聚合查询上的Mongodb填充字段

如何解决聚合查询上的Mongodb填充字段

我有这三个收藏集（产品，用户和评论）

1。产品型号

var ProductSchema = new Schema({
  title:          { type: String,text: true,required: true },description:    { type: String,category:       [{ type: String,required: true }],type:           [{ type: String,isUsed:         { type: Boolean,},manufacturer:   { type: String },price:          { type: Number },});

2。用户模型

var UserSchema = new Schema({
  firstName:      { type: String,lastName:       { type: String,country:        [{ type: String,phoneNumber:    [{ type: String,required: true }]
});

3。评论模型

var CommentSchema = new Schema({
  comment:        { type: String,commented_by:   { type: Schema.Types.ObjectId,ref: 'User',commented_on:   { type: Schema.Types.ObjectId,ref: 'Product',required: true }
});

然后，在发送获取特定产品的请求时，这是在后台运行的猫鼬代码。

      var aggregate = Product.aggregate([

        { "$match": { _id: ObjectId(req.params.id) } },/** which is the product id **/
        { "$limit": 1 },{ 
          $lookup: {
              from: 'comments',let: { id: "$_id" },pipeline: [
                { $match: { $expr: { $eq: [ "$commented_on.product","$$id" ] } } },],as: "comments"
            }
        },{ 
          $addFields: {
            comments: "$comments",comments_no: { $size: "$comments" },hasCommented: { $in: [ObjectId(req.user._id),"$comments.commented_by" ] },/** req.user._id  is the user's id **/
          }
        },{
            $project: {
              _id: 1,title: 1,description: 1,category: 1,type: 1,price: 1,comments: 1,hasCommented: 1,comments_no: 1,}
          }
      ]);

输出

{
    "_id": "5f992b5338f5f035f35911c5","title": "Some title here..."
    "description": Some description here ...
    "price": 1000,"category": "Clothing","type": "shoe","comments": [ 
        {
          "comment": "Nice Product","commented_by": "5f992b5338f5f035f35911b2","commented_on": "5f992b5338f5f035f35911c5"
        },{
          "comment": "I like this product","commented_by": "5f992b5338f5f035f35911a2",{
          "comment": "Great,I like it!","commented_by": "5f992b5338f5f035f35911c8","commented_on": "5f992b5338f5f035f35911c5"
        } 
                 
    ],"hasCommented": true,"comments_no": 3
}

预期结果

{
    "_id": "5f992b5338f5f035f35911c5","commented_by": { 
              "_id": "5f992b5338f5f035f35911b2","firstName": "Jack","lastName": "Sparrow" 
          },"commented_by": { 
              "_id": "5f992b5338f5f035f35911a2","firstName": "John","lastName": "Doe" 
          },"commented_by": { 
              "_id": "5f992b5338f5f035f35911c8","firstName": "Mary","lastName": "Jane" 
          },"comments_no": 3
}

获取特定产品时，我现在可以列出该产品的评论，但是问题出在“ commented_by”部分上所有列出的评论上，我需要填充它（需要firstName，lastName ...）字段

任何想法我该怎么做？

解决方法

您所做的是正确的。在Product和Comment之间进行查找之后，还需要进行另一个查找才能加入User。

您需要添加以下步骤来实现目标

• unwind以取消结构化comments[]数组
• lookup加入User集合
• 由于查找提供了一个数组，因此我们可以在安全运算符$arrayElemAt的帮助下使用$ifNull获取数组的第一个元素。 （如果comments []为空，则脚本将引发错误。为处理此问题，我们使用$ifNull）
• 我们已经取消了数组的结构，group帮助重新组合了数组

阶段在下面给出

  {
    $unwind: "$comments"
  },{
    $lookup: {
      from: "User",let: {
        id: "$comments.commented_by"
      },pipeline: [
        {
          $match: {
            $expr: {
              $eq: [
                "$_id","$$id"
              ]
            }
          }
        },],as: "comments.commented_by"
    }
  },{
    $addFields: {
      "comments.commented_by": {
        $ifNull: [
          {
            $arrayElemAt: [
              "$comments.commented_by",0
            ]
          },{}
        ]
      }
    }
  },{
    $group: {
      _id: "$_id",title: {
        $first: "$title"
      },hasCommented: {
        $first: "$hasCommented"
      },comments: {
        $push: "$comments"
      }
    }
  }

工作Mongo playground

注意：仅供参考，变量和集合名称可能不同。