如何合并来自两个不同集合的文档

Question

如何合并来自两个不同集合的文档。

从shopping_collection我们可以获得购买历史，

为了获得每个购买历史的详细信息，我需要从detailed_shopping_list_collection 获得信息

但aggregate似乎不可能做到这一点，因为集合不同？

如何使用mapreduce获取它？

shopping_collection

{
  "name": "Mary",
  "gender": "M",
  "birthday": new Date("1980-04-01T08:00:00+0800"),
  "records": [
    {
      "BUY_DATE": new Date("1996-02-08T08:00:00+0800"),
      "SEQ_NO": 768,
    },
    {
      "BUY_DATE": new Date("1996-02-06T08:00:00+0800"),
      "SEQ_NO": 595,
    }
}

详细_跳跃列表_集合

{
  "BUY_DATE": new Date("1996-02-08T08:00:00+0800"),
  "SEQ_NO": 768
  "ITEM_NAME": "iphone4s"
  "PRICE": 500
},
{
  "BUY_DATE": new Date("1996-02-08T08:00:00+0800"),
  "SEQ_NO": 768
  "ITEM_NAME": "iphone4s"
  "PRICE": 500
},
{
  "BUY_DATE": new Date("1996-02-08T08:00:00+0800"),
  "SEQ_NO": 768
  "ITEM_NAME": "macbook"
  "PRICE": 700
}

预期汇总结果

{
  "name": "Mary",
  "gender": "M",
  "birthday": new Date("1980-04-01T08:00:00+0800"),
  "records": [
    {
      "BUY_DATE": new Date("1996-02-08T08:00:00+0800"),
      "SEQ_NO": 768,
      "PURCHASE_HISTORY":[
        {"ITEM_NAME": "iphone4s"
                "PRICE": 500},
        {"ITEM_NAME": "iphone4s"
                "PRICE": 500},                
        {"ITEM_NAME": "macbook"
                    "PRICE": 700}
      ]
      "UNIQUE_PURCHASE_ITEMS":[ "iphone4s", "macbook"
      ]
    },
    {
      "BUY_DATE": new Date("1996-02-06T08:00:00+0800"),
      "SEQ_NO": 595,
    }
}

Answer 1

您试图实现的目标应该在客户端使用多个查询来完成，因为mapreduce不能代替联接。然而，一些人提出了一些有趣的方法，例如。http://tebros.com/2011/07/using-mongodb-mapreduce-to-join-2-collections/.

Answer 2

请检查以下查询：

// MAP FUNCTION LOGIC 
var map = function(){
 var arr = new Array();
 this.records.forEach(function(doc){ 
   var temp = db.detailed_shopping_list_collection.find(
       {"BUY_DATE": doc.BUY_DATE, "SEQ_NO" : doc.SEQ_NO}); 
   arr.push(temp); 
                 });
 emit(this._id,{"name" : this.name, "gender" :
  this.gender, "birthday" :   this.birthday, "records" : arr );
}

// REDUCE FUNCTION LOGIC
var reduce = function(id , doc){ return doc; }

// MAP REDUCE CALL
db.shopping_collection.mapReduce( map,reduce,{out: {inline :1}} );