diff --git a/Week2/prep/Database ER diagram (crow's foot).png b/Week2/prep/Database ER diagram (crow's foot).png
new file mode 100644
index 000000000..579c05848
Binary files /dev/null and b/Week2/prep/Database ER diagram (crow's foot).png differ
diff --git a/Week2/prep/Lucid connection.png b/Week2/prep/Lucid connection.png
new file mode 100644
index 000000000..8321abffd
Binary files /dev/null and b/Week2/prep/Lucid connection.png differ
diff --git a/Week2/prep/w1-prep-exe.sql b/Week2/prep/w1-prep-exe.sql
new file mode 100644
index 000000000..584bf10ec
--- /dev/null
+++ b/Week2/prep/w1-prep-exe.sql
@@ -0,0 +1,111 @@
+-- Очищаем существующие таблицы (для повторного запуска) -- Drop existing tables (for re-running the script)
+DROP TABLE IF EXISTS cuisines CASCADE;
+DROP TABLE IF EXISTS main_ingredients CASCADE;
+DROP TABLE IF EXISTS ingredients CASCADE;
+DROP TABLE IF EXISTS categories CASCADE;
+DROP TABLE IF EXISTS cooking_methods CASCADE;
+DROP TABLE IF EXISTS recipes CASCADE;
+DROP TABLE IF EXISTS recipe_categories CASCADE;
+DROP TABLE IF EXISTS recipe_ingredients CASCADE;
+DROP TABLE IF EXISTS recipe_methods CASCADE;
+DROP TABLE IF EXISTS recipe_ingredient_amounts CASCADE;
+
+
+
+---------------------------------------------------------
+-- 1. Таблица кухонь (Italian, Chinese, Japanese…) -- Table of Cuisines (Italian, Chinese, Japanese…)
+---------------------------------------------------------
+CREATE TABLE cuisines (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(100) NOT NULL UNIQUE
+);
+
+---------------------------------------------------------
+-- 2. Таблица основных ингредиентов (мясо, рыба, овощи) -- Table of Main Ingredients (meat, fish, vegetables)
+---------------------------------------------------------
+CREATE TABLE main_ingredients (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(150) NOT NULL UNIQUE
+);
+
+---------------------------------------------------------
+-- 3. Таблица всех возможных ингредиентов (морковь, масло, соль) -- Table of All Possible Ingredients (carrot, oil, salt)
+---------------------------------------------------------
+CREATE TABLE ingredients (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(150) NOT NULL UNIQUE
+);
+
+---------------------------------------------------------
+-- 4. Таблица категорий (суп, салат, десерт, завтрак) -- Table of Categories (soup, salad, dessert, breakfast)
+---------------------------------------------------------
+CREATE TABLE categories (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(100) NOT NULL UNIQUE
+);
+
+---------------------------------------------------------
+-- 5. Таблица методов приготовления (жарка, запекание, варка) -- Table of Cooking Methods (frying, baking, boiling)
+---------------------------------------------------------
+CREATE TABLE cooking_methods (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(100) NOT NULL UNIQUE
+);
+
+---------------------------------------------------------
+-- 6. Главная таблица рецептов -- Main Recipes Table
+---------------------------------------------------------
+CREATE TABLE recipes (
+    id SERIAL PRIMARY KEY,
+    name VARCHAR(255) NOT NULL,
+    cuisine_id INT,
+    main_ingredient_id INT,
+    FOREIGN KEY (cuisine_id) REFERENCES cuisines(id),
+    FOREIGN KEY (main_ingredient_id) REFERENCES main_ingredients(id)
+);
+
+---------------------------------------------------------
+-- 7. Связь рецепт ↔ категории (many-to-many) -- Recipe ↔ Categories Relationship (many-to-many)
+---------------------------------------------------------
+CREATE TABLE recipe_categories (
+    recipe_id INT NOT NULL,
+    category_id INT NOT NULL,
+    PRIMARY KEY (recipe_id, category_id),
+    FOREIGN KEY (recipe_id) REFERENCES recipes(id),
+    FOREIGN KEY (category_id) REFERENCES categories(id)
+);
+
+---------------------------------------------------------
+-- 8. Связь рецепт ↔ ингредиенты (many-to-many) -- Recipe ↔ Ingredients Relationship (many-to-many)
+---------------------------------------------------------
+CREATE TABLE recipe_ingredients (
+    recipe_id INT NOT NULL,
+    ingredient_id INT NOT NULL,
+    amount VARCHAR(50),  -- например "200 г", "1 ст.л."
