通过 _id 在 mongodb 数据库中的对象数组上查找

我正在尝试在对象数组中查找对象的 id。该 _id 与文档中其他字段具有相同的字段名称 _id。 这是我的模型（简要）

var CardSchema = new mongoose.Schema({
  beName: String,
  beLink: String,
  cards: [{ 
    cardType: String,
    cardBundle: String
  }]

这是我的数据库内容的示例

_id: ObjectId(5a52540638086448bf4235e8)
beName: Name1
beLink: Link1
cards: Array
 0: Object
    cardType: type1
    cardBundle: 1
    _id: ObjectId(5a526749d0ddab4bcdcc1556)
 1: Object
    cardType: type2
    cardBundle: 1
    _id: ObjectId(5a526749d0ddab4bcdcc1557)

...

_id: ObjectId(5a52540638086448bf4235e9)
beName: Namex
beLink: Linkx
cards: Array
 0: Object
    cardType: typex
    cardBundle: x
    _id: ObjectId(5a526749d0ddab4bcdcc1598)
 1: Object
    cardType: type2
    cardBundle: 1
    _id: ObjectId(5a526749d0ddab4bcdcc1599)

我正在尝试查找特定卡的 ID，如下所示

Cards.find({ _id: req.params.id}, function (err, post) {
    if (err) return next(err);
    res.json(post);
  });

但我得到一个空结果

我也尝试过

Cards.find({ _id: new ObjectId(req.params.id)}...

您可能需要使用aggregate功能为$unwind用于查找匹配卡的卡数组_id.

所以，在猫鼬中而不是find use aggregate管道

样本文档

> db.cards.findOne()
{
    "_id" : ObjectId("5a52f4136fe82b42b7439a21"),
    "beName" : "Name1",
    "beLink" : "Link1",
    "cards" : [
        {
            "cardType" : "type1",
            "cardBundle" : 1,
            "_id" : "5a52f3a66f112b42b7439a20"
        },
        {
            "cardType" : "type2",
            "cardBundle" : 1,
            "_id" : "5a52f3a66f112b42b7439a21"
        }
    ]
}

聚合函数

> db.cards.aggregate([{$unwind: "$cards"}, {$match:{"cards._id" : "5a52f3a66f112b42b7439a20"}}] )

结果文件

> db.cards.aggregate([{$unwind: "$cards"}, {$match:{"cards._id" : "5a52f3a66f112b42b7439a20"}}] ).pretty()
{
    "_id" : ObjectId("5a52f4136fe82b42b7439a21"),
    "beName" : "Name1",
    "beLink" : "Link1",
    "cards" : {
        "cardType" : "type1",
        "cardBundle" : 1,
        "_id" : "5a52f3a66f112b42b7439a20"
    }
}
> 

如果您了解父级，您可以进一步优化它_id，在聚合管道中$match由家长_id, then $unwind, then $match在阵列卡上_id

> db.cards.aggregate([{$match:{"_id":ObjectId("5a52f4136fe82b42b7439a21")}},{$unwind: "$cards"}, {$match:{"cards._id" : "5a52f3a66f112b42b7439a20"}}] )