aggregation.js

db.statistic.aggregate(

	// Pipeline
	[
		// Stage 1
		{
			$group: {
				_id: '$user._id',
				total: { $sum: 1 }
			}
		},

		// Stage 2
		{
			$sort: {
				total: -1
			}
		},

		// Stage 3
		{
			$limit: 100
		},

		// Stage 4
		{
			$lookup: {
			    "from" : "users",
			    "localField" : "_id",
			    "foreignField" : "_id",
			    "as" : "user"
			}
		},

		// Stage 5
		{
			$unwind: {
			  path: '$user'
			}
		},

		// Stage 6
		{
			$project: {
				total: 1,
				'user.username': 1,
				'user.email': 1,
				'user.firstName': 1,
				'user.lastName': 1,
				'user.provider': 1
			}
		},

	]

);