mongo.js

const pipeline_using_match_group = [
  // Stage 1: match the accounts with a balance greater than $1,000
  { $match: { balance: { $lt: 1000 } } },
  // Stage 2: Calculate average balance and total balance
  {
    $group: {
      _id: "$account_type",
      total_balance: { $sum: "$balance" },
      avg_balance: { $avg: "$balance" },
    },
  },
]

const pipeline_using_match_sort_project = [
  // Stage 1: $match - filter the documents (checking, balance >= 1500)
  { $match: { account_type: "checking", balance: { $gte: 1500 } } },

  // Stage 2: $sort - sorts the documents in descending order (balance)
  { $sort: { balance: -1 } },

  // Stage 3: $project - project only the requested fields and one computed field (account_type, account_id, balance, gbp_balance)
  {
    $project: {
      _id: 0,
      account_id: 1,
      account_type: 1,
      balance: 1,
      // GBP stands for Great British Pound
      gbp_balance: { $divide: ["$balance", 1.3] },
    },
  },
]

// A session allows you to perform multiple operations on MongoDB documents and collections 
// while ensuring data consistency and atomicity.
const session = db.getMongo().startSession()
session.startTransaction()
const account = session.getDatabase('< add database name here>').getCollection('<add collection name here>')
// Add database operations like .updateOne() here
session.commitTransaction() // or
session.abortTransaction()