mongodb query returns [object Object]

I'm using mongo with NODEJS, but while trying to get data from db, there is always an object it returns [object Object] instead of object; Here is my Schema

IngredientSchema = new MongoDb.Schema(
    {
        "name": String  //名称
        ,"optional":Boolean
        ,"substitution": String
        ,"preparation": String
        , "amount": Number
        , "units": String   //单位
    }
);

directionSchema = new MongoDb.Schema(
    {
        "image": String     //图片
        ,"tip": String
        , "content": String //正文
        , "duration": Number    //定时 无定时则设置为null
        , "audiopath": String
    }
);

infoSchema =  {
    "title": String //菜谱名称
    ,"lang": String
    ,"author":String
    ,"image_url": String
    ,"serves": Number
    ,"source": String
    ,"time":Number
};

categorySchema = {
    "region": String
    ,"type": String
    ,"tags": String
};

CookBookSchema= new MongoDb.Schema(
    {
        "info": infoSchema
        , "categories": categorySchema
        , "ingredients": [IngredientSchema] //材料
        , "directions": [directionSchema]       //步骤
        ,'nutrition':String
    }
    , {strict: false}
);
CookBook= MongoDb.model(COOKBOOK_TABLE, CookBookSchema);

it returns value like this

[
    {
        "categories": "[object Object]",
        ....
    }
]

The other object in result works fine. I searched in google but can't find the answer

In mongodb the "categories" data is like this

categories" : { "type" : "cake", "tags" : "Cake, Caramel Sauce, Chocolate Cake, Chocolate Cake, Chocolate Desserts, Christmas, Christmas Cake, Christmas Desserts, Christmas Party, Coconuts, Desserts, Fruit, German Chocolate Cake, Healthy Cooking, Ice Cream Toppings, Low Sodium, More Fruits, More Holidays, Sauces and Toppings, Valentine's Day" }

But it lack of an _id object which other objects will have

i wrote into mongodb using codes below

```

cookBookModule.create(data, function(err, object) {
            if (err) {
                console.error(err);
                console.log(data);
                return res.status(HTTPCODE.DB_ERR).json('save failed');
            }

            res.status(HTTPCODE.CREATED).json(object);
            TtsModule.audio_process(object);
        })

```

Is there anything wrong?