How to find a certain element in the MongoDB embedded document?

To find a certain element, use $project in MongoDB. Let us create a collection with documents −

> db.demo744.insertOne(
...    {
...       studentInformation:
...       [
...          {
...             studentName:"Robert",
...             grade:"A"
...          },
...          {
...             studentName:"Bob",
...             grade:"C"
...          },
...          {
...             studentName:"John",
...             grade:"B"
...          },
...          {
...             studentName:"Sam",
...             grade:"A"
...          }
...       ]
...    }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5ead928a57bb72a10bcf0684")
}

Display all documents from a collection with the help of find() method −

> db.demo744.find();

This will produce the following output −

{ "_id" : ObjectId("5ead928a57bb72a10bcf0684"), "studentInformation" : [ { "studentName" : "Robert", "grade" : "A" }, { "studentName" : "Bob", "grade" : "C" }, { "studentName" : "John", "grade" : "B" }, { "studentName" : "Sam", "grade" : "A" } ] }

Following is the query to find a certain element in the embedded document −

> db.demo744.aggregate(
...    { $unwind: '$studentInformation' },
...    { $match: {'studentInformation.grade':"A"}},
...    { $project: {"studentInformation.studentName": 1}}
... )

This will produce the following output −

{ "_id" : ObjectId("5ead928a57bb72a10bcf0684"), "studentInformation" : { "studentName" : "Robert" } }
{ "_id" : ObjectId("5ead928a57bb72a10bcf0684"), "studentInformation" : { "studentName" : "Sam" } }

AmitDiwan

Updated on: 30-Jun-2020

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