+    PRIMARY KEY (recipe_id, ingredient_id),
+    FOREIGN KEY (recipe_id) REFERENCES recipes(id),
+    FOREIGN KEY (ingredient_id) REFERENCES ingredients(id)
+);
+
+---------------------------------------------------------
+-- 9. Связь рецепт ↔ методы приготовления (many-to-many) -- Recipe ↔ Cooking Methods Relationship (many-to-many)
+---------------------------------------------------------
+CREATE TABLE recipe_methods (
+    recipe_id INT NOT NULL,
+    method_id INT NOT NULL,
+    PRIMARY KEY (recipe_id, method_id),
+    FOREIGN KEY (recipe_id) REFERENCES recipes(id),
+    FOREIGN KEY (method_id) REFERENCES cooking_methods(id)
+);
+
+---------------------------------------------------------
+-- 10. кол-во ингредиентов в рецепте -- Quantity of Ingredients in Recipe
+---------------------------------------------------------
+CREATE TABLE recipe_ingredient_amounts (
+    recipe_id INT NOT NULL,
+    ingredient_id INT NOT NULL,
+    amount VARCHAR(50) NOT NULL,  -- например "200 г", "1 ст.л."
+    PRIMARY KEY (recipe_id, ingredient_id),
+    FOREIGN KEY (recipe_id) REFERENCES recipes(id),
+    FOREIGN KEY (ingredient_id) REFERENCES ingredients(id)
+);  
\ No newline at end of file
diff --git a/Week2/prep/w2-prep-insert-mok-data.sql b/Week2/prep/w2-prep-insert-mok-data.sql
new file mode 100644
index 000000000..05a9b7d77
--- /dev/null
+++ b/Week2/prep/w2-prep-insert-mok-data.sql
@@ -0,0 +1,98 @@
+-- ==========================================
+-- Mock data inserts for Week 2 Prep Exercise
+-- ==========================================
+
+-- 1. Cuisines
+INSERT INTO cuisines (name) VALUES
+('Japanese')
+ON CONFLICT (name) DO NOTHING;
+
+-- 2. Main ingredients
+INSERT INTO main_ingredients (name) VALUES
+('Cheese'),
+('Vegetables'),
+('Pasta'),
+('Eggs')
+ON CONFLICT (name) DO NOTHING;
+
+-- 3. Categories
+INSERT INTO categories (name) VALUES
+('Cake'),
+('No-Bake'),
+('Vegetarian'),
+('Vegan'),
+('Gluten-Free'),
+('Japanese')
+ON CONFLICT (name) DO NOTHING;
+
+-- 4. Ingredients
+INSERT INTO ingredients (name) VALUES
+('Cheese'),
+('Vegetables'),
+('Pasta'),
+('Eggs'),
+('Condensed milk'),
+('Cream Cheese'),
+('Lemon Juice'),
+('Pie Crust'),
+('Cherry Jam'),
+('Brussels Sprouts'),
+('Sesame seeds'),
+('Pepper'),
+('Salt'),
+('Olive oil'),
+('Macaroni'),
+('Butter'),
+('Flour'),
+('Milk'),
+('Shredded Cheddar cheese'),
+('Soy sauce'),
+('Sugar')
+ON CONFLICT (name) DO NOTHING;
+
+-- 5. Recipes
+INSERT INTO recipes (name, cuisine_id, main_ingredient_id) VALUES
+('No-Bake Cheesecake', NULL, 1),
+('Roasted Brussels Sprouts', NULL, 2),
+('Mac & Cheese', NULL, 3),
+('Tamagoyaki Japanese Omelette', 1, 4)
+ON CONFLICT DO NOTHING;
+
+-- 6. Recipe ↔ Categories
+INSERT INTO recipe_categories (recipe_id, category_id) VALUES
+(1, 1), (1, 2), (1, 3),
+(2, 4), (2, 5),
+(3, 3),
+(4, 3), (4, 6)
+ON CONFLICT DO NOTHING;
+
+-- 7. Recipe ↔ Ingredients
+INSERT INTO recipe_ingredients (recipe_id, ingredient_id, amount) VALUES
+-- No-Bake Cheesecake
+(1, 5, '200 ml'),
+(1, 6, '250 g'),
+(1, 7, '1 tbsp'),
+(1, 8, '1 crust'),
+(1, 9, '2 tbsp'),
+-- Roasted Brussels Sprouts
+(2, 10, '500 g'),
+(2, 7, '1 tbsp'),
+(2, 11, '1 tsp'),
+(2, 12, '1 tsp'),
+(2, 13, '1 tsp'),
+(2, 14, '2 tbsp'),
+-- Mac & Cheese
+(3, 15, '200 g'),
+(3, 16, '50 g'),
+(3, 17, '2 tbsp'),
+(3, 13, '1 tsp'),
+(3, 12, '1 tsp'),
+(3, 18, '200 ml'),
+(3, 19, '150 g'),
+-- Tamagoyaki Japanese Omelette
+(4, 4, '4'),
+(4, 20, '1 tbsp'),
+(4, 21, '1 tsp'),
+(4, 13, '1 tsp'),
+(4, 14, '1 tbsp')
+ON CONFLICT DO NOTHING;
\ No newline at end of file
diff --git a/Week2/prep/w2-request.sql b/Week2/prep/w2-request.sql
new file mode 100644
index 000000000..6e076e107
--- /dev/null
+++ b/Week2/prep/w2-request.sql
@@ -0,0 +1,24 @@
+-- 1. All vegetarian recipes with potatoes (но картошки нет в данных)
+SELECT r.name AS recipe_name
+FROM recipes r
+JOIN recipe_categories rc ON r.id = rc.recipe_id  
