JPA & Hibernate

Object-Relational Mapping (ORM) and Entities

Modern Java applications utilize Object-Relational Mapping (ORM) technologies to translate language objects and classes into database tables and rows.

---

1. Difference between JPA and Hibernate

There is a fundamental distinction between the specification standard and its concrete implementation engine:

Clic para ampliar

Detailed Persistence Diagram Explanation

1. JPA (Jakarta Persistence API): A Java specification defining annotations (@Entity, @Id, @Column) and contracts without containing executable logic.
2. Hibernate ORM: The default concrete engine chosen by Spring Boot. Reads JPA annotations, translates object operations into SQL dialect statements, and manages persistence sessions.
3. Relational Database: Physical storage engine where tabular data resides.

---

2. JPA Entity Mapping and Annotations

An Entity is a POJO (Plain Old Java Object) representing a physical table. Each class instance corresponds to a row in the table.

2.1. Core Mapping Annotations

Annotation	Purpose	Common Attributes
@Entity	Declares the Java class as a JPA-managed entity.	name (logical entity name in JPQL)
@Table	Specifies physical database table name.	name, schema, uniqueConstraints
@Id	Marks field as Primary Key.	N/A
@GeneratedValue	Specifies automatic primary key generation strategy.	strategy (IDENTITY, SEQUENCE, AUTO, TABLE)
@Column	Configures column mapping details.	name, nullable, unique, length, precision
@JoinColumn	Defines Foreign Key column name in relationships.	name, referencedColumnName, nullable
@Transient	Specifies field should NOT be persisted in storage.	N/A

---

3. Relational Database Model (ER Diagram)

Before writing Java code, we design the relational database schema for a product catalog domain:

Clic para ampliar

Detailed ER Diagram Explanation

• CATEGORIES: Parent table storing product classifications (1 to N with PRODUCTS).
• SUPPLIERS: Parent table storing supplier companies (1 to N with PRODUCTS).
• PRODUCTS: Main table containing two Foreign Keys (FK): category_id and supplier_id, physically referencing primary keys (PK) of parent tables.

---

4. Complete Java Entity Mapping with JPA and Lombok

Below, the ER diagram is mapped into Java entity classes using JPA and Lombok annotations:

4.1. Entity Category (Table categorias)

src/main/java/com/icesi/app/model/Category.java

package com.icesi.app.model;

import jakarta.persistence.*;
import lombok.*;

@Entity
@Table(name = "categorias")
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Category {

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

    @Column(name = "nombre", nullable = false, length = 80)
    private String name;

    @Column(name = "descripcion", length = 255)
    private String description;
}

4.2. Entity Supplier (Table proveedores)

src/main/java/com/icesi/app/model/Supplier.java

package com.icesi.app.model;

import jakarta.persistence.*;
import lombok.*;

@Entity
@Table(name = "proveedores")
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Supplier {

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

    @Column(name = "nombre_empresa", nullable = false, length = 100)
    private String companyName;

    @Column(name = "nit_ruc", unique = true, nullable = false, length = 50)
    private String taxId;
}

4.3. Entity Product with @ManyToOne Relationships (Table productos)

src/main/java/com/icesi/app/model/Product.java

package com.icesi.app.model;

import jakarta.persistence.*;
import lombok.*;

@Entity
@Table(name = "productos")
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Product {

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

    @Column(name = "nombre_producto", nullable = false, length = 120)
    private String name;

    @Column(name = "precio", nullable = false, precision = 10, scale = 2)
    private Double price;

    @Column(name = "codigo_sku", unique = true, nullable = false, length = 50)
    private String sku;

    // Transient field ignored by JPA
    @Transient
    private String temporaryDiscountCode;

    // Many-to-One: Many products belong to one Category
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "categoria_id", nullable = false)
    private Category category;

    // Many-to-One: Many products are supplied by one Supplier
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "proveedor_id", nullable = false)
    private Supplier supplier;
}

---

Self-Assessment Quiz

Cargando cuestionario...