Querying internal array size in MongoDB

by

if username Alex is unique, you can use next code:

db.test.insert({username:"Alex", tags: ['C#', 'Java', 'C++'] });
db.test.aggregate(
  {$match: {username : "Alex"}}, 
  {$unwind: "$tags"},
  {$project: {count:{$add:1}}},
  {$group: {_id: null, number: {$sum: "$count" }}}
);
{ "result" : [ { "_id" : null, "number" : 3 } ], "ok" : 1 }

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