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Exercise 7 - Movie Details and Relationships

In this exercise, we'll create a movie detail page and use JPA annotations to model the relationships between movies, cast members, people, and jobs.

You will learn to:

  • Look up a single entity by its id
  • Use @ManyToOne and @OneToMany JPA annotations to model relationships
  • Navigate relationships between entities

7.1 Link to movie details

📖 We want to be able to click on a movie in the list and display more details about that movie. There should be a separate page for movie details, and that page needs its own URL. The URL for the movies page is http://localhost:8080/movies, so it would be natural to use http://localhost:8080/movies/11 for a movie with id = 11.

✏️ Create a link to the details page for each movie in movie-list.jsp. Then, in MoviesController.show(), use the id parameter to look up the correct movie from the MovieRepository and pass it along to the ModelAndView.

💡 Hint

The syntax for linking to a page on the same host is <a href="/movies/${movie.id}">${movie.name}</a>

7.2 Show the cast of a movie

📖 There are lots of people involved in making a movie, and each person can be involved in several different movies, doing different jobs. This is represented by the casts table in the database, by connecting a person, a movie and a job.

Casts ER diagram

When looking at one particular movie in the database, you can follow the relationship between the movies and the casts table to find all the people involved in that movie. This is a One-to-Many relationship, since one movie can have many casts, while one particular row in the casts table refers to only one movie. In JPA, this is described with the @OneToMany annotation.

📖 Example — a relationship between cars and their owners:

@Entity
class Person {
  @Id
  Long id;

  @OneToMany(mappedBy = "owner") //refers to the java property name "owner" in the Car class
  List<Car> cars;
}

class Car {
  @Id
  Long id;

  @ManyToOne
  @JoinColumn("owner_person_id") //refers to the database column "owner_person_id" in the table "car"
  Person owner;
}

In this example, one Person can own many Cars, so this is a @OneToMany relationship as seen from the Person side. On the other hand, one Car can only have a single Person as its owner, so this is a @ManyToOne relationship.

✏️ Use the @ManyToOne and @OneToMany annotations to connect the Movie and Cast classes, the Person and Cast classes, and the Job and Cast classes. Try out the movie detail page and you should see the cast of the movie.

💡 Hint

In this database, the relationship between movie and casts is a one-to-many relationship. One movie is related to several casts. And inversely the relation between casts and movie is a many-to-one relation.

Casts also have a many-to-one relation to job and person.

7.3 Show the director

📖 You should now have a property List<Cast> casts in the Movie class. One of the cast members in that list has a Job with the name "Director".

✏️ Implement the getDirector() method in Movie so that it returns the Person who was the director. Then, display the name of that person in the movie-list.jsp page in the "Director" column.

✏️ Now that you have the director of a movie, create a link to a page that shows more details about that person. The URL should be http://localhost:8080/directors/1 for a person with id=1.

Go to exercise 8 ➡️