Yaroslav kazeev w4 databases

Week4/homework/ex1-aggregation/index.js

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+import { MongoClient } from "mongodb";
+import "dotenv/config";
+const clientMongo = new MongoClient(process.env.MONGODB_URL);
+import fs from "fs";
+import csv from "csv-parser";
+let data;
+
+async function processCSV(fileName) {
+  return new Promise((resolve, reject) => {
+    const data = [];
+    fs.createReadStream(fileName)
+      .pipe(csv())
+      .on("data", (row) => data.push(row))
+      .on("end", () => resolve(data))
+      .on("error", (err) => reject(err));
+  });
+}
+
+async function getTotalPopulationByYear(collection, country) {
+  const result = await collection
+    .aggregate([
+      { $match: { Country: country } },
+      {
+        $group: {
+          _id: { $toInt: "$Year" },
+          countPopulation: {
+            $sum: {
+              $add: [{ $toInt: "$M" }, { $toInt: "$F" }],
+            },
+          },
+        },
+      },
+      { $sort: { _id: 1 } },
+    ])
+    .toArray();
+  return result;
+}
+
+async function getContinentsPopulation(collection, year, age) {
+  const result = await collection
+    .aggregate([
+      {
+        $match: {
+          Year: year.toString(),
+          Age: age.toString(),
+          // Filter only continents by checking if Country is uppercase
+          $expr: {
+            $eq: ["$Country", { $toUpper: "$Country" }],
+          },
+        },
+      },
+      {
+        $addFields: {
+          TotalPopulation: { $add: [{ $toInt: "$M" }, { $toInt: "$F" }] },
+        },
+      },
+      {
+        $project: {
+          _id: 1,
+          Country: 1,
+          Year: 1,
+          Age: 1,
+          M: 1,
+          F: 1,
+          TotalPopulation: 1,
+        },
+      },
+    ])
+    .toArray();
+  return result;
+}
+
+async function main() {
+  try {
+    await clientMongo.connect();
+    const db = clientMongo.db("databaseWeek4");
+    const collection = db.collection("population_pyramid");
+    data = await processCSV(
+      "./Week4/homework/ex1-aggregation/population_pyramid_1950-2022.csv"
+    );
+    await collection.insertMany(data);
+    data = await getTotalPopulationByYear(collection, "Netherlands");
+    console.log(
+      "\nPopulation by Year (Netherlands):\n",
+      JSON.stringify(data, null, 2)
+    );
+    data = await getContinentsPopulation(collection, "2020", "100+");
+    console.log(
+      "\nPopulation by Continent (2020, 100+):\n",
+      JSON.stringify(data, null, 2)
+    );
+  } catch (error) {
+    console.error("Error connecting to MongoDB:", error);
+  } finally {
+    await clientMongo.close();
+    console.log("Connection to MongoDB closed");
+  }
+}
+
+main();

Week4/homework/ex2-transactions/data.json

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+{
+  "accounts": [
+    { "account_number": 101, "balance": 5000 },
+    { "account_number": 102, "balance": 12000 },
+    { "account_number": 103, "balance": 7500 },
+    { "account_number": 104, "balance": 3000 },
+    { "account_number": 105, "balance": 9500 }
+  ],
+  "account_changes": [
+    {
+      "account_number": 101,
+      "amount": 1000,
+      "changed_date": "2025-09-01",
+      "remark": "Salary deposit"
+    },
+    {
+      "account_number": 102,
+      "amount": -500,
+      "changed_date": "2025-09-02",
+      "remark": "Grocery shopping"
+    },
+    {
+      "account_number": 103,
+      "amount": 2000,
+      "changed_date": "2025-09-03",
+      "remark": "Freelance payment"
+    },
+    {
+      "account_number": 104,
+      "amount": -1000,
+      "changed_date": "2025-09-04",
+      "remark": "Rent payment"
+    },
+    {
+      "account_number": 105,
+      "amount": 1500,
+      "changed_date": "2025-09-05",
+      "remark": "Gift received"
+    }
+  ]
+}