+JOIN categories c ON rc.category_id = c.id
+WHERE c.name = 'Vegetarian';
+
+-- 2. All cakes that do not need baking
+SELECT r.name AS recipe_name
+FROM recipes r
+JOIN recipe_categories rc1 ON r.id = rc1.recipe_id
+JOIN categories c1 ON rc1.category_id = c1.id
+JOIN recipe_categories rc2 ON r.id = rc2.recipe_id  
+JOIN categories c2 ON rc2.category_id = c2.id
+WHERE c1.name = 'Cake' AND c2.name = 'No-Bake';
+
+-- 3. All vegan and Japanese recipes
+SELECT r.name AS recipe_name
+FROM recipes r
+JOIN recipe_categories rc1 ON r.id = rc1.recipe_id
+JOIN categories c1 ON rc1.category_id = c1.id
+JOIN recipe_categories rc2 ON r.id = rc2.recipe_id
+JOIN categories c2 ON rc2.category_id = c2.id
+WHERE c1.name = 'Vegan' AND c2.name = 'Japanese';
\ No newline at end of file
diff --git a/Week4/homework/task1/README.md b/Week4/homework/task1/README.md
new file mode 100644
index 000000000..cc90d8d8b
--- /dev/null
+++ b/Week4/homework/task1/README.md
@@ -0,0 +1,11 @@
+exercise 3.1 - folder task 1
+exercise 3.1 (part 1) import - file import_csv.js
+exercises 3.1 (parts 2 and 3)- file aggregations.js
+
+
+exercises 3.2 - folder taks 2
+
+
+## Why two containers?
+1. Exercise 1: Simple MongoDB on port 27018
+2. Exercise 2: MongoDB with a replica set on port 27017 (required for transactions)
\ No newline at end of file
diff --git a/Week4/homework/task1/package-lock.json b/Week4/homework/task1/package-lock.json
new file mode 100644
index 000000000..fa2232838
--- /dev/null
+++ b/Week4/homework/task1/package-lock.json
@@ -0,0 +1,173 @@
+{
+  "name": "ex1-aggregation",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "ex1-aggregation",
+      "dependencies": {
+        "csv-parser": "^3.0.0",
+        "mongodb": "^6.0.0"
+      }
+    },
+    "node_modules/@mongodb-js/saslprep": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/@mongodb-js/saslprep/-/saslprep-1.4.0.tgz",
+      "integrity": "sha512-ZHzx7Z3rdlWL1mECydvpryWN/ETXJiCxdgQKTAH+djzIPe77HdnSizKBDi1TVDXZjXyOj2IqEG/vPw71ULF06w==",
+      "license": "MIT",
+      "dependencies": {
+        "sparse-bitfield": "^3.0.3"
+      }
+    },
+    "node_modules/@types/webidl-conversions": {
+      "version": "7.0.3",
+      "resolved": "https://registry.npmjs.org/@types/webidl-conversions/-/webidl-conversions-7.0.3.tgz",
+      "integrity": "sha512-CiJJvcRtIgzadHCYXw7dqEnMNRjhGZlYK05Mj9OyktqV8uVT8fD2BFOB7S1uwBE3Kj2Z+4UyPmFw/Ixgw/LAlA==",
+      "license": "MIT"
+    },
+    "node_modules/@types/whatwg-url": {
+      "version": "11.0.5",
+      "resolved": "https://registry.npmjs.org/@types/whatwg-url/-/whatwg-url-11.0.5.tgz",
+      "integrity": "sha512-coYR071JRaHa+xoEvvYqvnIHaVqaYrLPbsufM9BF63HkwI5Lgmy2QR8Q5K/lYDYo5AK82wOvSOS0UsLTpTG7uQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/webidl-conversions": "*"
+      }
+    },
+    "node_modules/bson": {
+      "version": "6.10.4",
+      "resolved": "https://registry.npmjs.org/bson/-/bson-6.10.4.tgz",
+      "integrity": "sha512-WIsKqkSC0ABoBJuT1LEX+2HEvNmNKKgnTAyd0fL8qzK4SH2i9NXg+t08YtdZp/V9IZ33cxe3iV4yM0qg8lMQng==",
+      "license": "Apache-2.0",
+      "engines": {
+        "node": ">=16.20.1"
+      }
+    },
+    "node_modules/csv-parser": {
+      "version": "3.2.0",
+      "resolved": "https://registry.npmjs.org/csv-parser/-/csv-parser-3.2.0.tgz",
+      "integrity": "sha512-fgKbp+AJbn1h2dcAHKIdKNSSjfp43BZZykXsCjzALjKy80VXQNHPFJ6T9Afwdzoj24aMkq8GwDS7KGcDPpejrA==",
+      "license": "MIT",
+      "bin": {
+        "csv-parser": "bin/csv-parser"
+      },
+      "engines": {
+        "node": ">= 10"
+      }
+    },
+    "node_modules/memory-pager": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/memory-pager/-/memory-pager-1.5.0.tgz",
+      "integrity": "sha512-ZS4Bp4r/Zoeq6+NLJpP+0Zzm0pR8whtGPf1XExKLJBAczGMnSi3It14OiNCStjQjM6NU1okjQGSxgEZN8eBYKg==",
+      "license": "MIT"
+    },
