从两个数据库集合（Mongoose/MongoDB）中查询和匹配答案

【问题标题】：Query and Match from Two Database Collections (Mongoose/MongoDB)从两个数据库集合（Mongoose/MongoDB）中查询和匹配
【发布时间】：2021-09-27 23:06:09
【问题描述】：

我需要帮助创建一个 mongoose 查询，该查询在用户集合中找到请求用户的喜欢，然后在帖子集合中搜索用户的喜欢。希望有人能告诉我我在查询中做错了什么，或者我怎样才能做得更好。

用户和帖子集合：

const users = [
{
  _id: "1",
  likes: ["1", "2"]
},
{
  _id: "2",
  likes: ["3"]
}
]

const posts = [
{
  _id: "1",
  stuff: "stuff1"
},
{
  _id: "2",
  stuff: "stuff2"
},
{
  _id: "3",
  stuff: "stuff3"
}
]

聚合查询：

router.post("/", authUser, async (req, res) => {
  User.aggregate([
    {
      $match: {
        _id: ObjectId(req.user._id), //user 1
      },
    },
    {
      $unwind: "$likes",
    },
    {
      $lookup: {
        from: "posts",
        let: { like: "$likes" },
        pipeline: [
          {
            $match: {
              $expr: {
                $eq: ["_id", "$$like"],
              },
            },
          },
        ],
        as: "matched_posts",
      },
    },
    {
      $unwind: "$matched_posts",
    },
  ]).then((d) => {
    console.log(d);
  });
});

期望的输出：

const output = [
{
  _id: "1",
  stuff: "stuff1"
},
{
  _id: "2",
  stuff: "stuff2"
}
]

【问题讨论】：

标签： mongodb express mongoose aggregation-framework

【解决方案1】：

$match你的条件
$lookup 与帖子集合，传递 likes 作为 localField 和 _id 作为 foreignField
$unwind解构likes数组
$replaceRoot 替换 likes 对象

router.post("/", authUser, async (req, res) => {
  User.aggregate([
    { $match: { _id: ObjectId(req.user._id) } },
    {
      $lookup: {
        from: "posts",
        localField: "likes",
        foreignField: "_id",
        as: "likes"
      }
    },
    { $unwind: "$likes" },
    { $replaceRoot: { newRoot: "$likes" } }
  ])
  .then((d) => {
    console.log(d);
  });
});

Playground

【讨论】：