Databases are essential components in modern web applications, providing a way to store, retrieve, and manage data efficiently. In this section, we will cover the basics of databases, their types, and how they integrate with Node.js applications.

1. What is a Database?

   • A database is an organized collection of data, generally stored and accessed electronically from a computer system.
   • Databases are managed by Database Management Systems (DBMS).

2. Types of Databases:

   • Relational Databases (SQL):
     • Use structured query language (SQL) for defining and manipulating data.
     • Data is stored in tables with rows and columns.
     • Examples: MySQL, PostgreSQL, SQLite.
   • Non-Relational Databases (NoSQL):
     • Do not use SQL as their primary query language.
     • Data can be stored in various formats like key-value pairs, documents, graphs, or wide-column stores.
     • Examples: MongoDB, Redis, Cassandra.

3. Database Operations:

   • CRUD Operations:
     • Create: Insert new data into the database.
     • Read: Retrieve data from the database.
     • Update: Modify existing data in the database.
     • Delete: Remove data from the database.

4. Connecting to Databases in Node.js:

   • Node.js can connect to both SQL and NoSQL databases using various libraries and drivers.
   • Common libraries include mysql, pg (PostgreSQL), mongoose (MongoDB), and sequelize (ORM for SQL databases).

1. Install MongoDB:

   • Follow the installation instructions for your operating system from the official MongoDB website.

2. Start MongoDB:

   • Run the MongoDB server using the command:

     mongod
     

Mongoose is an Object Data Modeling (ODM) library for MongoDB and Node.js. It provides a straightforward, schema-based solution to model your application data.

1. Install Mongoose:

   npm install mongoose
   

1. Create a new Node.js project:

   mkdir my-database-app
   cd my-database-app
   npm init -y
   

2. Create a file named app.js and add the following code:

   const mongoose = require('mongoose');
   
   // Connect to MongoDB
   mongoose.connect('mongodb://localhost:27017/mydatabase', {
     useNewUrlParser: true,
     useUnifiedTopology: true,
   });
   
   // Define a schema
   const userSchema = new mongoose.Schema({
     name: String,
     email: String,
     age: Number,
   });
   
   // Create a model
   const User = mongoose.model('User', userSchema);
   
   // Create a new user
   const newUser = new User({
     name: 'John Doe',
     email: '[email protected]',
     age: 30,
   });
   
   // Save the user to the database
   newUser.save((err) => {
     if (err) {
       console.error('Error saving user:', err);
     } else {
       console.log('User saved successfully!');
     }
     // Close the connection
     mongoose.connection.close();
   });
   

• Connecting to MongoDB:

  mongoose.connect('mongodb://localhost:27017/mydatabase', {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  });
  

  This line connects to a MongoDB instance running on localhost at port 27017 and uses a database named mydatabase.

• Defining a Schema:

  const userSchema = new mongoose.Schema({
    name: String,
    email: String,
    age: Number,
  });
  

  A schema defines the structure of the documents within a collection. Here, we define a User schema with name, email, and age fields.

• Creating a Model:

  const User = mongoose.model('User', userSchema);
  

  A model is a compiled version of the schema, which provides an interface to interact with the database.

• Creating and Saving a Document:

  const newUser = new User({
    name: 'John Doe',
    email: '[email protected]',
    age: 30,
  });
  
  newUser.save((err) => {
    if (err) {
      console.error('Error saving user:', err);
    } else {
      console.log('User saved successfully!');
    }
    mongoose.connection.close();
  });
  

  We create a new User document and save it to the database. If the save operation is successful, a success message is logged; otherwise, an error message is displayed.

1. Set up a MongoDB database and connect to it using Mongoose.
2. Define a schema for a Product with fields: name, price, and category.
3. Create a new product and save it to the database.

1. Install MongoDB and Mongoose (if not already installed).

2. Create a new Node.js project and add the following code to app.js:

   const mongoose = require('mongoose');
   
   // Connect to MongoDB
   mongoose.connect('mongodb://localhost:27017/mydatabase', {
     useNewUrlParser: true,
     useUnifiedTopology: true,
   });
   
   // Define a schema
   const productSchema = new mongoose.Schema({
     name: String,
     price: Number,
     category: String,
   });
   
   // Create a model
   const Product = mongoose.model('Product', productSchema);
   
   // Create a new product
   const newProduct = new Product({
     name: 'Laptop',
     price: 999.99,
     category: 'Electronics',
   });
   
   // Save the product to the database
   newProduct.save((err) => {
     if (err) {
       console.error('Error saving product:', err);
     } else {
       console.log('Product saved successfully!');
     }
     // Close the connection
     mongoose.connection.close();
   });
   

• Ensure MongoDB is running: Make sure the MongoDB server is running before attempting to connect.
• Check connection string: Verify the connection string is correct and matches your MongoDB setup.
• Handle errors: Always handle errors when performing database operations to avoid crashes and ensure smooth operation.

In this section, we introduced the concept of databases, their types, and how to connect to a MongoDB database using Mongoose in a Node.js application. Understanding these basics is crucial for building robust and scalable applications. In the next section, we will dive deeper into using MongoDB with Mongoose, exploring more advanced features and operations.