+    "node_modules/mongodb": {
+      "version": "6.21.0",
+      "resolved": "https://registry.npmjs.org/mongodb/-/mongodb-6.21.0.tgz",
+      "integrity": "sha512-URyb/VXMjJ4da46OeSXg+puO39XH9DeQpWCslifrRn9JWugy0D+DvvBvkm2WxmHe61O/H19JM66p1z7RHVkZ6A==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@mongodb-js/saslprep": "^1.3.0",
+        "bson": "^6.10.4",
+        "mongodb-connection-string-url": "^3.0.2"
+      },
+      "engines": {
+        "node": ">=16.20.1"
+      },
+      "peerDependencies": {
+        "@aws-sdk/credential-providers": "^3.188.0",
+        "@mongodb-js/zstd": "^1.1.0 || ^2.0.0",
+        "gcp-metadata": "^5.2.0",
+        "kerberos": "^2.0.1",
+        "mongodb-client-encryption": ">=6.0.0 <7",
+        "snappy": "^7.3.2",
+        "socks": "^2.7.1"
+      },
+      "peerDependenciesMeta": {
+        "@aws-sdk/credential-providers": {
+          "optional": true
+        },
+        "@mongodb-js/zstd": {
+          "optional": true
+        },
+        "gcp-metadata": {
+          "optional": true
+        },
+        "kerberos": {
+          "optional": true
+        },
+        "mongodb-client-encryption": {
+          "optional": true
+        },
+        "snappy": {
+          "optional": true
+        },
+        "socks": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/mongodb-connection-string-url": {
+      "version": "3.0.2",
+      "resolved": "https://registry.npmjs.org/mongodb-connection-string-url/-/mongodb-connection-string-url-3.0.2.tgz",
+      "integrity": "sha512-rMO7CGo/9BFwyZABcKAWL8UJwH/Kc2x0g72uhDWzG48URRax5TCIcJ7Rc3RZqffZzO/Gwff/jyKwCU9TN8gehA==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@types/whatwg-url": "^11.0.2",
+        "whatwg-url": "^14.1.0 || ^13.0.0"
+      }
+    },
+    "node_modules/punycode": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/punycode/-/punycode-2.3.1.tgz",
+      "integrity": "sha512-vYt7UD1U9Wg6138shLtLOvdAu+8DsC/ilFtEVHcH+wydcSpNE20AfSOduf6MkRFahL5FY7X1oU7nKVZFtfq8Fg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=6"
+      }
+    },
+    "node_modules/sparse-bitfield": {
+      "version": "3.0.3",
+      "resolved": "https://registry.npmjs.org/sparse-bitfield/-/sparse-bitfield-3.0.3.tgz",
+      "integrity": "sha512-kvzhi7vqKTfkh0PZU+2D2PIllw2ymqJKujUcyPMd9Y75Nv4nPbGJZXNhxsgdQab2BmlDct1YnfQCguEvHr7VsQ==",
+      "license": "MIT",
+      "dependencies": {
+        "memory-pager": "^1.0.2"
+      }
+    },
+    "node_modules/tr46": {
+      "version": "5.1.1",
+      "resolved": "https://registry.npmjs.org/tr46/-/tr46-5.1.1.tgz",
+      "integrity": "sha512-hdF5ZgjTqgAntKkklYw0R03MG2x/bSzTtkxmIRw/sTNV8YXsCJ1tfLAX23lhxhHJlEf3CRCOCGGWw3vI3GaSPw==",
+      "license": "MIT",
+      "dependencies": {
+        "punycode": "^2.3.1"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/webidl-conversions": {
+      "version": "7.0.0",
+      "resolved": "https://registry.npmjs.org/webidl-conversions/-/webidl-conversions-7.0.0.tgz",
+      "integrity": "sha512-VwddBukDzu71offAQR975unBIGqfKZpM+8ZX6ySk8nYhVoo5CYaZyzt3YBvYtRtO+aoGlqxPg/B87NGVZ/fu6g==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=12"
+      }
+    },
+    "node_modules/whatwg-url": {
+      "version": "14.2.0",
+      "resolved": "https://registry.npmjs.org/whatwg-url/-/whatwg-url-14.2.0.tgz",
+      "integrity": "sha512-De72GdQZzNTUBBChsXueQUnPKDkg/5A5zp7pFDuQAj5UFoENpiACU0wlCvzpAGnTkj++ihpKwKyYewn/XNUbKw==",
+      "license": "MIT",
+      "dependencies": {
+        "tr46": "^5.1.0",
+        "webidl-conversions": "^7.0.0"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    }
+  }
+}
diff --git a/Week4/homework/task1/package.json b/Week4/homework/task1/package.json
new file mode 100644
index 000000000..c8ffeb026
--- /dev/null
+++ b/Week4/homework/task1/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "ex1-aggregation",
+  "dependencies": {