Week4/homework/ex2-transactions/index.js

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+import { setup } from "./setup.js";
+import { transfer } from "./transfer.js";
+let clientMongo, account;
+async function main() {
+  try {
+    ({ clientMongo, account } = await setup());
+    const transactionDetails = {
+      donator_account_number: 101,
+      receiver_account_number: 102,
+      amount: 1000,
+      changed_date: new Date().toISOString().slice(0, 10), // 'YYYY-MM-DD'
+      remark: `Transfer from 101 to 102`,
+    };
+    await transfer(clientMongo, account, transactionDetails);
+  } catch (error) {
+    console.error("Error:", error);
+  } finally {
+    await clientMongo.close();
+    console.log("Connection to MongoDB closed");
+  }
+}
+
+main();

Week4/homework/ex2-transactions/setup.js

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+import { MongoClient } from "mongodb";
+import "dotenv/config";
+import fs from "fs";
+
+export async function setup() {
+  const { accounts, account_changes } = JSON.parse(
+    fs.readFileSync("./Week4/homework/ex2-transactions/data.json")
+  );
+  const clientMongo = new MongoClient(process.env.MONGODB_URL);
+  await clientMongo.connect();
+  const db = clientMongo.db("databaseWeek4");
+  const account = await db.createCollection("accounts");
+  await account.deleteMany({});
+  for (const acc of accounts) {
+    acc.account_changes = account_changes
+      .filter((a) => a.account_number === acc.account_number)
+      .map((a) => {
+        delete a.account_number;
+        return a;
+      });
+    await account.insertOne(acc);
+  }
+  return { clientMongo, account };
+}

Week4/homework/ex2-transactions/transaction.js

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+import { Client } from "pg";
+const config = {
+  host: "localhost",
+  user: "hyfuser",
+  password: "hyfpassword",
+  database: "transactions_week3",
+  port: 5432,
+};
+const client = new Client(config);
+
+async function seedDatabase(client) {
+  try {
+    await client.connect();
+    console.log("Connected to PostgreSQL database!");
+
+    const donator_account_number = 101;
+    const receiver_account_number = 102;
+    const amount = 1000;
+    const changed_date = new Date().toISOString().slice(0, 10); // 'YYYY-MM-DD'
+    const remark = `Transfer from 101 to 102`;
+
+    await client.query("BEGIN");
+    await client.query(
+      "UPDATE ACCOUNT SET balance = balance - $1 WHERE account_number = $2",
+      [amount, donator_account_number]
+    );
+    await client.query(
+      "UPDATE ACCOUNT SET balance = balance + $1 WHERE account_number = $2",
+      [amount, receiver_account_number]
+    );
+    await client.query(
+      "INSERT INTO account_changes(account_number, amount, changed_date, remark) VALUES($1, $2, $3, $4)",
+      [donator_account_number, -amount, changed_date, remark]
+    );
+    await client.query(
+      "INSERT INTO account_changes(account_number, amount, changed_date, remark) VALUES($1, $2, $3, $4)",
+      [receiver_account_number, amount, changed_date, remark]
+    );
+    await client.query("COMMIT");
+    console.log("Transaction completed!");
+  } catch (error) {
+    console.error("Error seeding database:", error);
+  } finally {
+    await client.end();
+  }
+}
+
+seedDatabase(client);

Week4/homework/ex2-transactions/transfer.js

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+export async function transfer(clientMongo, account, transactionDetails) {
+  const {
+    donator_account_number,
+    receiver_account_number,
+    amount,
+    changed_date,
+    remark,
+  } = transactionDetails;
+  const session = clientMongo.startSession();
+  const transactionOptions = {
+    readPreference: "primary",
+    readConcern: { level: "local" },
+    writeConcern: { w: "majority" },
+  };
+  try {
+    await session.withTransaction(async () => {
+      await account.updateOne(
+        { account_number: donator_account_number },
+        {
+          $inc: { balance: -amount },
+          $push: { account_changes: { amount: -amount, changed_date, remark } },
+        },
+        { session }
+      );
+      await account.updateOne(
+        { account_number: receiver_account_number },
+        {
+          $inc: { balance: amount },
+          $push: { account_changes: { amount: amount, changed_date, remark } },
+        },
+        { session }
+      );
+    }, transactionOptions);
+    console.log("Transaction committed.");
+  } catch (error) {
+    console.log("Transaction aborted.", error);
+    throw new Error(error);
+  } finally {
+    await session.endSession();
+    console.log("Transaction completed!");
+  }
+}