Sequelize Model Instance

Introduction
In Sequelize, a popular Node.js ORM for relational databases like MySQL, PostgreSQL, SQLite, and others, Model Instances represent individual records (rows) within a table in your database.
In Sequelize, model instances represent individual records in a table. They encapsulate both the data for the record and methods to interact with that record within the database, providing a powerful way to work with data in a more object-oriented manner.

Model Definition
A model in Sequelize corresponds to a table in the database. You define a model by extending Sequelize's Model class and specifying the attributes (columns) of the table.

 const { Sequelize, DataTypes, Model } = require('sequelize');
 const sequelize = new Sequelize('database_name', 'username', 'password', {
    host: 'localhost',
    dialect: 'postgres',
    port: 5432,  // The default port for PostgreSQL
  });

 const User = sequelize.define(
   'User',
   {
     // Model attributes are defined here
     firstName: {
       type: DataTypes.STRING,
       allowNull: false,
     },
     lastName: {
       type: DataTypes.STRING,
       // allowNull defaults to true
     }
   },
   {
     // Other model options
     sequelize, // pass the sequelize instance
     modelName: 'User' // Name of the model
   },
 );

Creating an Instance

A model instance is created by calling the create method or by instantiating a new instance using new Model() and then saving it.

 // Using create method
 const user = await User.create({ firstName: 'John', lastName: 'Doe' });
 console.log(user instanceof User); // true
 console.log(user.firstName); // "John"

Instance Methods

Model instances come with built-in methods for interacting with the database, such as save, destroy, and update.

You can also define custom instance methods within the model definition.

 // Built-in methods
 user.lastName = 'Smith';
 await user.save(); // Updates the record in the database
 await user.destroy(); // Deletes the record from the database

Reloading an Instance

If you need to refresh an instance with the latest data from the database, you can use the reload method.

 await user.reload();

Validations

Sequelize allows you to define validations on model attributes. These validations are automatically run before an instance is saved.

 User.init({
   firstName: {
     type: DataTypes.STRING,
     allowNull: false,
     validate: {
       notEmpty: true
     }
   },
 });

Instance Scopes

You can define scopes to automatically include certain conditions or attributes in your queries when working with model instances.

 const users = await User.scope('active').findAll();