如何从 mongodb 查询和获取数组中的一项？

Question

我是 MongoDB/Mongoose 的新手，我正在使用 MongoDB、Node 和 Express 如何从 mongodb 查询和获取数组中的一项？

这是数据库结构

{
       "_id" : ObjectId("5e19d76fa45abb5d4d50c1d3"),
       "name" : "Leonel Messi",
       "country" : "Argentina",
       "awards" : [ "Ballon d'Or", "Golden Boot", "FIFA World Player of the Year",]
}

这是在node js环境中使用mongoose和express的查询

router.get('/FindPlayers', async (req, res) => {

const player = await Players.findOne({ name: "Leonel Messi" }, { country: 1, awards: [0], _id: 0, });

  res.send(player);
});

我想得到县和奖项数组中的第一项，如下所示

{
  country : "Argentina",
  awards : [ "Ballon d'Or" ]
}

但是我得到了

{
  country : "Argentina",
  awards : [ 0 ]
}

Answer 1

试试这个：

const player = await Players.findOne(
    {
        name: "Leonel Messi"
    },
    {
        country: 1,
        awards: { $arrayElemAt: ["$awards", 0] },
        _id: 0
    }
);

// or

const player = await Players.findOne(
    {
        name: "Leonel Messi"
    },
    {
        country: 1,
        awards: { $first: "$awards" },
        _id: 0
    }
);