docs: document return types for .discriminator()

Fix #8287

lib/model.js

@@ -1067,6 +1067,7 @@ Model.exists = function exists(filter, options, callback) {
  * @param {String} name discriminator model name
  * @param {Schema} schema discriminator model schema
  * @param {String} [value] the string stored in the `discriminatorKey` property. If not specified, Mongoose uses the `name` parameter.
+ * @return {Model} The newly created discriminator model
  * @api public
  */
 
@@ -3411,7 +3412,7 @@ Model.bulkWrite = function(ops, options, callback) {
  *     var mongooseCandy = Candy.hydrate({ _id: '54108337212ffb6d459f854c', type: 'jelly bean' });
  *
  * @param {Object} obj
- * @return {Model} document instance
+ * @return {Document} document instance
  * @api public
  */
 

lib/queryhelpers.js

@@ -107,7 +107,7 @@ exports.getDiscriminatorByValue = getDiscriminatorByValue;
  * @param {Object} doc
  * @param {Object} fields
  *
- * @return {Model}
+ * @return {Document}
  */
 exports.createModel = function createModel(model, doc, fields, userProvidedFields) {
   model.hooks.execPreSync('createModel', doc);

lib/schema/SingleNestedPath.js

@@ -280,6 +280,7 @@ SingleNestedPath.prototype.doValidateSync = function(value, scope, options) {
  * @param {String} name
  * @param {Schema} schema fields to add to the schema for instances of this sub-class
  * @param {String} [value] the string stored in the `discriminatorKey` property. If not specified, Mongoose uses the `name` parameter.
+ * @return {Function} the constructor Mongoose will use for creating instances of this discriminator model
  * @see discriminators /docs/discriminators.html
  * @api public
  */

lib/schema/documentarray.js

@@ -147,6 +147,7 @@ function _createConstructor(schema, options, baseClass) {
  * @param {Schema} schema fields to add to the schema for instances of this sub-class
  * @param {String} [value] the string stored in the `discriminatorKey` property. If not specified, Mongoose uses the `name` parameter.
  * @see discriminators /docs/discriminators.html
+ * @return {Function} the constructor Mongoose will use for creating instances of this discriminator model
  * @api public
  */