Aggregation in MongoDB for nested documents?

For aggregation in MongoDB, use aggregate(). Let us create a collection with documents −

> db.demo199.insertOne( ...   { ...      "details1":{ ...         "details2":{ ...            "details3":{ ...               "Name":"Chris", ...               "details4":{ ...                  "details5":{ ...                     "v1":10, ...                     "v2":20, ...                     "v3":30 ...                  } ...               } ...    }}}} ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3c24aa03d395bdc21346e2") } > > db.demo199.insertOne( ...   { ...      "details1":{ ...         "details2":{ ...            "details3":{ ...               "Name":"Chris", ...               "details4":{ ...                  "details5":{ ...                     "v1":30, ...                     "v2":40, ...                     "v3":50 ...                  } ...               } ...   }}}} ...); {    "acknowledged" : true,    "insertedId" : ObjectId("5e3c24ab03d395bdc21346e3") }

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

> db.demo199.find();

This will produce the following output −

{ "_id" : ObjectId("5e3c24aa03d395bdc21346e2"), "details1" : { "details2" : { "details3" : { "Name" : "Chris", "details4" : { "details5" : { "v1" : 10, "v2" : 20, "v3" : 30 } } } } } } { "_id" : ObjectId("5e3c24ab03d395bdc21346e3"), "details1" : { "details2" : { "details3" : { "Name" : "Chris", "details4" : { "details5" : { "v1" : 30, "v2" : 40, "v3" : 50 } } } } } }

Following is the query for aggregation in MongoDB for nested documents −

> var out = [ ...   { ...      "$unwind": "$details1.details2" ...   }, ...   { ...      "$group": { ...         "_id": "$details1.details2._id", ...         "v1": { "$sum": "$details1.details2.details3.details4.details5.v1" }, ...         "v2": { "$sum": "$details1.details2.details3.details4.details5.v2" }, ...         "v3": { "$sum": "$details1.details2.details3.details4.details5.v3" }, ...      } ...   } ...] > result = db.demo199.aggregate(out);

This will produce the following output −

{ "_id" : null, "v1" : 40, "v2" : 60, "v3" : 80 }