EntityA with List<EntityB>. How to make it with database

[hallow anvil]

I fried my brain while trying to understand this.

@Entity
public class Library {
  private Long id;
  private String address;
  private List<Book> books;
}

@Entity
public class Book {
  private Long id;
  private String name;
}

@Controller
public class LibraryController {
  public List<Book> findALlBooks() {
    libraryService.findAllBooks();
  }
}

Have no idea how to make it. + how db should look like

[fading merlin]

Detected code, here are some useful tools:

<@&987246584574140416> please have a look, thanks.

[thin crane]

you might want to look into one to many relationships

like one-to-many and many-to-one

[hallow anvil]

Uh okay, one more question. What if Book will be abstract class and ill inheritance next class for example:```
public class Guide extends Book {

}```
Can i still get all books?

[thin crane]

this might be helpful in that case: https://www.baeldung.com/hibernate-inheritance
but I would usually avoid that, not sure if thats commonly done in reallife situations

[hallow anvil]

1 more question my friend. What type of variable should i declare in mysql database as list? I did ManyToOne List<Book> but how Library column books should look like? Or i shouldnt create any column in Library for list of books?

[tribal hedge]

How does that work? I want to create some databases with different types of entities for example an "Event" which also has a List<Visitor> in it. How can I do that?

[raven creek]

What do you mean? As Squid said that's a one-to-many.

Or in this case a many-to-many dependant on how you define a visitor.

[fading merlin]

@hallow anvil

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[tribal hedge]

but how works this? And an visitor has the name, displayname, birthday, lastSeen (also a date) and a list with a EventInfo, which contains the name and dates of the event. The Event itself has the EventInfo and the List<Visitor> in it but idk how/ when to use one-to-many or many-to-one.

[raven creek]

What do you mean with how does it work?

And I'm a bit unclear what's unclear for you about one to many or many to one.

One book can be read by multiple people, A person can read multiple books. A person has a specific DNA pattern. Etc..

I recommend looking at Squid's link.

[thin crane]

The link isn’t about one to many/many to one though

[raven creek]

My bad, I thought it linked the related articles. https://www.baeldung.com/jpa-hibernate-associations