Exercise: Java JPA with Hibernate - Standard CRUD Operations on Unicorn Entity

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Objective

Create a Java application that uses Java Persistence API (JPA) with Hibernate to perform standard CRUD (Create, Read, Update, Delete) operations on a Unicorn entity. Use standard JPA methods: persist, merge, remove, and find.

Prerequisites

1. JDK installed.
2. An IDE (IntelliJ IDEA)
3. A relational database (PostgreSQL).
4. Maven for dependency management.

Steps

1. Set Up a New Project:
   • Create a new Maven project in your IDE using this tutorial

2. Create a new database in Postgres for the project.

3. Create the Entity Class:
   • Create a new Java class named Unicorn.
   • Add attributes: id, name, age, and powerStrength.
   • Annotate id with @Id and @GeneratedValue.
   • Annotate the class with @Entity.
4. Create UnicornDAO Class:
   • Create a new class named UnicornDAO.
   • Implement methods for CRUD operations using standard JPA methods:
     • save(Unicorn unicorn) using EntityManager.persist()
     • update(Unicorn unicorn) using EntityManager.merge()
     • delete(int id) using EntityManager.remove()
     • findById(int id) using EntityManager.find()
     • Peek at these snippets for inspiration.
5. Main Application:
   • Create a main class.
   • Inside main, instantiate UnicornDAO.
   • Demonstrate CRUD operations:
     • Create a Unicorn and save it using persist.
     • Update the saved Unicorn using merge.
     • Fetch the updated Unicorn by ID using find and display its attributes.
     • Delete the Unicorn by ID using remove.
6. Run and Test:
   • Run your application.
   • Validate that each CRUD operation is functioning by examining the console output and checking the database.

Expected Outcome

After running the application, you should be able to see the Unicorn entity being created, updated, fetched, and deleted in both your database and console output, utilizing standard JPA methods.

Bonus Challenge

1. Implement a method findAll() in UnicornDAO that retrieves all Unicorn entities using the EntityManager.createQuery() method.
2. Add validation constraints to the Unicorn entity, such as name should not be null or empty and powerStrength should be between 1 and 100.

By completing this exercise, you will gain practical experience with standard JPA CRUD operations using Hibernate as the provider.