如何编写 Mongodb 查询来计算集合行数

Question

我正在努力实现以下目标。我有一个基于类别的待办事项集合。它有 x 行数。内置了将这些待办事项分配给所有者的功能。我想显示每个类别的作业进度。我怎样才能让这个查询正确。感谢帮助

类别 = [{ id: DB, Title: Database, Desc: Database Fixes, }, { id: NET, Title: Network, Desc: Network Fixes, }, ...]

县=

[{
id: AL
category_id: DB,
Title: Alabama,
},
{
id: AK
category_id: DB,
Title: Alaska
},
{
id: AZ
category_id: DB,
Title: Arizona
},
...]

待办事项=

id: TD1
County_id: AL,
Title: Installation,
assigned: 1,
user: ASED
},
{
id: TD2
County_id: AL,
Title: Documentation,
assigned: 0,
user: ""
},
{
id: TD3
County_id: AL,
Title: Migration,
assigned: 1,
user: ILKQ
},
{
id: TD4
County_id: AK,
Title: Documentation,
assigned: 0,
user: ""
},
{
id: TD5
County_id: AZ,
Title: Testing,
assigned: 0,
user: ""
},
{
id: TD6
County_id: AZ,
Title: Documentation,
assigned: 1,
user: JUSJ
}]

预期结果=

[ {
    category_id: DB,
    Title: Database,
    Desc: Database Fixes,
    total_rec: 4,
    total_assigned: 2
    },
    {
    category_id: NET,
    Title: Network,
    Desc: Network Fixes,
    total_rec: 2,
    total_assigned:1
    }]

Answer 1

我猜你想要这样的东西：

    db.Category.aggregate([
  {
    "$lookup": {
      "from": "county",
      "localField": "id",
      "foreignField": "category_id",
      "as": "county"
    }
  },
  {
    $project: {
      Desc: 1,
      county: "$county.id",
      Title: 1,
      id: 1
    }
  },
  {
    "$lookup": {
      "from": "ToDo",
      "localField": "county",
      "foreignField": "County_id",
      "as": "tasks"
    }
  },
  {
    "$project": {
      "total_assigned": {
        "$sum": {
          "$sum": "$tasks.assigned"
        }
      },
      "Desc": 1,
      total_rec: {
        $size: "$tasks"
      },
      category_id: "$id",
      Title: 1,
      _id: 0
    }
  },
])

从类别开始，使用 $lookup 获取所有国家，然后使用另一个获取所有 ToDos。你可以在操场上看到它是如何工作的here。

顺便说一句，请注意我需要在您的示例中更改亚利桑那州的 category_id 以匹配您想要的结果...

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