Javascript 在MongoDB聚合管道中分解阵列

我想知道，当我还在MongoDB聚合管道中时，是否有可能对数组进行分解，这将使我的代码更加整洁

例如，我有以下聚合管道

await User.aggregate([
      { $match: { _id: userID } },
      {
        $project: { chatLogs: 1, username: 1, profilePicURL: 1 },
      },
      { $unwind: "$chatLogs" },
      {
        $lookup: {
          from: "users",
          let: { recipientID: "$chatLogs.recipientID" },
          pipeline: [
            {
              $match: { $expr: { $eq: ["$_id", "$$recipientID"] } },
            },
            { $project: { profilePicURL: 1 } },
          ],
          as: "chatLogs.recipientID",
        },
      },
    ]);

查询时会得到以下结果：

{
        "_id": "5f2ffb54eea9c2180a732afa",
        "username": "joe",
        "profilePicURL": "/images/profile/default_profile.png",
        "chatLogs": {
            "recipientID": [
                {
                    "_id": "5f2faf5ad18a76073729f475",
                    "profilePicURL": "/images/profile/default_profile.png"
                }
            ],
            "chat": "5f30b6c3d117441c2abda1ba"
        }
    }

在我的例子中，因为“recipientID”代表默认的MongoDB id，所以它总是唯一的。因此，我更喜欢下面的方法，其中得到的recipientID字段不再是一个无意义的数组

预期结果：

{
        "_id": "5f2ffb54eea9c2180a732afa",
        "username": "joe",
        "profilePicURL": "/images/profile/default_profile.png",
        "chatLogs": {
            "recipientID": {
                    "_id": "5f2faf5ad18a76073729f475",
                    "profilePicURL": "/images/profile/default_profile.png"
                }
            "chat": "5f30b6c3d117441c2abda1ba"
        }
    }

---

您可以在最后一个管道中使用

$unwind

解构

recipientID

数组

await User.aggregate([
      ... // your all pipelines

      // add this line
      { $unwind: "$chatLogs.recipientID" }
]);