Question

我有两种不同的模型：

促销
标签

每个促销都有一个字段，其中包含对标记ID的引用。这在我的架构中引用并且工作正常：

const PromotionSchema = mongoose.Schema({
    tags: { type: mongoose.Schema.Types.ObjectId, ref: 'Tag' }
}, { collection: 'promotions' });

我的问题是如何创建自定义响应，按标记对所有促销进行分组？像这样：

{ 
   "tag": {
     "_id": "999",
     "value": "Lorem Ipsum"
   },
   "promotions": [{
      "_id": "0001",
      "value": "Value of promotion Nº1"
   },
   {
      "_id": "0002",
      "value": "Value of promotion Nº2"
   },
    ... And the others that have the same Tag ID assigned
   ]}
}

现在，我正在使用Vanilla Javascript获取所有促销和过滤功能。我需要知道如何使用Mongoose来改善这一点。

Answer 1

您可以尝试以下聚合函数来实现结果......

如果你有mongodb版本 3.6

db.promotion.aggregate([
  // stage 1
  { "$lookup": {
    "from": Promotions.collection.name,
    "let": { "tags": "$tags" },
    "pipeline": [
       { "$match": { "$expr": { "$eq": [ "$_id", "$$tags" ] } } }
     ],
     "as": "tags"
  }},
  // stage 2
  { "$addFields": { 
    "tags": { "$arrayElemAt": [ "$tags", 0 ] }
  }},
  // stage 3
  { "$group": {
    "_id": "$tags._id",
    "promotions": {
        "$push": {
            "fieldName1": "$fieldName1",
            "fieldName2": "$fieldName2",
        }
    }
  }}
 ])

如果你有 3.6 之前的mongodb版本

db.promotion.aggregate([
  { "$lookup": {
    "from": Promotions.collection.name,
    "localField": "tags",
    "foreignField": "_id"
     "as": "tags"
  }},
  { "$unwind": "tags" },
  { "$group": {
    "_id": "$tags._id",
    "promotions": {
        "$push": {
            "fieldName1": "$fieldName1",
            "fieldName2": "$fieldName2",
        }
    }
  }}
 ])

两者都会提供类似的输出

{ 
   "tag": {
     "_id": "999",
     "value": "Lorem Ipsum"
   },
   "promotions": [{
      "_id": "0001",
      "value": "Value of promotion Nº1"
   },
   {
      "_id": "0002",
      "value": "Value of promotion Nº2"
   }
   ]}
}

在mongodb中查找外部字段的组

1 个答案: