Initializing Data wih Spring

src/main/java/guru/springframework/spring5webapp/bootstrap/BootStrapData.java

@@ -0,0 +1,43 @@
+package guru.springframework.spring5webapp.bootstrap;
+
+import guru.springframework.spring5webapp.domain.Author;
+import guru.springframework.spring5webapp.domain.Book;
+import guru.springframework.spring5webapp.repositories.AuthorRepository;
+import guru.springframework.spring5webapp.repositories.BookRepository;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.stereotype.Component;
+
+@Component
+public class BootStrapData implements CommandLineRunner {
+
+    private final AuthorRepository authorRepository;
+    private final BookRepository bookRepository;
+
+    public BootStrapData(AuthorRepository authorRepository, BookRepository bookRepository) {
+        this.authorRepository = authorRepository;
+        this.bookRepository = bookRepository;
+    }
+
+    @Override
+    public void run(String... args) throws Exception {
+
+        Author eric = new Author("Eric", "Evans");
+        Book ddd = new Book("Domain Driven Design", "123123");
+        eric.getBooks().add(ddd);
+        ddd.getAuthors().add(eric);
+
+        authorRepository.save(eric);
+        bookRepository.save(ddd);
+
+        Author rod = new Author("Rod", "Johnson");
+        Book noEJB = new Book("J2EE Development without EJB", "4423241241");
+        rod.getBooks().add(noEJB);
+        noEJB.getAuthors().add(rod);
+
+        authorRepository.save(rod);
+        bookRepository.save(noEJB);
+
+        System.out.println("Started in Bootstrap");
+        System.out.println("Number of Books: " + bookRepository.count());
+    }
+}

src/main/java/guru/springframework/spring5webapp/domain/Author.java

@@ -1,6 +1,7 @@
 package guru.springframework.spring5webapp.domain;
 
 import javax.persistence.*;
+import java.util.HashSet;
 import java.util.Objects;
 import java.util.Set;
 
@@ -12,15 +13,14 @@ public class Author {
     private String firstName;
     private String lastName;
     @ManyToMany(mappedBy = "authors")
-    private Set<Book> books;
+    private Set<Book> books = new HashSet<>();
 
     public Author(){
     }
 
-    public Author(String firstName, String lastName, Set<Book> books) {
+    public Author(String firstName, String lastName) {
         this.firstName = firstName;
         this.lastName = lastName;
-        this.books = books;
     }
 
     public Long getId() {

src/main/java/guru/springframework/spring5webapp/domain/Book.java

@@ -1,6 +1,7 @@
 package guru.springframework.spring5webapp.domain;
 
 import javax.persistence.*;
+import java.util.HashSet;
 import java.util.Objects;
 import java.util.Set;
 @Entity
@@ -14,15 +15,14 @@ public class Book {
     @ManyToMany
     @JoinTable(name = "author_book", joinColumns = @JoinColumn(name = "book_id"),
                 inverseJoinColumns = @JoinColumn(name = "author_id"))
-    private Set<Author> authors;
+    private Set<Author> authors = new HashSet<>();
 
     public Book() {
     }
 
-    public Book(String title, String isbn, Set<Author> authors) {
+    public Book(String title, String isbn) {
         this.title = title;
         this.isbn = isbn;
-        this.authors = authors;
     }
 
     public Long getId() {