Get the size of a collection in MongoDB using conditions?

Let us first create a collection with documents −

> dbmongoDBCollectionSizeDemoinsertOne({"Name":"John", "Age":23});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cf23e3db64a577be5a2bc16")
}
> dbmongoDBCollectionSizeDemoinsertOne({"Name":"Chris", "Age":24});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cf23e45b64a577be5a2bc17")
}
> dbmongoDBCollectionSizeDemoinsertOne({"Name":"Robert", "Age":26});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5cf23e4db64a577be5a2bc18")
}

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

> dbmongoDBCollectionSizeDemofind();

This will produce the following document −

{ "_id" : ObjectId("5cf23e3db64a577be5a2bc16"), "Name" : "John", "Age" : 23 }
{ "_id" : ObjectId("5cf23e45b64a577be5a2bc17"), "Name" : "Chris", "Age" : 24 }
{ "_id" : ObjectId("5cf23e4db64a577be5a2bc18"), "Name" : "Robert", "Age" : 26 }

Following is the query to get the collection size using conditions −

> var collectionsize = 0;
> dbmongoDBCollectionSizeDemofind({Name:'Robert'})forEach(function(d) {
   var s = Objectbsonsize(d);
   collectionsize=collectionsize +s;
})
> print(collectionsize);

This will produce the following document −

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