Need help to query nested array on mongo

Question

I am having following document structure in mongo db

{
"_id": {
    "name": "XYX",
    "rol_no": "1",
    "last_update_dt": "2021-05-10",
    
},
"stud_history": [{
    'std': 'xyz',
    'age': '16'
},
{
    'std': 'mnl',
    'age': '15'
}]
}

and i want to query data like

name:xyz, rol_no:1, last_update_dt: 2021-05-10 and age:16

here i have mentioned only 1 student but i need to query similarly for multiple students.

So my output will be

"_id": {
    "name": "XYX",
    "rol_no": "1",
    "last_update_dt": "2021-05-10",

},
'stud_history': {
    'std': 'xyz',
    'age': '16'
}

Please help

hhharsha36 · Accepted Answer · 2021-05-12 16:02:45Z

1

You have to use the $elemMatch operator inside the projection parameter of the match command to filter output that matches a certain condition.

db.collection.find({  // Find Query
  "_id.name": "XYX",
  "_id.rol_no": "1",
  "_id.last_update_dt": "2021-05-10",
},
{  // Projection Parameter
  "_id": 1,
  "stud_history": {
    "$elemMatch": {  // Filters array elements to those matching the provided condition
      "age": "16"
    }
  }
})

If you want to achieve the same using Aggregation, use the below query:

db.collection.aggregate([
  {
    "$match": {
      "_id.name": "XYX",
      "_id.rol_no": "1",
      "_id.last_update_dt": "2021-05-10",
      
    }
  },
  {
    "$project": {
      "_id": 1,
      "stud_history": {
        $filter: {
          input: "$stud_history",
          as: "item",
          cond: {
            $eq: [ "$$item.age", "16" ]
          }
        }
      }
    }
  },
  {
    // If you want the result to be an object instead of an array
    "$unwind": "$stud_history"
  },
])

edited May 12, 2021 at 16:02

answered May 12, 2021 at 11:32

hhharsha36

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2 Comments

Swapnil Patil Over a year ago

can you post with aggregation?

hhharsha36 Over a year ago

Add aggregation example to the answer

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