mongodb - 通过 _id 在 mongodb 数据库中的对象数组上查找

Question

我正在尝试在对象数组中查找对象的 ID。该 _id 与文档中的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)

我正在尝试像这样查找特定卡的 ID

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

但是我得到一个空的结果

我也试过

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

Answer 1

您可能需要使用 aggregate功能$unwind根据 _id 查找匹配卡片的卡片数组.

所以，用 Mongoose 代替 find使用 aggregate流水线

示例文档

> 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"}}] )

结果文档

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

如果你知道父_id，你可以进一步优化它, 在聚合管道中 $match由家长_id , 然后 $unwind , 然后 $match在阵列卡上 _id

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