C100DEV Aggregation Framework — All Questions With Answers

db.sales.aggregate([
  { $group: { _id: "$category", total: { $sum: "$amount" } } },
  { $sort: { total: -1 } }
])

{
  "_id": 1, 
  "tags": ["red", "blue", "green"]
}

db.users.aggregate([
  { $project: { _id: 0, name: 1, age: 1 } },
  { $match: { age: { $gt: 25 } } }
])

db.sales.aggregate([
  { $match: { status: "A" } },
  { $lookup: { 
      from: "items", 
      localField: "item_id", 
      foreignField: "_id", 
      as: "details" 
  } },
  { $unwind: "$details" }
])

db.collection.aggregate([ { $group: { _id: "$category", total: { $sum: "$price" } } } ])

db.collection.aggregate([ { $project: { result: { $add: ["$price", "$tax"] } } } ])