Vlad-week4-DB

Week4/homework/ex1-aggregation/index.js

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+require("dotenv").config();
+const { MongoClient, ServerApiVersion } = require("mongodb");
+
+const DB = "databaseWeek4";
+const COLL = "populations";
+
+async function totalPopulationPerYear(client, country) {
+  const col = client.db(DB).collection(COLL);
+  const pipeline = [
+    { $match: { Country: country } },
+    {
+      $addFields: {
+        Year: { $toInt: "$Year" },
+        M: { $toLong: "$M" },
+        F: { $toLong: "$F" },
+      },
+    },
+    {
+      $group: {
+        _id: "$Year",
+        countPopulation: { $sum: { $add: ["$M", "$F"] } },
+      },
+    },
+    { $sort: { _id: 1 } },
+  ];
+  return col.aggregate(pipeline).toArray();
+}
+
+async function continentsForYearAge(client, year, age) {
+  const col = client.db(DB).collection(COLL);
+  const continents = [
+    "AFRICA",
+    "ASIA",
+    "EUROPE",
+    "LATIN AMERICA AND THE CARIBBEAN",
+    "NORTHERN AMERICA",
+    "OCEANIA",
+  ];
+  const pipeline = [
+    {
+      $match: {
+        Country: { $in: continents },
+        Year: { $in: [year, String(year)] },
+        Age: age,
+      },
+    },
+    {
+      $addFields: {
+        Year: { $toInt: "$Year" },
+        M: { $toLong: "$M" },
+        F: { $toLong: "$F" },
+        TotalPopulation: { $add: [{ $toLong: "$M" }, { $toLong: "$F" }] },
+      },
+    },
+    // { $sort: { Country: 1 } } // optional
+  ];
+  return col.aggregate(pipeline).toArray();
+}
+
+async function main() {
+  const client = new MongoClient(process.env.MONGODB_URL, {
+    serverApi: ServerApiVersion.v1,
+  });
+  await client.connect();
+  try {
+    const nl = await totalPopulationPerYear(client, "Netherlands");
+    console.log(nl);
+
+    const y2020 = await continentsForYearAge(client, 2020, "100+");
+    console.log(y2020);
+  } finally {
+    await client.close();
+  }
+}
+
+main().catch(console.error);

Week4/homework/ex2/index.js

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+// Week4/homework/ex2-transactions/index.js
+import "dotenv/config";
+import { MongoClient } from "mongodb";
+import { setup } from "./setup.js";
+import { transfer } from "./transfer.js";
+
+const DB = "databaseWeek4";
+const COLL = "accounts";
+
+async function showAccounts(label) {
+  const client = new MongoClient(process.env.MONGODB_URL);
+  await client.connect();
+  try {
+    const docs = await client
+      .db(DB)
+      .collection(COLL)
+      .find({}, { projection: { _id: 0 } })
+      .sort({ account_number: 1 })
+      .toArray();
+    console.log(`\n=== ${label} ===`);
+    console.table(
+      docs.map((d) => ({
+        account_number: d.account_number,
+        balance: d.balance,
+        last_change: d.account_changes?.[d.account_changes.length - 1],
+      }))
+    );
+  } finally {
+    await client.close();
+  }
+}
+
+async function main() {
+  await setup();
+
+  await showAccounts("Before transfer");
+
+  await transfer({
+    from: 101,
+    to: 102,
+    amount: 1000,
+    remark: "lesson W4 transfer",
+  });
+
+  await showAccounts("After transfer");
+}
+
+main().catch(console.error);

