How properties of a class are mapped to the columns of a database table in Hibernate?

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Hibernate uses annotations or XML configuration files to map class properties (fields) to columns in a database table. This mapping is part of the ORM process, where Hibernate translates Java objects into database records and vice versa. The key components involved in this mapping include:

  1. Entity Class:

A class annotated with @Entity represents a table in the database.
2. Table Mapping:

The @Table annotation specifies the table name if it differs from the class name.
3. Column Mapping:

The @Column annotation specifies the mapping between a class property and a database column.
4. Primary Key Mapping:

The @Id annotation designates a property as the primary key for the entity.

How is it used?

  1. Defining the Entity Class:

Annotate the class with @Entity and optionally specify the table name using @Table.

   import javax.persistence.Entity;
   import javax.persistence.Table;
@Entity  

@Table(name = "employee")


public class Employee {


// Class properties and methods


}

  1. Mapping Properties to Columns:

Use @Column to map class properties to specific columns in the database table.

   import javax.persistence.Column;
   import javax.persistence.Id;
   import javax.persistence.Entity;
   import javax.persistence.Table;
@Entity  

@Table(name = "employee")


public class Employee {

@Id
@Column(name = "employee_id")
private int id;

@Column(name = "employee_name")
private String name;

@Column(name = "employee_salary")
private double salary;

// Getters and Setters


}

  1. Mapping Primary Key:

The @Id annotation is used to mark the primary key field of the entity.

   @Id
   @Column(name = "employee_id")
   private int id;

  1. Additional Configurations:

Hibernate provides additional annotations and configurations for advanced mappings, such as @GeneratedValue for auto-generating primary key values, @OneToMany for relationships, and @Temporal for date/time mappings.

Example:

import javax.persistence.Entity;
import javax.persistence.Table;
import javax.persistence.Column;
import javax.persistence.Id;
@Entity  

@Table(name = "employee")


public class Employee {

@Id
@Column(name = "employee_id")
private int id;

@Column(name = "employee_name")
private String name;

@Column(name = "employee_salary")
private double salary;

// Constructors, Getters, and Setters


}

Advantages of Using Hibernate for Mapping:

  • Consistency: Ensures that your object model remains consistent with the database schema.
  • Simplicity: Simplifies database operations by allowing you to work with Java objects instead of raw SQL.
  • Flexibility: Provides options for advanced mappings and relationships, making it adaptable to complex data models.
  • Maintainability: Reduces boilerplate code and improves the maintainability of the codebase by managing the database interactions through entity classes.