+    "mongodb": "^6.0.0",
+    "csv-parser": "^3.0.0"
+  }
+}
\ No newline at end of file
diff --git a/Week4/homework/task1/scripts/aggregations.js b/Week4/homework/task1/scripts/aggregations.js
new file mode 100644
index 000000000..c579a1e03
--- /dev/null
+++ b/Week4/homework/task1/scripts/aggregations.js
@@ -0,0 +1,72 @@
+const { MongoClient } = require('mongodb');
+
+// Функция 1: Население по годам для страны   --- exercise asks for country
+async function getPopulationByYear(country) {
+  const client = new MongoClient('mongodb://localhost:27018');
+  
+  try {
+    await client.connect();
+    const collection = client.db('population_db').collection('population');
+    
+    const result = await collection.aggregate([
+      { $match: { 
+        Country: country,
+        Year: { $in: [1950, 1960, 1970, 1980, 1990, 2000, 2010, 2020, 2022] }
+      }},
+      { $group: {
+        _id: "$Year",
+        countPopulation: { $sum: { $add: ["$M", "$F"] } }
+      }},
+      { $sort: { _id: 1 } }
+    ]).toArray();
+    
+    return result;
+  } finally {
+    await client.close();
+  }
+}
+
+// Функция 2: Данные по континентам --- exercise asks for continents but data uses regions
+async function getContinentData(year, age) {
+  const client = new MongoClient('mongodb://localhost:27018');
+  
+  try {
+    await client.connect();
+    const collection = client.db('population_db').collection('population');
+    
+    const result = await collection.aggregate([
+      { $match: { 
+        Year: year,
+        Age: age,
+        Country: { 
+          $in: [
+            "AFRICA", "ASIA", "EUROPE", 
+            "LATIN AMERICA AND THE CARIBBEAN", 
+            "NORTHERN AMERICA", "OCEANIA"
+          ] 
+        }
+      }},
+      { $addFields: {
+        TotalPopulation: { $add: ["$M", "$F"] }
+      }},
+      { $sort: { Country: 1 } }
+    ]).toArray();
+    
+    return result;
+  } finally {
+    await client.close();
+  }
+}
+
+// Тестирование обеих функций  --- test if needed
+async function main() {
+  console.log('=== Population by year for Netherlands ===');
+  const netherlandsData = await getPopulationByYear("Netherlands");
+  console.log(JSON.stringify(netherlandsData, null, 2));
+  
+  console.log('\n=== Continent data for 2020, age 100+ ===');
+  const continentData = await getContinentData(2020, "100+");
+  console.log(JSON.stringify(continentData, null, 2));
+}
+
+main().catch(console.error);
\ No newline at end of file
diff --git a/Week4/homework/task1/scripts/import_csv.js b/Week4/homework/task1/scripts/import_csv.js
new file mode 100644
index 000000000..20dde4858
--- /dev/null
+++ b/Week4/homework/task1/scripts/import_csv.js
@@ -0,0 +1,35 @@
+const { MongoClient } = require('mongodb');
+const fs = require('fs');
+const csv = require('csv-parser');
+
+async function importData() {
+  const client = new MongoClient('mongodb://localhost:27018');
+  
+  try {
+    await client.connect();
+    const db = client.db('population_db');
+    const collection = db.collection('population');
+    
+    const documents = [];
+    fs.createReadStream('../../ex1-aggregation/population_pyramid_1950-2022.csv')
+      .pipe(csv())
+      .on('data', (row) => {
+        documents.push({
+          Country: row.Country,
+          Year: parseInt(row.Year),
+          Age: row.Age,
+          M: parseInt(row.M),
+          F: parseInt(row.F)
+        });
+      })
+      .on('end', async () => {
+        await collection.insertMany(documents);
+        console.log(`Imported ${documents.length} documents`);
+        await client.close();
+      });
+  } catch (error) {
+    console.error(error);
+  }
+}
+
+importData();
\ No newline at end of file
diff --git a/Week4/homework/task2/index.js b/Week4/homework/task2/index.js
new file mode 100644
index 000000000..87f8b81a4
--- /dev/null
+++ b/Week4/homework/task2/index.js
