Mongoose - 如何聚合两个集合中的内容

Question

我该如何使用 Mongoose 聚合操作呢？ 基本上，我有两个集合——“帖子”和“个人资料”。 一个名为“user”的用户 oid 是它们之间的共同引用。 我想使用“Post”中的 ID 从“Profile”中查找“handle”元素并汇总这些结果，以便将用户的句柄包含在响应中。

以下是我在查找单个帖子时能够做到这一点的方法：

// @route   GET api/posts/:id
// @desc    Get post by id
// @access  Public
router.get("/:id", (req, res) => {
  Post.findById(req.params.id)
    .then(post => {
      Profile.findOne({ user: post.user })
        .then(profile => res.json({ ...post._doc, userHandle: profile.handle }));
    })
    .catch(err => res.status(404).json({ "not found": err }));
});

但是，当我尝试将这种方法（使用映射操作）扩展到返回所有帖子的 GET 时，它变得不可行。

// @route   GET api/posts
// @desc    Get all the posts
// @access  Public
router.get("/", (req, res) => {
  Post.find()
    .sort({ date: -1 })
    .then(posts =>
      posts.map(
        post =>
          Profile.findOne({ user: post.user })
            .then(profile => (
              {
                ...JSON.parse(JSON.stringify(post)),
                userHandle: profile.handle
              }))
      ))
    .then(posts => res.json(posts))
    .catch(err => res.status(404).json({ "none found": err }));
});

换句话说，如果我有 发布：

{
    "_id": {
        "$oid": "5d1523b98d9dd16d832a8c5e"
    },
    "user": {
        "$oid": "5d1504e29dc0bd55461adca7"
    },
    "recipeName": "Pizza",
    "ingredients": "Flour and sauch"
}

和简介：

{
    "_id": {
        "$oid": "5d1505089dc0bd55461adca8"
    },
    "user": {
        "$oid": "5d1504e29dc0bd55461adca7"
    },
    "handle": "jack",
    "status": "Developer"
}

那么我真正想要的是这样的 JSON 对象（当我查询帖子时）： （注意“userHandle”现在存在）

{
    "_id": {
        "$oid": "5d1523b98d9dd16d832a8c5e"
    },
    "user": {
        "$oid": "5d1504e29dc0bd55461adca7"
    },
    "recipeName": "Pizza",
    "ingredients": "Flour and sauch",
    "userHandle": "jack"
}

我的 GET 需要返回这些帖子的整个数组。

Answer 1

Post.find().sort({date: -1}).then((posts) => {
  Post.populate(posts, [{
    path: 'user',
    select: {}, // projection
    model: User // User model
  }], (err, posts) => {
    if (err) return next(err);
    return res.json(posts);
  });
});

阅读更多关于猫鼬populate

编辑

如果不想每次都包含model，可以在Schema字段中添加ref（集合名称），它会自动指定型号！

示例：

const postSchema = Schema({
  ...
  user: { type: Schema.Types.ObjectId, ref: 'Users' }
});

Answer 2

getUserDetails: (request, response, next) => {
        try {
            let aggrQuery = [
                {
                    $lookup: {
                        from: "Profiles",
                        localField: "Id",//key name of common id in post collection as a reference
                        foreignField: "profileId",// key name of common id in profile collection
                        as: "userDetails"// handle element as well as other data in profile collection will be stored in userDetails
                    }
                },
                {
                    "$project": {
                       //we have to carry "_id", "ingredients","recipeName","user" of post collection for the next projection,and whole user information is stored in "userDetails"
                        "_id": 1,
                        "ingredients":1,
                        "recipeName":1,
                        "user":1,
                        userDetails : { $arrayElemAt : 
                      ["$userDetails", 0]}
                    }
                },
                {
                    "$project": {
                        //finally we prepare required data set for response,"_id", "ingredients","recipeName","user" of post collection,and only userHandle of Profiles from userDetails array(which contains all profile data)
                        "_id": "$_id",
                        "ingredients":"$ingredients",
                        "recipeName":"$recipeName",
                        "user":"$user",
                        "userDetails":{
                           "userHandle" :"$userDetails.userHandle",
                           "additionField1":"$userDetails.additionField1",
                           "additionField2":"$userDetails.additionField2",
                         }     
                    }
                }
            ]
            Post.aggregate(aggrQuery).exec((err, result) => {
                if(err){
                  response.json({
                      isError: true,
                      statuscode: 404,
                      details: null
                  })
                }
                else{
                   response.json({
                    isError: false,
                    statuscode: 200,
                    details: result
                  })
                }
            })
        }
        catch{
            response.json({
                isError: true,
                statuscode: 404,
                details: null
            });
        }
    },