOnCursorWithGenerators = {
@@ -4386,11 +4386,12 @@ exports.shouldCorrectlyPeformNextOnCursorWithGenerators = {
       var doc = null;
       var docs = [];
 
-      // Iterate over all the cursor items
-      while((doc = yield cursor.next()) != null) {
-        docs.push(doc);
+      // Iterate over the cursor
+      while(yield cursor.hasNext()) {
+        docs.push(yield cursor.next());
       }
 
+      // Validate the correct number of elements
       test.equal(3, docs.length);
       db.close();
       test.done();