@@ -0,0 +1,27 @@
+import { setupDatabase } from './setup.js';
+import { transferMoney } from './transfer.js';
+
+async function main() {
+  // 1. Настраиваем базу данных --- setup the database
+  await setupDatabase();
+  
+  // 2. Выполняем перевод --- perform a transfer
+  await transferMoney(101, 102, 1000, "Test transfer");
+  
+  // 3. Проверяем результат --- check the result
+  const { MongoClient } = await import('mongodb');
+  const client = new MongoClient('mongodb://localhost:27017/?replicaSet=rs0&directConnection=true');
+  
+  await client.connect();
+  const collection = client.db('bank_db').collection('accounts');
+  
+  const account101 = await collection.findOne({ account_number: 101 });
+  const account102 = await collection.findOne({ account_number: 102 });
+  
+  console.log('\nAccount 101 balance:', account101.balance);
+  console.log('Account 102 balance:', account102.balance);
+  
+  await client.close();
+}
+
+main().catch(console.error);
\ No newline at end of file
diff --git a/Week4/homework/task2/package-lock.json b/Week4/homework/task2/package-lock.json
new file mode 100644
index 000000000..35bd854e1
--- /dev/null
+++ b/Week4/homework/task2/package-lock.json
@@ -0,0 +1,160 @@
+{
+  "name": "ex2-transactions",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "ex2-transactions",
+      "dependencies": {
+        "mongodb": "^6.0.0"
+      }
+    },
+    "node_modules/@mongodb-js/saslprep": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/@mongodb-js/saslprep/-/saslprep-1.4.0.tgz",
+      "integrity": "sha512-ZHzx7Z3rdlWL1mECydvpryWN/ETXJiCxdgQKTAH+djzIPe77HdnSizKBDi1TVDXZjXyOj2IqEG/vPw71ULF06w==",
+      "license": "MIT",
+      "dependencies": {
+        "sparse-bitfield": "^3.0.3"
+      }
+    },
+    "node_modules/@types/webidl-conversions": {
+      "version": "7.0.3",
+      "resolved": "https://registry.npmjs.org/@types/webidl-conversions/-/webidl-conversions-7.0.3.tgz",
+      "integrity": "sha512-CiJJvcRtIgzadHCYXw7dqEnMNRjhGZlYK05Mj9OyktqV8uVT8fD2BFOB7S1uwBE3Kj2Z+4UyPmFw/Ixgw/LAlA==",
+      "license": "MIT"
+    },
+    "node_modules/@types/whatwg-url": {
+      "version": "11.0.5",
+      "resolved": "https://registry.npmjs.org/@types/whatwg-url/-/whatwg-url-11.0.5.tgz",
+      "integrity": "sha512-coYR071JRaHa+xoEvvYqvnIHaVqaYrLPbsufM9BF63HkwI5Lgmy2QR8Q5K/lYDYo5AK82wOvSOS0UsLTpTG7uQ==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/webidl-conversions": "*"
+      }
+    },
+    "node_modules/bson": {
+      "version": "6.10.4",
+      "resolved": "https://registry.npmjs.org/bson/-/bson-6.10.4.tgz",
+      "integrity": "sha512-WIsKqkSC0ABoBJuT1LEX+2HEvNmNKKgnTAyd0fL8qzK4SH2i9NXg+t08YtdZp/V9IZ33cxe3iV4yM0qg8lMQng==",
+      "license": "Apache-2.0",
+      "engines": {
+        "node": ">=16.20.1"
+      }
+    },
+    "node_modules/memory-pager": {
+      "version": "1.5.0",
+      "resolved": "https://registry.npmjs.org/memory-pager/-/memory-pager-1.5.0.tgz",
+      "integrity": "sha512-ZS4Bp4r/Zoeq6+NLJpP+0Zzm0pR8whtGPf1XExKLJBAczGMnSi3It14OiNCStjQjM6NU1okjQGSxgEZN8eBYKg==",
+      "license": "MIT"
+    },
+    "node_modules/mongodb": {
+      "version": "6.21.0",
+      "resolved": "https://registry.npmjs.org/mongodb/-/mongodb-6.21.0.tgz",
+      "integrity": "sha512-URyb/VXMjJ4da46OeSXg+puO39XH9DeQpWCslifrRn9JWugy0D+DvvBvkm2WxmHe61O/H19JM66p1z7RHVkZ6A==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@mongodb-js/saslprep": "^1.3.0",
+        "bson": "^6.10.4",
+        "mongodb-connection-string-url": "^3.0.2"
+      },
+      "engines": {
+        "node": ">=16.20.1"
+      },
+      "peerDependencies": {
+        "@aws-sdk/credential-providers": "^3.188.0",
+        "@mongodb-js/zstd": "^1.1.0 || ^2.0.0",
+        "gcp-metadata": "^5.2.0",
+        "kerberos": "^2.0.1",
+        "mongodb-client-encryption": ">=6.0.0 <7",
+        "snappy": "^7.3.2",
