Dalia-assignment-w4

Week4/homework/ db.js

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+
+const { MongoClient } = require("mongodb");
+
+async function connectDB() {
+  const client = new MongoClient("mongodb://localhost:27017");
+  await client.connect();
+  const db = client.db("databaseWeek4");
+  return { db, client };
+}
+
+module.exports = connectDB;

Week4/homework/ index.js

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+
+
+const connectDB = require("./db");
+
+const {
+  getPopulationByCountryPerYear,
+  getContinentPopulationByYearAndAge
+} = require("./ex1-aggregation/queries");
+
+const setup = require("./ex2-transactions/setup");
+const transfer = require("./ex2-transactions/transfer");
+
+async function main() {
+  console.log("Running Setup...");
+  await setup();
+
+  console.log("\nRunning Transfer Transaction...");
+  await transfer(101, 102, 1000, "Test transfer");
+
+  console.log("\n=== Accounts After Transfer ===");
+  const { db, client } = await connectDB();
+  const accounts = await db.collection("accounts").find().toArray();
+  console.log(accounts);
+  await client.close();
+
+  console.log("\nRunning Aggregation Queries...");
+  const { db: db2, client: client2 } = await connectDB();
+
+  const agg1 = await getPopulationByCountryPerYear(db2, "Netherlands");
+  console.log("\nPopulation by Year for Netherlands:");
+  console.log(agg1);
+
+  const agg2 = await getContinentPopulationByYearAndAge(db2, 2020, "100+");
+  console.log("\nContinents Data for age 100+ in 2020:");
+  console.log(agg2);
+
+  await client2.close();
+}
+
+main();

Week4/homework/ex1-aggregation/queries.js

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+
+async function getPopulationByCountryPerYear(db, countryName) {
+  return await db.collection("population").aggregate([
+    { $match: { Country: countryName } },
+    {
+      $group: {
+        _id: "$Year",
+        countPopulation: { $sum: { $add: ["$M", "$F"] } }
+      }
+    },
+    { $sort: { _id: 1 } }
+  ]).toArray();
+}
+
+async function getContinentPopulationByYearAndAge(db, year, age) {
+  return await db.collection("population").aggregate([
+    { $match: { Year: year, Age: age } },
+    {
+      $addFields: {
+        TotalPopulation: { $add: ["$M", "$F"] }
+      }
+    }
+  ]).toArray();
+}
+
+module.exports = {
+  getPopulationByCountryPerYear,
+  getContinentPopulationByYearAndAge
+};

Week4/homework/ex2-transactions/setup.js

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+
+const connectDB = require("../db");
+
+async function setup() {
+  const { db, client } = await connectDB();
+  const accounts = db.collection("accounts");
+
+  await accounts.deleteMany({});
+
+  await accounts.insertMany([
+    {
+      account_number: 101,
+      balance: 5000,
+      account_changes: []
+    },
+    {
+      account_number: 102,
+      balance: 2000,
+      account_changes: []
+    },
+    {
+      account_number: 103,
+      balance: 8000,
+      account_changes: []
+    }
+  ]);
+
+  console.log("Setup done: accounts created.");
+  await client.close();
+}
+
+module.exports = setup;

Week4/homework/ex2-transactions/transfer.js

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+
+const connectDB = require("../db");
+
+async function transfer(fromAcc, toAcc, amount, remark) {
+  const { db, client } = await connectDB();
+  const accounts = db.collection("accounts");
+
+  const session = client.startSession();
+
+  try {
+    await session.withTransaction(async () => {
+      const from = await accounts.findOne({ account_number: fromAcc }, { session });
+      const to = await accounts.findOne({ account_number: toAcc }, { session });
+
+      if (!from || !to) throw new Error("Account not found.");
+      if (from.balance < amount) throw new Error("Insufficient funds.");
+
+      const nextChangeFrom =
+        (from.account_changes.at(-1)?.change_number || 0) + 1;
+
+      const nextChangeTo =
+        (to.account_changes.at(-1)?.change_number || 0) + 1;
+
+      await accounts.updateOne(
+        { account_number: fromAcc },
+        {
+          $inc: { balance: -amount },
+          $push: {
+            account_changes: {
+              change_number: nextChangeFrom,
+              amount: -amount,
+              changed_date: new Date(),
+              remark
+            }
+          }
+        },
+        { session }
+      );
+
+      await accounts.updateOne(
+        { account_number: toAcc },
+        {
+          $inc: { balance: amount },
+          $push: {
+            account_changes: {
+              change_number: nextChangeTo,
+              amount: amount,
+              changed_date: new Date(),
+              remark
+            }
+          }
+        },
+        { session }
+      );
+    });
+
+    console.log(`Transfer of ${amount} from ${fromAcc} to ${toAcc} completed.`);
+  } catch (err) {
+    console.log("Transaction failed:", err.message);
+  } finally {
+    await session.endSession();
+    await client.close();
+  }
+}
+
+module.exports = transfer;