MongoDB

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mongosh                     # Connect to local MongoDB
mongosh "mongodb://host:port/db"  # Connect to remote

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show dbs                    // List all databases
use myDatabase              // Switch to/create database
db.dropDatabase()           // Delete current database

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show collections            // List collections
db.createCollection("users") // Create collection
db.users.drop()             // Delete collection

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// Insert one document
db.users.insertOne({
  name: "John",
  age: 30,
  email: "john@example.com",
});

// Insert multiple documents
db.users.insertMany([
  { name: "Alice", age: 25 },
  { name: "Bob", age: 35 },
]);

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// Find all documents
db.users.find();

// Find with condition
db.users.find({ age: 30 });

// Find one document
db.users.findOne({ name: "John" });

// Comparison operators
db.users.find({ age: { $gt: 25 } }); // Greater than
db.users.find({ age: { $gte: 25 } }); // Greater than or equal
db.users.find({ age: { $lt: 30 } }); // Less than
db.users.find({ age: { $lte: 30 } }); // Less than or equal
db.users.find({ age: { $ne: 30 } }); // Not equal

// Logical operators
db.users.find({ $and: [{ age: { $gt: 20 } }, { age: { $lt: 40 } }] });
db.users.find({ $or: [{ name: "John" }, { name: "Alice" }] });

// Projection (select specific fields)
db.users.find({}, { name: 1, email: 1, _id: 0 });

// Sorting
db.users.find().sort({ age: 1 }); // Ascending
db.users.find().sort({ age: -1 }); // Descending

// Limit and skip
db.users.find().limit(5);
db.users.find().skip(10).limit(5);

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// Update one document
db.users.updateOne({ _id: ObjectId("507f1f77bcf86cd799439011") }, { $set: { age: 31 } });

// Update multiple documents
db.users.updateMany({ age: { $lt: 30 } }, { $set: { status: "young" } });

// Replace entire document
db.users.replaceOne(
  { _id: ObjectId("507f1f77bcf86cd799439011") },
  { name: "John", age: 31, city: "New York" },
);

// Update operators
db.users.updateOne({ name: "John" }, { $inc: { age: 1 } }); // Increment
db.users.updateOne({ name: "John" }, { $unset: { email: "" } }); // Remove field
db.users.updateOne({ name: "John" }, { $push: { tags: "new" } }); // Add to array

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// Delete one document
db.users.deleteOne({ _id: ObjectId("507f1f77bcf86cd799439011") });

// Delete multiple documents
db.users.deleteMany({ age: { $lt: 20 } });

// Delete all documents
db.users.deleteMany({});

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// Create index
db.users.createIndex({ email: 1 });

// Create unique index
db.users.createIndex({ email: 1 }, { unique: true });

// List indexes
db.users.getIndexes();

// Drop index
db.users.dropIndex("email_1");

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npm install mongodb

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const { MongoClient } = require("mongodb");

const uri = "mongodb://localhost:27017";
const client = new MongoClient(uri);

async function connect() {
  try {
    await client.connect();
    console.log("Connected to MongoDB");
    const db = client.db("myDatabase");
    return db;
  } catch (error) {
    console.error("Connection error:", error);
  }
}

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const { MongoClient } = require("mongodb");

const uri = "mongodb://localhost:27017";
const client = new MongoClient(uri);

async function main() {
  try {
    await client.connect();
    const db = client.db("myDatabase");
    const users = db.collection("users");

    // Insert
    const insertResult = await users.insertOne({
      name: "John",
      age: 30,
      email: "john@example.com",
    });
    console.log("Inserted:", insertResult.insertedId);

    // Find
    const user = await users.findOne({ name: "John" });
    console.log("Found:", user);

    // Find all with cursor
    const cursor = users.find({ age: { $gte: 25 } });
    const allUsers = await cursor.toArray();
    console.log("All users:", allUsers);

    // Update
    const updateResult = await users.updateOne(
      { name: "John" },
      { $set: { age: 31 } },
    );
    console.log("Updated:", updateResult.modifiedCount);

    // Delete
    const deleteResult = await users.deleteOne({ name: "John" });
    console.log("Deleted:", deleteResult.deletedCount);
  } finally {
    await client.close();
  }
}

main().catch(console.error);

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const express = require("express");
const { MongoClient, ObjectId } = require("mongodb");

const app = express();
app.use(express.json());

const uri = "mongodb://localhost:27017";
const client = new MongoClient(uri);

let db;

// Connect on startup
client.connect().then(() => {
  db = client.db("myDatabase");
  console.log("Connected to MongoDB");
});

// GET all users
app.get("/users", async (req, res) => {
  const users = await db.collection("users").find().toArray();
  res.json(users);
});

// GET user by ID
app.get("/users/:id", async (req, res) => {
  const user = await db.collection("users").findOne({
    _id: new ObjectId(req.params.id),
  });
  if (!user) return res.status(404).json({ error: "User not found" });
  res.json(user);
});

// POST create user
app.post("/users", async (req, res) => {
  const result = await db.collection("users").insertOne(req.body);
  res.status(201).json({ id: result.insertedId });
});

// PUT update user
app.put("/users/:id", async (req, res) => {
  const result = await db
    .collection("users")
    .updateOne({ _id: new ObjectId(req.params.id) }, { $set: req.body });
  res.json({ modified: result.modifiedCount });
});

// DELETE user
app.delete("/users/:id", async (req, res) => {
  const result = await db.collection("users").deleteOne({
    _id: new ObjectId(req.params.id),
  });
  res.json({ deleted: result.deletedCount });
});

app.listen(3000, () => console.log("Server running on port 3000"));

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npm install mongoose

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const mongoose = require("mongoose");

// Connect
mongoose.connect("mongodb://localhost:27017/myDatabase");

// Define schema
const userSchema = new mongoose.Schema({
  name: { type: String, required: true },
  age: { type: Number, min: 0 },
  email: { type: String, unique: true },
  createdAt: { type: Date, default: Date.now },
});

// Create model
const User = mongoose.model("User", userSchema);

// CRUD operations
async function main() {
  // Create
  const user = new User({ name: "John", age: 30, email: "john@example.com" });
  await user.save();

  // Read
  const users = await User.find({ age: { $gte: 25 } });
  const john = await User.findOne({ name: "John" });

  // Update
  await User.updateOne({ name: "John" }, { age: 31 });
  // or
  john.age = 31;
  await john.save();

  // Delete
  await User.deleteOne({ name: "John" });
}

main().catch(console.error);