How do I search according to fields in inner classes using MongoDB db.coll.find()?

Use dot notation(.) to search in inner classes using MongoDB. Let us first create a collection with documents −

> db.searchInInnerDemo.insertOne(
...    {
...       "StudentFirstName" : "Robert",
...       "StudentTechnicalDetails":
...       {
...          "StudentBackEndTechnology" : "MongoDB",
...          "StudentLanguage" : "Java"
...       }
...    }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cd2dd89b64f4b851c3a13d2")
}
>
> db.searchInInnerDemo.insertOne(
...    {
...       "StudentFirstName" : "David",
...       "StudentTechnicalDetails":
...       {
...          "StudentBackEndTechnology" : "MySQL",
...          "StudentLanguage" : "PHP"
...       }
...    }
... );
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cd2dda3b64f4b851c3a13d3")
}

Following is the query to display all documents from a collection with the help of find() method −

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

This will produce the following output −

{
   "_id" : ObjectId("5cd2dd89b64f4b851c3a13d2"),
   "StudentFirstName" : "Robert",
   "StudentTechnicalDetails" : {
      "StudentBackEndTechnology" : "MongoDB",
      "StudentLanguage" : "Java"
   }
}
{
   "_id" : ObjectId("5cd2dda3b64f4b851c3a13d3"),
   "StudentFirstName" : "David",
   "StudentTechnicalDetails" : {
      "StudentBackEndTechnology" : "MySQL",
      "StudentLanguage" : "PHP"
   }
}

Case 1 − Query to search in inner class to match only one property −

>db.searchInInnerDemo.find({"StudentTechnicalDetails.StudentBackEndTechnology":"MongoDB"}).pretty();

This will produce the following output −

{
   "_id" : ObjectId("5cd2dd89b64f4b851c3a13d2"),
   "StudentFirstName" : "Robert",
   "StudentTechnicalDetails" : {
      "StudentBackEndTechnology" : "MongoDB",
      "StudentLanguage" : "Java"
   }
}

Case 2 − Query to search the document with scanning full field name −

>db.searchInInnerDemo.find({"StudentTechnicalDetails":{"StudentBackEndTechnology":"MongoDB","StudentLanguage":"Java"}}).pretty();

This will produce the following output −

{
   "_id" : ObjectId("5cd2dd89b64f4b851c3a13d2"),
   "StudentFirstName" : "Robert",
   "StudentTechnicalDetails" : {
      "StudentBackEndTechnology" : "MongoDB",
      "StudentLanguage" : "Java"
   }
}