Hibernate Mapping

In the previous lesson, you learned what Hibernate is and why it is used. Now it is time to understand how Hibernate maps Java classes to database tables.

This lesson is very important because incorrect mapping leads to performance issues, data inconsistency, and hard-to-debug errors in real projects.

What Is Hibernate Mapping?

Hibernate mapping is the process of connecting:

• Java classes → Database tables
• Class fields → Table columns
• Object relationships → Table relationships

Once mapping is done correctly, Hibernate automatically handles SQL generation.

Basic Class-to-Table Mapping

The simplest mapping is mapping a Java class to a single table.

@Entity
@Table(name = "users")
public class User {

    @Id
    private int id;

    private String name;
    private String email;
}

Here:

• @Entity marks the class as a table
• @Table specifies the table name
• Each field becomes a column automatically

Primary Key Mapping

Every table must have a primary key. Hibernate uses the @Id annotation for this.

In most real-world applications, IDs are auto-generated.

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;

This tells Hibernate to let the database generate unique IDs.

Column Mapping

By default, Hibernate maps field names directly to column names.

You can customize column behavior using @Column.

@Column(name = "user_email", nullable = false, unique = true)
private String email;

This ensures the email column is unique and cannot be null.

Real-World Example

Consider an employee management system:

• Employee class → employee table
• Fields → name, salary, department
• Hibernate handles insert and fetch automatically

Developers work with objects, not SQL queries.

Mapping Relationships Overview

Real applications rarely have single tables. They have relationships between tables.

Hibernate supports:

• One-to-One
• One-to-Many
• Many-to-One
• Many-to-Many

We will explore these in the next lesson.

Why Proper Mapping Matters

• Improves performance
• Reduces database errors
• Makes code easier to maintain
• Prevents data inconsistency

Good Hibernate mapping is a sign of a skilled backend developer.

Common Beginner Mistakes

Some common mistakes developers make:

• Missing primary key
• Incorrect column names
• Overusing annotations
• Poor naming conventions

Avoiding these early saves time later.

Industry Perspective

Most enterprise applications have dozens or hundreds of entity classes.

Clean and consistent mapping is critical for long-term success.

What Comes Next?

In the next lesson, you will learn how to perform CRUD operations using Hibernate.

You will finally store, update, and delete real data from the database.