如何查询和排序Mongoose子文档

Question

我需要在具有最低stats.reviewDate值的deck内部获取card。

例如，对以下内容的查询：

{
"_id": "608642db80a36336946620aa",
"cards": [
{
"stats": {
"reviewDate": "1985-03-26T04:34:17.425Z",
},
"_id": "6086430080a36336946620ab",
"front": "front",
"back": "back"
},
{
"stats": {
"reviewDate": "2021-05-26T04:34:17.425Z",
},
"_id": "6086430080a36336946620ab",
"front": "front",
"back": "back"
},
{
"stats": {
"reviewDate": "2021-04-26T04:34:17.425Z",
},
"_id": "6086430080a36336946620ab",
"front": "front",
"back": "back"
}
]
}

应返回：

{
"stats": {
"reviewDate": "1985-03-26T04:34:17.425Z",
},
"_id": "6086430080a36336946620ab",
"front": "front",
"back": "back"
}

我试图通过按降序对卡片进行排序，并读取列表中的第一项：来实现这一点

DeckModel.findById(req.params.deckId, 'cards')
.sort({'cards.stats.dateCreated': 'desc'})
.exec((err, docs) => {
if(err) { return next(err) }
console.log(docs.cards.[0]);
});

但它不起作用——当然是因为我对.sort((的理解不好(

这是一个与我相似的问题，尽管它没有被接受的答案。

如何构造一个返回所需结果的查询？

如果需要，下面是我的模式：

var DeckSchema = new Schema ( 
{
title: { type: String, required: true, maxlength: 255 },
cards: [CardSchema]
}
)

var CardSchema = new Schema(
{
stats: {
reviewDate: {type: Date, default: Date.now(), required: true},
},
front: String,
back: String
}
)

谢谢大家，

• Sour_Tooth

Answer 1

演示-https://mongoplayground.net/p/RUssJuB7XO2

db.collection.aggregate([
// { $match: {  } }, your query here
{ $unwind: "$cards" },
{ $sort: { "cards.stats.dateCreated": -1 } },
{ $limit: 1 },
{ $replaceRoot: { "newRoot": "$cards" } }
])