Create the Category Entity

In our previous lesson, we created the User entity as the foundation for user management.

Now we'll implement the Category entity, which will provide a way to organize blog posts into broad groups.

Understanding Categories in Blog Systems

Blog categories serve as high-level containers that group related content together.

Categories differ from tags in that they represent broad, predefined classifications rather than flexible, user-defined keywords.

Implementing the Category Entity

Here's our initial implementation:

package com.devtiro.blog.domain.entities;

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

import java.util.ArrayList;
import java.util.Objects;
import java.util.Set;
import java.util.UUID;

@Entity
@NoArgsConstructor
@AllArgsConstructor
@Getter
@Setter
@Builder
@Table(name = "categories")
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private UUID id;

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

    // Custom equals implementation needed to avoid Lombok's implementation
    // which can cause issues with JPA entity lifecycle management
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Category category = (Category) o;
        return Objects.equals(id, category.id) &&
               Objects.equals(name, category.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }
}

Summary

Categories provide a hierarchical organization structure for blog content
Custom equals and hashCode methods ensure proper JPA entity behavior
The unique constraint on category names prevents duplicates
Using UUID as the primary key supports distributed systems and security