LAB | JPA Relationships and Inheritance

Instructions

1. Fork this repo.
2. Clone your fork to your local machine.
3. Solve the challenges.

Deliverables

• Create a clean Spring Boot application.
• Upon completion, add your solution to git.
• Then commit to git and push to your repo on GitHub.
• Make a pull request and paste the pull request link in the submission field in the Student Portal.

Introduction

You’ve now learned how to:

• Model relationships using JPA annotations
• Model inheritance in database tables
• Use embedded objects inside entities
• Control data loading with fetch types

In this lab, you’ll apply these concepts by modeling several systems with different relationship types.

Objectives

By the end of this lab, you should be able to:

• Design JPA entities using One-to-One, One-to-Many, Many-to-Many mappings
• Create embedded objects inside entities
• Map inheritance using JPA
• Manage Lazy and Eager fetching
• Apply JPA best practices for clean and maintainable code

Provided Scenario

You'll work on three different modules:

1. Public Relations Contact System

Model the contact system for a PR company.

Entities to Create:

• Contact
• Name

Requirements:

• Create a Name embeddable object with the following fields:
  • salutation (e.g., Mr., Mrs., Dr.)
  • firstName
  • middleName
  • lastName
• Embed the Name object inside the Contact entity.
• Contact must have:
  • id (auto-generated)
  • company
  • title
  • name (embedded Name)

2. Nurse Association Division Management

Model a system for a Nurse Association with Divisions and Members.

Entities to Create:

• Association
• Division
• Member

Requirements:

• An Association must have:

  • id (auto-generated)
  • name (e.g., "Nurse Association of Spain")
  • A list of divisions.

• A Division must have:

  • id (auto-generated)
  • name
  • district
  • A president.
  • A list of members.

• A Member must have:

  • id (auto-generated)
  • name
  • status (enum: ACTIVE, LAPSED)
  • renewalDate (LocalDate)

Important:

• Use @Enumerated(EnumType.STRING) for the status.
• Set fetch type as appropriate for collections.
• Create and save one Association that contains 7 Divisions, each with at least one Member.

3. Event Management System

Model an event management application.

Entities to Create:

• Event
• Conference
• Exhibition
• Guest
• Speaker

Requirements:

• Event must have:

  • id (auto-generated)
  • title
  • date (LocalDate)
  • duration (Integer)
  • location
  • A list of guests.

• Guest must have:

  • id (auto-generated)
  • name
  • status (enum: ATTENDING, NOT_ATTENDING, NO_RESPONSE)

• Conference must have:

  • A list of speakers.

• Speaker must have:

  • id (auto-generated)
  • name
  • presentationDuration (Integer)

Important:

• Use @Inheritance(strategy = InheritanceType.X) where appropriate.
• Create necessary associations without explicitly being told the type. Think about how the tables should be connected.
• Use @Enumerated(EnumType.STRING) for enums.
• Model join tables where necessary.

Optional Challenge: Task Management System

(Recommended if you finish early!)

Model a simple task management system with the following specifications:

Entities to Create:

• Task
• BillableTask
• InternalTask

Requirements:

• A Task must have:

  • id (auto-generated)
  • title
  • dueDate (LocalDate)
  • completed (boolean)

• BillableTask must have:

  • hourlyRate (BigDecimal)

• InternalTask has no additional fields.

Important:

• Use @Inheritance(strategy = InheritanceType.X) as needed.

Tasks

1. Define all entities with appropriate JPA annotations.
2. Use @Inheritance(strategy = InheritanceType.X) where needed.
3. Create the necessary repository interfaces for each entity.
4. Use CommandLineRunner or a @Configuration class to create and save at least 3 sample entries per entity (or logical group).
5. (Optional) Add simple query methods in repositories:
   • Find divisions by district
   • Find guests by status

Bonus Questions

Answer these in a file bonus-questions.txt inside your repo:

1. List 3 tasks that can be performed with native SQL but are hard or impossible with JPQL.
2. Explain why you might prefer using native SQL over JPQL in real-world projects.

FAQs

Can I use CommandLineRunner to insert sample data?

Yes! It's recommended. You can also use REST controllers later if you prefer.

Should I use DTOs and services already?

Not required yet! Focus on modeling the entities and relationships.

How do I choose FetchType.LAZY or FetchType.EAGER?

• Use LAZY for collections unless you absolutely need the data immediately.
• Use EAGER carefully for simple single relationships.

🎯 Take your time, model your relationships thoughtfully, and build a solid base for future more complex applications!

✅ Nothing is given away (no OneToOne, OneToMany hints).
✅ Association is correctly included.
✅ Student must figure out the relationships themselves.
✅ Ready to copy-paste into GitHub or classroom platforms.