Syntax error Retrieve only the queried element in an object array in MongoDB collection?

Retrieve only the queried element in an object array in MongoDB collection?

You can use projection operator $elemMatch to filter in queried element in an object array in MongoDB collection. To retrieve only the queried element in an object array in MongoDB, let us first create a collection with documents object array.

The query is as follows:

> db.objectArray.insert({"Persons":[
   {"PersonName":"Adam","PersonSalary":25000},{"PersonName":"Larry","PersonSalary":27000
   }]});
   WriteResult({ "nInserted" : 1 })
> db.objectArray.insert({"Persons":[
   {"PersonName":"David","PersonSalary":32000},{"PersonName":"Carol","PersonSalary":77000
   }]});
   WriteResult({ "nInserted" : 1 })

Now you can display all the documents with the help of find(). The query is as follows:

> db.objectArray.find().pretty();

The following is the output:

{
   "_id" : ObjectId("5c6bfadc68174aae23f5ef53"),
   "Persons" : [
      {
         "PersonName" : "Adam",
         "PersonSalary" : 25000
      },
      {
         "PersonName" : "Larry",
         "PersonSalary" : 27000
      }
   ]
}
{
   "_id" : ObjectId("5c6bfb0968174aae23f5ef54"),
   "Persons" : [
      {
         "PersonName" : "David",
         "PersonSalary" : 32000
      },
      {
         "PersonName" : "Carol",
         "PersonSalary" : 77000
      }
   ]
}

Here is the query to retrieve only the queried element in an object array in MongoDB. Here In _id:0 is added to exclude the id property(do not show the _id property):

> db.objectArray.find({"Persons.PersonSalary":25000}, {
_id:0,Persons:{$elemMatch:{"PersonSalary":25000}}}).pretty();

The following is the output:

{
   "Persons" : [
      {
         "PersonName" : "Adam",
         "PersonSalary" : 25000
      }
   ]
}

Alternate way to do the above task is with the help of projection operator $. The query is as follows:

> db.objectArray.find({"Persons.PersonSalary":25000}, { _id:0,'Persons.$':1}).pretty();

The following is the output:

{
   "Persons" : [
      {
         "PersonName" : "Adam",
         "PersonSalary" : 25000
      }
   ]
}
Updated on: 2019-07-30T22:30:25+05:30

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