全文搜索在mlab中不起作用

Question

我尝试使用link这样的全文搜索功能
但是当我尝试localhost:3000/motel/full-search-test/h时返回

  

没有结果

我使用mlab在线存储数据库，它可用于除此功能以外的所有功能。我怎么解决这个问题？
我的模特：

var mongoose = require("mongoose"); //
var Schema = mongoose.Schema; //
var motelSchema = new Schema({
_creator:       { type: Schema.Types.ObjectId, ref: 'User' },
add:            String,
address:        String,
area:           { type: Number, default: 0},
category:       String,
city:           String,
contact:        String,
created_at:     {required: true, type: Date, default: new Date()},
customer:       String,
description:    String,
district:       String,
fields:         { type: [String], index: true, text: true },
img:            {type: [String]},
lng:            String,
lat:            String,
price:          { type: String, default: "Thỏa thuận"},
rating:         {type: Number, default: 4.75},
status:         { type: Number, default: 0},
street:         String,
title:          { type: String, required: true },
ward:           String
},{collection : 'motels'});
motelSchema.set('autoIndex', false); // prevent mlab autoindex

motelSchema.index({'$**': 'text'});

var motels  = mongoose.model("motels", motelSchema);
module.exports = motels;

我的服务：
    service.test = test;
    module.exports = service;

function test(searchString) {
    var deferred = Q.defer();

    motels.find({$text: {$search: searchString}})
    .skip(20)
    .limit(10)
    .exec(function(err, motels) {
        if(err) { 
            deferred.reject(err);
        }
        deferred.resolve(motels);
     });
    return deferred.promise;     
}