moved query.js createModel private to queryhelpers.js for use in hydr…

…ating models in streams. fixes #1792

lib/query.js

@@ -1038,40 +1038,14 @@ function completeMany (model, docs, fields, self, pop, promise) {
     { populated: pop }
     : undefined;
   for (var i=0; i < len; ++i) {
-    arr[i] = createModel(model, docs[i], fields);
+    arr[i] = helpers.createModel(model, docs[i], fields);
     arr[i].init(docs[i], opts, function (err) {
       if (err) return promise.error(err);
       --count || promise.complete(arr);
     });
   }
 }
 
-/*!
- * If the document is a mapped discriminator type, it returns a model instance for that type, otherwise,
- * it returns an instance of the given model.
- *
- * @param {Model} model
- * @param {Object} doc
- * @param {Object} fields
- *
- * @return {Model}
- */
-function createModel(model, doc, fields) {
-    var discriminatorMapping = model.schema
-        ? model.schema.discriminatorMapping
-        : null;
-
-    var key = discriminatorMapping && discriminatorMapping.isRoot
-      ? discriminatorMapping.key
-      : null;
-
-    if (key && doc[key] && model.discriminators && model.discriminators[doc[key]]) {
-        return new model.discriminators[doc[key]](undefined, fields, true);
-    }
-
-    return new model(undefined, fields, true);
-}
-
 /**
  * Declares the query a findOne operation. When executed, the first found document is passed to the callback.
  *
@@ -1406,7 +1380,7 @@ function completeOne (model, doc, fields, self, pop, promise) {
     { populated: pop }
     : undefined;
 
-  var casted = createModel(model, doc, fields)
+  var casted = helpers.createModel(model, doc, fields)
   casted.init(doc, opts, function (err) {
     if (err) return promise.error(err);
     promise.complete(casted);

lib/queryhelpers.js

@@ -40,6 +40,32 @@ exports.preparePopulationOptionsMQ = function preparePopulationOptionsMQ (query,
   return pop;
 }
 
+/*!
+ * If the document is a mapped discriminator type, it returns a model instance for that type, otherwise,
+ * it returns an instance of the given model.
+ *
+ * @param {Model}  model
+ * @param {Object} doc
+ * @param {Object} fields
+ *
+ * @return {Model}
+ */
+exports.createModel = function createModel(model, doc, fields) {
+  var discriminatorMapping = model.schema
+    ? model.schema.discriminatorMapping
+    : null;
+
+  var key = discriminatorMapping && discriminatorMapping.isRoot
+    ? discriminatorMapping.key
+    : null;
+
+  if (key && doc[key] && model.discriminators && model.discriminators[doc[key]]) {
+    return new model.discriminators[doc[key]](undefined, fields, true);
+  }
+
+  return new model(undefined, fields, true);
+}
+
 /*!
  * Set each path query option to lean
  *

lib/querystream.js

@@ -232,7 +232,8 @@ QueryStream.prototype._onNextObject = function _onNextObject (err, doc) {
 }
 
 function createAndEmit (self, doc) {
-  var instance = new self.query.model(undefined, self._fields, true);
+  var instance = helpers.createModel(self.query.model, doc, self._fields);
+
   instance.init(doc, function (err) {
     if (err) return self.destroy(err);
     emit(self, instance);

test/model.discriminator.querying.test.js

@@ -119,6 +119,49 @@ describe('model', function() {
           });
         });
       });
+
+      it('hydrates streams', function(done) {
+        var baseEvent  = new BaseEvent({ name: 'Base event' });
+        var impressionEvent = new ImpressionEvent({ name: 'Impression event' });
+        var conversionEvent = new ConversionEvent({ name: 'Conversion event', revenue: 1.337 });
+
+        baseEvent.save(function(err) {
+          assert.ifError(err);
+          impressionEvent.save(function(err) {
+            assert.ifError(err);
+            conversionEvent.save(function(err) {
+              assert.ifError(err);
+              var stream = BaseEvent.find({}).sort('name').stream();
+
+              stream.on('data', function(doc) {
+                switch(doc.name) {
+                  case 'Base event':
+                    assert.ok(doc instanceof BaseEvent);
+                    break;
+                  case 'Impression event':
+                    assert.ok(doc instanceof BaseEvent);
+                    assert.ok(doc instanceof ImpressionEvent);
+                    break;
+                  case 'Conversion event':
+                    assert.ok(doc instanceof BaseEvent);
+                    assert.ok(doc instanceof ConversionEvent);
+                    break;
+                  default:
+
+                }
+              });
+
+              stream.on('error', function (err) {
+                assert.ifError(err);
+              });
+
+              stream.on('close', function() {
+                done();
+              });
+            });
+          });
+        });
+      });
     });
 
     describe('findOne', function() {