Mongoose aggregate从另一个集合中获取多个记录中的相似项之和

Question

我需要从用户的所有帖子中获得喜欢字段的总数
这里是模式
用户模式

    {
        "_id": "5f5b784209393b0638f896e2",
        "name": "Test User",
        "avatar": "https://someurl/attachments/media-6489.PNG"
    }

发布架构

    {
        "likes": [
            "5f4d553370eef30017288fb0",    // other users who liked the post
            "5f4fad6cc7d4990017fb0d29",
            "5f5a3c074de2d1246c99767b",
            "5f5b790532dd2f1de4127aa4",
            "5f5c6aeff8170922d44eeb7a"
        ],
        "_id": "5f65daf13ce59d0a5482ea0d",
        "text": "fdsa",
        "author": "5f5b784209393b0638f896e2",
    }

我是新来的猫鼬，提前感谢...

Answer 1

终于完成了这个查询

const postsData = await User.aggregate([
    { $match: { _id: mongoose.Types.ObjectId(req.user.id) } },
    {
        $lookup: {
            from: "posts",
            localField: "_id",
            foreignField: "author",
            as: "posts",
        }
    },
    { $unwind: "$posts", },
    {
        $group: {
            _id: "$_id",
            likes: { $sum: { $size: "$posts.likes" } }
        }
    },
]);