Week4/homework/ex2/setup.js

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+// Week4/homework/ex2-transactions/setup.js
+import "dotenv/config";
+import { MongoClient } from "mongodb";
+
+const DB = "databaseWeek4";
+const COLL = "accounts";
+
+export async function setup() {
+  const client = new MongoClient(process.env.MONGODB_URL);
+  await client.connect();
+  try {
+    const db = client.db(DB);
+    const col = db.collection(COLL);
+
+    await col.drop().catch(() => {});
+    await db.createCollection(COLL);
+
+    await col.createIndex({ account_number: 1 }, { unique: true });
+
+    const now = new Date();
+    await col.insertMany([
+      {
+        account_number: 101,
+        balance: 5000,
+        account_changes: [
+          {
+            change_number: 1,
+            amount: 5000,
+            changed_date: now,
+            remark: "initial deposit",
+          },
+        ],
+      },
+      {
+        account_number: 102,
+        balance: 1000,
+        account_changes: [
+          {
+            change_number: 1,
+            amount: 1000,
+            changed_date: now,
+            remark: "initial deposit",
+          },
+        ],
+      },
+    ]);
+
+    console.log("setup: accounts seeded");
+  } finally {
+    await client.close();
+  }
+}
+
+if (import.meta.url === `file://${process.argv[1]}`) {
+  setup().catch(console.error);
+}

Week4/homework/ex2/transfer.js

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+// Week4/homework/ex2-transactions/transfer.js
+import { MongoClient, ServerApiVersion } from "mongodb";
+import "dotenv/config";
+
+const DB = "databaseWeek4";
+const COLL = "accounts";
+
+export async function transfer({ from, to, amount, remark }) {
+  if (!Number.isFinite(amount) || amount <= 0) {
+    throw new Error("Amount must be a positive number");
+  }
+  if (from === to) {
+    throw new Error("From and To accounts must be different");
+  }
+
+  const client = new MongoClient(process.env.MONGODB_URL, {
+    serverApi: ServerApiVersion.v1,
+  });
+  await client.connect();
+
+  const session = client.startSession();
+  try {
+    const col = client.db(DB).collection(COLL);
+
+    const [a, b] = from < to ? [from, to] : [to, from];
+
+    const result = await session.withTransaction(
+      async () => {
+        const [accA, accB] = await Promise.all([
+          col.findOne({ account_number: a }, { session }),
+          col.findOne({ account_number: b }, { session }),
+        ]);
+        if (!accA || !accB) throw new Error("Account not found");
+
+        const accFrom = accA.account_number === from ? accA : accB;
+        const accTo = accA.account_number === to ? accA : accB;
+
+        if (accFrom.balance < amount) {
+          throw new Error("Insufficient funds");
+        }
+
+        const nextChangeFrom =
+          (accFrom.account_changes?.[accFrom.account_changes.length - 1]
+            ?.change_number ?? 0) + 1;
+        const nextChangeTo =
+          (accTo.account_changes?.[accTo.account_changes.length - 1]
+            ?.change_number ?? 0) + 1;
+
+        const now = new Date();
+
+        const updFrom = await col.updateOne(
+          { _id: accFrom._id },
+          {
+            $inc: { balance: -amount },
+            $push: {
+              account_changes: {
+                change_number: nextChangeFrom,
+                amount: -amount,
+                changed_date: now,
+                remark,
+              },
+            },
+          },
+          { session }
+        );
+        if (updFrom.modifiedCount !== 1) {
+          throw new Error("Debit update failed");
+        }
+
+        const updTo = await col.updateOne(
+          { _id: accTo._id },
+          {
+            $inc: { balance: amount },
+            $push: {
+              account_changes: {
+                change_number: nextChangeTo,
+                amount,
+                changed_date: now,
+                remark,
+              },
+            },
+          },
+          { session }
+        );
+        if (updTo.modifiedCount !== 1) {
+          throw new Error("Credit update failed");
+        }
+      },
+      {
+        readConcern: { level: "snapshot" },
+        writeConcern: { w: "majority" },
+        readPreference: "primary",
+      }
+    );
+
+    if (result) {
+      console.log(
+        `transfer: success (from ${from} to ${to}, amount ${amount})`
+      );
+    } else {
+      throw new Error("Transaction aborted by driver");
+    }
+  } finally {
+    await session.endSession();
+    await client.close();
+  }
+}