N-blog CHAPTER #15: Reprint & Statistics

mongoose可以保存(save)空数组[], 但是默认不会保存空对象{}, 如果需要保存空对象,
要在mongoose.Schema里面设置选项options为{minimize: false}

mongoose的document._id不能被delete doc._id;, 虽然console.log(delete doc._id)返回true, 但是doc._id并没有被删除, 参考javascript delete
N-blog CHAPTER #16: Log