CODEWITHSUNDEEP
node.jsmongodbaggregation-framework
Pallab
Pallab

Reputation: 175

MongoDB aggregation and lookup

I  made the below query:  

db.employees.aggregate([
  {
    $match: {
      isActive: true,
      
    }
  },
  {
    $lookup: {
      from: "shifts",
      localField: "_id",
      foreignField: "employee",
      as: "shifts"
    }
  },
  {
    $unwind: {
      path: "$shifts",
      preserveNullAndEmptyArrays: true,
      
    }
  }
])

And now getting the below result:

[
    {
        "_id": "621eedae92979fd8f0e9451d",
        "name": "Pallab Koley",
        "shifts": {
            "_id": "62636b9fcbda6d2b17f5cae0",
            "month": "2022-05",
            "shift": [
                {
                    "date": "2022-05-01",
                    "shiftId": "622bb0f4b88dc92e3c2cac56"
                }
            ]
        }
    },
    {
        "_id": "621eedae92979fd8f0e9451d",
        "name": "Pallab Koley",
        "shifts": {
            "_id": "62636bb3cbda6d2b17f5cae2",
            "month": "2022-04",
            "shift": [
                {
                    "date": "2022-04-01",
                    "shiftId": "622bb0f4b88dc92e3c2cac56"
                }
            ]
        }
    },
    {
        "_id": "62626a7446ba9a911a623b37",
        "name": "Pinki Das",
        "shifts": {
            "_id": "62636ba4cbda6d2b17f5cae1",
            "month": "2022-05",
            "shift": [
                {
                    "date": "2022-05-01",
                    "shiftId": "622bb0f4b88dc92e3c2cac56"
                }
            ]
        }
    }
]

I need to filter the data with the particular month I am adding

{
    $unwind: {
        path: '$shifts',
        preserveNullAndEmptyArrays: true,
    }
},
{
    $match: {
        "shifts.month": “2022-04”
    }
},

I am getting the result:

[
    {
        "_id": "621eedae92979fd8f0e9451d",
        "name": "Pallab Koley",
        "shifts": {
            "_id": "62636bb3cbda6d2b17f5cae2",
            "month": "2022-04",
            "shift": [
                {
                    "date": "2022-04-01",
                    "shiftId": "622bb0f4b88dc92e3c2cac56"
                }
            ]
        }
    }
]

But my requirement is that I need all other existing employees from the employees collection even also there is no record in shifts collection. Please help to get that.


Upvotes: 0

Views: 1018

Answers (1)

Yong Shun
Yong Shun

Reputation: 51160

Probably this is what you need.

  1. $match stage
  2. $lookup stage
  3. Remove $unwind stage.
  4. $project stage - With $filter operator to filter the document in shifts array which month is 2022-04.
db.collection.aggregate([
  // $match ,
  // $lookup,
  // Remove $unwind
  {
    $project: {
      id: 1,
      name: 1,
      shifts: {
        "$filter": {
          "input": "$shifts",
          "cond": {
            $eq: [
              "$$this.month",
              "2022-04"
            ]
          }
        }
      }
    }
  }
])

Sample Mongo Playground

Upvotes: 1

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