MongoDB

Question

我有 2 个使用简单嵌套数组的集合。记录示例如下所示：

菜单

{ 
    "_id" : ObjectId("620323fe80ec16abea7a0205"), 
    "name" : "A new menu", 
    "description" : "", 
    "menuData" : [
        {
            "catName" : "Cat 2", 
            "items" : [
                "61ded42461b1d8966c5efc45", 
                "61ded55001e3cafb8db19198", 
                "61df9adf2441b6113033f341", 
                "61dfa8c82441b6113033f738"
            ]
        }, 
        {
            "catName" : "Cat 1", 
            "items" : [
                "62020691adda4aab89f1742d", 
                "61dfa8c82441b6113033f738"
            ]
        }
    ], 
    "status" : "active", 
}

并且我正在尝试完成对菜单项数组 (menuData.items) 的查找。这些是来自另一个集合的对象 ID。

菜单项 一个例子是：

{ 
    "_id" : ObjectId("61ded55001e3cafb8db19198"), 
    "name" : "Coca-Cola 600ml", 
    "description" : "Refreshing taste...ahhh", 
    "price" : 3.95, 
    "tags" : [
        "drinks"
    ], 
    "options" : [

    ], 
    "status" : "active",  
}

使用以下聚合，我没有得到查找的输出

db.getCollection("menus").aggregate(
[
    { 
        "$match" : { 
            "_id" : ObjectId("620323fe80ec16abea7a0205")
        }
    }, 
    { 
        "$addFields" : { 
            "newField" : "$menuData.items"
        }
    }, 
    { 
        "$unwind" : { 
            "path" : "$newField"
        }
    }, 
    { 
        "$lookup" : { 
            "from" : "menuitems", 
            "localField" : "newField", 
            "foreignField" : "_id", 
            "as" : "items"
        }
    }
]
);

输出

{ 
    "_id" : ObjectId("620323fe80ec16abea7a0205"), 
    "name" : "A new menu", 
    "description" : "", 
    "menuData" : [
        {
            "catName" : "Cat 2", 
            "items" : [
                "61ded42461b1d8966c5efc45", 
                "61ded55001e3cafb8db19198", 
                "61df9adf2441b6113033f341", 
                "61dfa8c82441b6113033f738"
            ]
        }, 
        {
            "catName" : "Cat 1", 
            "items" : [
                "62020691adda4aab89f1742d", 
                "61dfa8c82441b6113033f738"
            ]
        }
    ], 
    "status" : "active", 
    "createdBy" : ObjectId("61bb07c778e39ca45c161d81"), 
    "createdByModel" : "Administrator", 
    "createdAt" : ISODate("2022-02-09T02:16:30.108+0000"), 
    "updatedAt" : ISODate("2022-02-09T04:26:00.837+0000"), 
    "__v" : NumberInt(0), 
    "newField" : [
        "61ded42461b1d8966c5efc45", 
        "61ded55001e3cafb8db19198", 
        "61df9adf2441b6113033f341", 
        "61dfa8c82441b6113033f738"
    ], 
    "items" : [

    ]
}

如您所见，项目是空的。我尝试在没有 $addFields 和 $unwind 的情况下完成此操作 - 结果相同。

非常感谢任何帮助。

Answer 1

你需要$lookup with pipeline.

将 ObjectId 转换为字符串（newFields 保存一组 Id 字符串，而 menuItems 文档 Id 是一个 ObjectId）
通过 $in 检查转换后的 id 字符串是否在 newFields 数组中。

{
  "$lookup": {
    "from": "menuitems",
    let: {
      newField: "$newField"
    },
    pipeline: [
      {
        $match: {
          $expr: {
            $in: [
              {
                $toString: "$_id"
              },
              "$$newField"
            ]
          }
        }
      }
    ],
    "as": "items"
  }
}

Sample Demo on Mongo Playground

MongoDB - 与嵌套数组的聚合不起作用

MongoDB - Aggregate with nested array not working

javascript

node.js

aggregation-framework