+        "socks": "^2.7.1"
+      },
+      "peerDependenciesMeta": {
+        "@aws-sdk/credential-providers": {
+          "optional": true
+        },
+        "@mongodb-js/zstd": {
+          "optional": true
+        },
+        "gcp-metadata": {
+          "optional": true
+        },
+        "kerberos": {
+          "optional": true
+        },
+        "mongodb-client-encryption": {
+          "optional": true
+        },
+        "snappy": {
+          "optional": true
+        },
+        "socks": {
+          "optional": true
+        }
+      }
+    },
+    "node_modules/mongodb-connection-string-url": {
+      "version": "3.0.2",
+      "resolved": "https://registry.npmjs.org/mongodb-connection-string-url/-/mongodb-connection-string-url-3.0.2.tgz",
+      "integrity": "sha512-rMO7CGo/9BFwyZABcKAWL8UJwH/Kc2x0g72uhDWzG48URRax5TCIcJ7Rc3RZqffZzO/Gwff/jyKwCU9TN8gehA==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "@types/whatwg-url": "^11.0.2",
+        "whatwg-url": "^14.1.0 || ^13.0.0"
+      }
+    },
+    "node_modules/punycode": {
+      "version": "2.3.1",
+      "resolved": "https://registry.npmjs.org/punycode/-/punycode-2.3.1.tgz",
+      "integrity": "sha512-vYt7UD1U9Wg6138shLtLOvdAu+8DsC/ilFtEVHcH+wydcSpNE20AfSOduf6MkRFahL5FY7X1oU7nKVZFtfq8Fg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=6"
+      }
+    },
+    "node_modules/sparse-bitfield": {
+      "version": "3.0.3",
+      "resolved": "https://registry.npmjs.org/sparse-bitfield/-/sparse-bitfield-3.0.3.tgz",
+      "integrity": "sha512-kvzhi7vqKTfkh0PZU+2D2PIllw2ymqJKujUcyPMd9Y75Nv4nPbGJZXNhxsgdQab2BmlDct1YnfQCguEvHr7VsQ==",
+      "license": "MIT",
+      "dependencies": {
+        "memory-pager": "^1.0.2"
+      }
+    },
+    "node_modules/tr46": {
+      "version": "5.1.1",
+      "resolved": "https://registry.npmjs.org/tr46/-/tr46-5.1.1.tgz",
+      "integrity": "sha512-hdF5ZgjTqgAntKkklYw0R03MG2x/bSzTtkxmIRw/sTNV8YXsCJ1tfLAX23lhxhHJlEf3CRCOCGGWw3vI3GaSPw==",
+      "license": "MIT",
+      "dependencies": {
+        "punycode": "^2.3.1"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    },
+    "node_modules/webidl-conversions": {
+      "version": "7.0.0",
+      "resolved": "https://registry.npmjs.org/webidl-conversions/-/webidl-conversions-7.0.0.tgz",
+      "integrity": "sha512-VwddBukDzu71offAQR975unBIGqfKZpM+8ZX6ySk8nYhVoo5CYaZyzt3YBvYtRtO+aoGlqxPg/B87NGVZ/fu6g==",
+      "license": "BSD-2-Clause",
+      "engines": {
+        "node": ">=12"
+      }
+    },
+    "node_modules/whatwg-url": {
+      "version": "14.2.0",
+      "resolved": "https://registry.npmjs.org/whatwg-url/-/whatwg-url-14.2.0.tgz",
+      "integrity": "sha512-De72GdQZzNTUBBChsXueQUnPKDkg/5A5zp7pFDuQAj5UFoENpiACU0wlCvzpAGnTkj++ihpKwKyYewn/XNUbKw==",
+      "license": "MIT",
+      "dependencies": {
+        "tr46": "^5.1.0",
+        "webidl-conversions": "^7.0.0"
+      },
+      "engines": {
+        "node": ">=18"
+      }
+    }
+  }
+}
diff --git a/Week4/homework/task2/package.json b/Week4/homework/task2/package.json
new file mode 100644
index 000000000..1d6bb922a
--- /dev/null
+++ b/Week4/homework/task2/package.json
@@ -0,0 +1,7 @@
+{
+  "name": "ex2-transactions",
+  "type": "module",
+  "dependencies": {
+    "mongodb": "^6.0.0"
+  }
+}
\ No newline at end of file
diff --git a/Week4/homework/task2/setup.js b/Week4/homework/task2/setup.js
new file mode 100644
index 000000000..480b2cfbe
--- /dev/null
+++ b/Week4/homework/task2/setup.js
@@ -0,0 +1,61 @@
+import { MongoClient } from 'mongodb';
+
+export async function setupDatabase() {
+  const client = new MongoClient('mongodb://localhost:27017/?replicaSet=rs0&directConnection=true');
+  
+  try {
+    await client.connect();
+    const collection = client.db('bank_db').collection('accounts');
+    
+    // Очищаем коллекцию --- clear the collection
+    await collection.deleteMany({});
