Question

我是mongo的新手，我试图通过子文档中的值获取组，并使用mongo集合结构：

Exception in thread "main" java.lang.StringIndexOutOfBoundsException:    String index out of range: 29
 at java.lang.String.charAt(String.java:686)
at EncryptDecrypt.encrypt(EncryptDecrypt.java:14)
at EncryptDecrypt.main(EncryptDecrypt.java:28)

在这里，我想在此进行分组。例如在mysql中：

{
"_id" : ObjectId("589d4e4b270f8b1635d400b1"),
"myShopId" : 439,
"products" : [ 
    {
        "productId" : "1234",
        "productName" : "sambarpowder 500 gm",
        "productCategory" : "masala",           
        "mrp" : "90",           
        "_id" : ObjectId("589d595f6da20b72fe006ea9")
    }, 
    {
        "productId" : "5678",
        "productName" : "moong dhal 200 gms",            
        "productCategory" : "dhal",            
        "mrp" : "38 ",
        "_id" : ObjectId("589d595f6da20b72fe006eaa")
    },
      {
        "productId" : "5678",
        "productName" : "moong dhal 200 gms",            
        "productCategory" : "dhal",            
        "mrp" : "38 ",
        "_id" : ObjectId("589d595f6da20b72fe006eaa")
    }
],
"isAlive" : 1,
"__v" : 3
}

如何在mongo子文档中实现该组

select productCategory from products where shopId = '439' groupby productCategory

Answer 1

希望这会有所帮助，

  db.test.aggregate([{
    $match: {
      myShopId: 439
    }
  }, {
    $unwind: "$products"
  }, {
    $group: {
      _id: {
        "productCategory": "$products.productCategory"
      },
      "id": {
        $first: "$products._id"
      }
    }
  }])

输出：

{＆＃34; _id＆＃34; ：{＆＃34; productCategory＆＃34; ：＆＃34; dhal＆＃34; }，＆＃34; id＆＃34; ：ObjectId（＆＃34; 589d595f6da20b72fe006eaa＆＃34;）}

{＆＃34; _id＆＃34; ：{＆＃34; productCategory＆＃34; ：＆＃34; masala＆＃34; }，＆＃34; id＆＃34; ：ObjectId（＆＃34; 589d595f6da20b72fe006ea9＆＃34;）}

如何分组mongo子文件

1 个答案: