REST API: Generate book hash when adding a new book with curl POST

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/java/com/fjordtek/bookstore/model/BookEventHandler.java

@@ -0,0 +1,38 @@
+//Pekka Helenius <fincer89@hotmail.com>, Fjordtek 2020
+
+package com.fjordtek.bookstore.model;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.rest.core.annotation.HandleAfterCreate;
+import org.springframework.data.rest.core.annotation.RepositoryEventHandler;
+import org.springframework.stereotype.Component;
+
+/*
+ * When using REST API to add a new book, we need to add a corresponding
+ * book hash Id to BOOK_HASH table, as well.
+ *
+ * For instance, this is a case with the following alike curl commands:
+ *     curl --request POST --header "Content-Type: application/json" --data
+ *     '{"title":"Bloody Chamber", ...}' http://localhost:8080/api/booklist
+ *
+ * Ref: https://docs.spring.io/spring-data/rest/docs/current/reference/html/#events
+ *      https://stackoverflow.com/questions/49504103/override-spring-data-rest-post-method
+ *      https://www.baeldung.com/spring-data-rest-events
+ */
+
+@Component
+@RepositoryEventHandler(Book.class)
+public class BookEventHandler {
+
+	@Autowired
+	private BookHashRepository bookHashRepository;
+
+	@HandleAfterCreate
+	public void handleAfterCreate(Book book) {
+		BookHash bookHash = new BookHash();
+		book.setBookHash(bookHash);
+		bookHash.setBook(book);
+
+		bookHashRepository.save(bookHash);
+	}
+}