+    
+    // Создаем тестовые счета --- create test accounts
+    const accounts = [
+      {
+        account_number: 101,
+        balance: 10000,
+        account_changes: [
+          {
+            change_number: 1,
+            amount: 10000,
+            changed_date: new Date(),
+            remark: "Initial deposit"
+          }
+        ]
+      },
+      {
+        account_number: 102,
+        balance: 5000,
+        account_changes: [
+          {
+            change_number: 1,
+            amount: 5000,
+            changed_date: new Date(),
+            remark: "Initial deposit"
+          }
+        ]
+      },
+      {
+        account_number: 103,
+        balance: 2000,
+        account_changes: [
+          {
+            change_number: 1,
+            amount: 2000,
+            changed_date: new Date(),
+            remark: "Initial deposit"
+          }
+        ]
+      }
+    ];
+    
+    await collection.insertMany(accounts);
+    console.log('Database setup completed');
+    
+  } finally {
+    await client.close();
+  }
+}
+
+// setupDatabase();
\ No newline at end of file
diff --git a/Week4/homework/task2/transfer.js b/Week4/homework/task2/transfer.js
new file mode 100644
index 000000000..5c4892fe5
--- /dev/null
+++ b/Week4/homework/task2/transfer.js
@@ -0,0 +1,80 @@
+import { MongoClient } from 'mongodb';
+
+export async function transferMoney(fromAccount, toAccount, amount, remark) {
+  const client = new MongoClient('mongodb://localhost:27017/?replicaSet=rs0&directConnection=true');
+  
+  try {
+    await client.connect();
+    const collection = client.db('bank_db').collection('accounts');
+    
+    // Начинаем транзакцию --- start a transaction
+    const session = client.startSession();
+    
+    try {
+      const result = await session.withTransaction(async () => {
+        // 1. Проверяем существование счетов --- check account existence
+        const fromAcc = await collection.findOne(
+          { account_number: fromAccount },
+          { session }
+        );
+        const toAcc = await collection.findOne(
+          { account_number: toAccount },
+          { session }
+        );
+        
+        if (!fromAcc || !toAcc) {
+          throw new Error('Account not found');
+        }
+        
+        // 2. Проверяем достаточно ли денег на счете отправителя --- check sufficient funds
+        if (fromAcc.balance < amount) {
+          throw new Error('Insufficient funds');
+        }
+        
+        // 3. Обновляем балансы и добавляем записи об изменениях --- update balances and add change records
+        const lastChangeFrom = fromAcc.account_changes.length;
+        const lastChangeTo = toAcc.account_changes.length;
+        
+        await collection.updateOne(
+          { account_number: fromAccount },
+          {
+            $inc: { balance: -amount },
+            $push: {
+              account_changes: {
+                change_number: lastChangeFrom + 1,
+                amount: -amount,
+                changed_date: new Date(),
+                remark: remark
+              }
+            }
+          },
+          { session }
+        );
+        
+        await collection.updateOne(
+          { account_number: toAccount },
+          {
+            $inc: { balance: amount },
+            $push: {
+              account_changes: {
+                change_number: lastChangeTo + 1,
+                amount: amount,
+                changed_date: new Date(),
+                remark: remark
+              }
+            }
+          },
+          { session }
+        );
+        
+        console.log(`Transfer successful: ${amount} from ${fromAccount} to ${toAccount}`);
+      });
+      
+    } finally {
+      await session.endSession();
+    }
+    
+  } finally {
+    await client.close();
+  }
+}
\ No newline at end of file