Exercise 01: Value Objects with @Embeddable

Learning Objective

Learn how to use @Embeddable and @Embedded to create value objects that encapsulate related fields within an entity.

Background

Value objects are classes that represent a concept or measurement but don't have their own identity. They're stored in the same table as the owning entity.

In our movie database, instead of storing a simple rating number, we want to store both a score (e.g., 8.5) and the number of votes (e.g., 15000). These two values belong together and form a "Rating" concept.

Your Task

Create a Rating value object and embed it in the Movie entity.

Step 1: Create the Rating Class

Create a new class Rating.java in the entity package:

package com.example.moviedb.entity;

import jakarta.persistence.Embeddable;

@Embeddable
public class Rating {
    private Double score;      // e.g., 8.5
    private Integer voteCount; // e.g., 15000

    // TODO: Add default constructor
    
    // TODO: Add constructor with parameters
    
    // TODO: Add getters and setters
}

Requirements:

• The class must be annotated with @Embeddable
• Add a default constructor (required by JPA)
• Add a constructor that takes score and voteCount
• Add getters and setters for both fields

Step 2: Embed Rating in Movie Entity

Modify the Movie entity to include the Rating:

@Entity
public class Movie {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String title;
    private Integer releaseYear;
    private String genre;

    // TODO: Add the embedded Rating field here
    
    // Remember to update constructors if needed
    // Add getter and setter for rating
}

Hint: Use the @Embedded annotation on the rating field.

Testing Your Implementation

1. Restart your application (the database will be recreated)

2. Create a movie with a rating (using .http in IntelliJ):

   ### CREATE MOVIE
   POST http://localhost:8080/api/movies
   Content-Type: application/json
   
   {
       "title": "The Shawshank Redemption",
       "releaseYear": 1994,
       "genre": "Drama",
       "rating": {
           "score": 9.3,
           "voteCount": 2500000
       }
   }

3. Retrieve the movie:

   ### GET MOVIES BY ID
   GET http://localhost:8080/api/movies/1

You should see the rating embedded in the movie JSON response.

4. Check the H2 console at http://localhost:8080/h2-console and verify that the MOVIE table has columns score and vote_count (not a separate table!).

Expected Result

The Rating fields should be stored directly in the MOVIE table as separate columns. When you retrieve a movie, the rating should appear as a nested object in the JSON.

Questions to Consider

1. Why doesn't Rating need an @Id field?
2. What happens in the database? How many tables are created?
3. When would you use @Embeddable vs creating a separate entity?

Continue to Exercise 02 to add relationships between entities!