Added Author and book entities

src/main/java/guru/springframework/spring6webapp/domain/Author.java

@@ -0,0 +1,50 @@
+package guru.springframework.spring6webapp.domain;
+
+import jakarta.persistence.*;
+
+import java.util.Set;
+
+public class Author {
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private int id;
+    private String firstName;
+
+    private String lastName;
+
+    @ManyToMany
+    @JoinTable(name = "authors")
+    private Set<Book> books;
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getFirstName() {
+        return firstName;
+    }
+
+    public void setFirstName(String firstName) {
+        this.firstName = firstName;
+    }
+
+    public String getLastName() {
+        return lastName;
+    }
+
+    public void setLastName(String lastName) {
+        this.lastName = lastName;
+    }
+
+    public Set<Book> getBooks() {
+        return books;
+    }
+
+    public void setBooks(Set<Book> books) {
+        this.books = books;
+    }
+}

src/main/java/guru/springframework/spring6webapp/domain/Book.java

@@ -0,0 +1,53 @@
+package guru.springframework.spring6webapp.domain;
+
+import jakarta.persistence.*;
+
+import java.util.Set;
+
+@Entity
+public class Book {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.AUTO)
+    private int id;
+    private String title;
+
+    private String isbn;
+
+    @ManyToMany
+    @JoinTable(name = "author_book", joinColumns = @JoinColumn(name = "book_id"),
+            inverseJoinColumns = @JoinColumn(name = "author_id"))
+    private Set<Author> authors;
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String isbn) {
+        this.isbn = isbn;
+    }
+
+    public Set<Author> getAuthors() {
+        return authors;
+    }
+
+    public void setAuthors(Set<Author> authors) {
+        this.authors = authors;
+    }
+}