How to show specific object from array of object in MongoDB

Question

My document structure is as follow :

{
    "_id" : ObjectId("621e438004f5eb0b16ce6e34"),
    "h_name" : "WWW Hospital",
    "specializations" : [
        "Gynaec",
        "Orthopaedic"
    ],
    "doctors" : [
        {
            "dr_name" : "Dr. Mehta",
            "visit_day" : "Monday"
        },
        {
            "dr_name" : "Dr. Kale",
            "visit_day" : "Monday"
        },
        {
            "dr_name" : "Dr. MK",
            "visit_day" : "Tuesday"
        }
    ],
    "public_review" : [
        {
            "p_name" : "Ajit",
            "rating" : 4
        },
        {
            "p_name" : "Vijay",
            "rating" : 2
        },
        {
            "p_name" : "Piyush",
            "rating" : 4
        }
    ]
}

How to perform the following query

List the names of doctors who are visiting “Jehangir Hospital ” on
Mondays

I try this :

db.hospital.find({
  h_name: 'WWW Hospital',
  doctors: {
    $elemMatch: {
      visit_day: 'Monday'
    }
  }
}, {
  _id: 0,
  "doctors.dr_name": 1,
  "doctors.visit_day": 1
})

Output :

{ "doctors" : [ { "dr_name" : "Dr. Mehta", "visit_day" : "Monday" }, { "dr_name" : "Dr. Kale", "visit_day" : "Monday" }, { "dr_name" : "Dr. MK", "visit_day" : "Tuesday" } ] }

The output contains an object of Dr. MK also whose visit_day is Tuesday I want to list dr_names whose visit_day is Monday

Dharmaraj · Accepted Answer · 2022-03-01 18:01:59Z

1

The $elemMatch should be in projection object as shown below:

db.collection.find({
  h_name: "WWW Hospital",
  "doctors.visit_day": "Monday"
}, {
  doctors: {
    $elemMatch: {
      visit_day: "Monday"
    }
  }
})

However $elemMatch returns first matching element only. Try using $filter instead:

db.collection.find({
  h_name: "WWW Hospital"
},
{
  doctors: {
    $filter: {
      input: "$doctors",
      as: "doctor",
      cond: {
        $eq: [
          "$$doctor.visit_day",
          "Monday"
        ]
      }
    }
  }
})

answered Mar 1, 2022 at 18:01

Dharmaraj

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