MongoDB 多连接子文档

Question

我有两个 collections，

用户集合：

{
    "userId": 1,
    "name": 'John',
    "profile": 'john.png'
},
{
    "userId": 2,
    "name": 'Doe',
    "profile": 'doe.png'
},
{
    "userId": 3,
    "name": 'John Doe',
    "profile": 'johndoe.png'
}

帖子集合：

{
    "postId": 1,
    "userId": 1,
    "postContent": "Lorem Ipsum is simply dummy text of the printing and typesetting industry.",
    "comments": [
        {
            "comment": "sample comment",
            "commentedBy": 2,
        },
        {
            "comment": "Another sample comment",
            "commentedBy": 3,
        }
    ],
}

如何通过 mongoose 中的单个查询获取帖子详细信息，包括单个帖子的用户详细信息和个人评论的用户详细信息？

Answer 1

您可能想要使用 Mongoose 提供的“填充”方法： https://mongoosejs.com/docs/populate.html

它允许您在架构定义中“链接”您的 collections，并在单个查询中查询和填充所有相关的 collections，例如

Posts.findOne({ postId: 1 }).populate('user')

按照上面的文档链接了解有关如何编写模式的更多详细信息。

Answer 2

您可以使用$aggregate和$lookup来执行此类

db.posts.aggregate(
  [
    {
      $lookup:
      {
        from: "users",
        localField: "userId",
        foreignField: "userId",
        as: "users"
      }
    }
  ]
).pretty()

这将打印如下

{
        "_id" : ObjectId("5ecceb468d4390391825b79d"),
        "postId" : 1,
        "userId" : 1,
        "postContent" : "Lorem Ipsum is simply dummy text of the printing and typesetting industry.",
        "comments" : [
                {
                        "comment" : "sample comment",
                        "commentedBy" : 2
                },
                {
                        "comment" : "Another sample comment",
                        "commentedBy" : 3
                }
        ],
        "users" : [
                {
                        "_id" : ObjectId("5ecceb168d4390391825b79a"),
                        "userId" : 1,
                        "name" : "John",
                        "profile" : "john.png"
                }
        ]
}

参考来自 MongoDB

https://docs.mongodb.com/manual/reference/operator/aggregation/lookup/