Count posts of user with default value-CodePudding

Supposed I have a data of

[
    {
        "_id": "629eb5ced774223d36a68907",
        "userId": "629eb22698df1015e980a98f",
        "posts": [
            {
                "_id": "629eb59ad774223d36a688fa",
                "title": "titletestz",
                "body": "bodyz",
                "createdAt": "2022-06-07T02:19:06.314Z",
                "updatedAt": "2022-06-07T02:19:06.314Z",
                "__v": 0
            },
            {
                "_id": "629eb59ad774223d36a688fc",
                "title": "titletestx",
                "body": "bodyx",
                "createdAt": "2022-06-07T02:19:06.879Z",
                "updatedAt": "2022-06-07T02:19:06.879Z",
                "__v": 0
            }
        ],
        "createdAt": "2022-06-07T02:19:58.206Z",
        "updatedAt": "2022-06-07T02:19:58.206Z",
        "__v": 0
    },
    {
        "_id": "629ebf8b775b5cd326b1c41c",
        "userId": "629eb22698df1015e980a98f",
        "posts": [
            {
                "_id": "629eb22c98df1015e980a995",
                "title": "ttle3",
                "body": "ttile3",
                "createdAt": "2022-06-07T02:04:28.787Z",
                "updatedAt": "2022-06-07T02:04:28.787Z",
                "__v": 0
            }
        ],
        "createdAt": "2022-06-07T03:01:31.065Z",
        "updatedAt": "2022-06-07T03:01:31.065Z",
        "__v": 0
    }
]

I want to count the posts of a specific user

let start = new Date()
start = start.setHours(0,0,0,0)

let end = new Date()
end = start.setHours(23,59,59,999)

model.aggregate([
  {
    $match: {
      userId,
      createdAt: {
        $gte: start,
        $lt: end
      }
    }
  },
  {
    $unwind : '$posts',
  },
  {
    $count: 'count'
  }
])

now it does work

[
  {
    "total": 3
  }
]

however, I want to set a default value of 0 of user if it doesn't contain any posts, like this:

[
  {
    "total": 0
  }
]

right now I just having a response of an empty array [] if user doesn't have any posts.

any idea how can I achieve this using aggregate in monggo?

CodePudding user response：

It Will return empty array on no matches.

let start = new Date()
start = start.setHours(0,0,0,0)

let end = new Date()
end = start.setHours(23,59,59,999);

db.collection.aggregate(
  [
    {
      $match: {
      userId,
      createdAt: {
        $gte: start,
        $lt: end
      }
    }
    },
    {
      $group: {
         '$posts'
      }
    },
    {
      $count: "totalCount"
    }
  ]
)

CodePudding user response：

using $facet and $ifNull

mongo playground

db.collection.aggregate([
  {
    "$facet": {
      count: [
        {
          $match: {
            userId,
            createdAt: {
              $gte: start,
              $lt: end
            }
          }
        },
        {
          "$addFields": {
            total: {
              "$ifNull": [
                1,
                0,
                
              ]
            }
          }
        },
        {
          $unwind: "$posts"
        },
        {
          "$count": "total"
        },
        
      ]
    }
  },
  {
    "$project": {
      "total": {
        "$ifNull": [
          { "$arrayElemAt": ["$count.total", 0] },
          0
        ]
      }
    }
  }
])