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document that records can now be used as @IdClasses and @EmbeddableIds 

Signed-off-by: Gavin King <gavin@hibernate.org>
This commit is contained in:
Gavin King 2024-04-27 01:00:20 +02:00
parent 647f689d1b
commit a869ce1c1e
1 changed files with 5 additions and 51 deletions
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56
documentation/src/main/asciidoc/introduction/Entities.adoc
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@ -364,42 +364,15 @@ class Book {
But this approach comes with a problem: what object can we use to identify a `Book` and pass to methods like `find()` which accept an identifier?
The solution is to write a separate class with fields that match the identifier attributes of the entity.
The `@IdClass` annotation of the `Book` entity identifies the id class to use for that entity:
Every such id class must override `equals()` and `hashCode()`.
Of course, the easiest way to satisfy these requirements is to declare the id class as a `record`.
[source,java]
----
class BookId {
String isbn;
int printing;
BookId() {}
BookId(String isbn, int printing) {
this.isbn = isbn;
this.printing = printing;
}
@Override
public boolean equals(Object other) {
if (other instanceof BookId) {
BookId bookId = (BookId) other;
return bookId.isbn.equals(isbn)
&& bookId.printing == printing;
}
else {
return false;
}
}
@Override
public int hashCode() {
return isbn.hashCode();
}
}
record BookId(String isbn, int printing) {}
----
Every id class should override `equals()` and `hashCode()`.
The `@IdClass` annotation of the `Book` entity identifies `BookId` as the id class to use for that entity.
This is not our preferred approach.
Instead, we recommend that the `BookId` class be declared as an `@Embeddable` type:
@ -407,21 +380,7 @@ Instead, we recommend that the `BookId` class be declared as an `@Embeddable` ty
[source,java]
----
@Embeddable
class BookId {
String isbn;
int printing;
BookId() {}
BookId(String isbn, int printing) {
this.isbn = isbn;
this.printing = printing;
}
...
}
record BookId(String isbn, int printing) {}
----
We'll learn more about <<embeddable-objects>> below.
@ -881,11 +840,6 @@ record Name(String firstName, String middleName, String lastName) {}
In this case, the requirement for a constructor with no parameters is relaxed.
[NOTE]
====
Unfortunately, as of May 2023, Java `record` types still cannot be used as ``@EmbeddedId``s.
====
We may now use our `Name` class (or record) as the type of an entity attribute:
[source,java]