第三章练习答案

练习 1：JPA 关系映射

@Entity
@Table(name = "authors")
public class Author {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Book> books = new ArrayList<>();
    
    public void addBook(Book book) {
        books.add(book);
        book.setAuthor(this);
    }
    
    public void removeBook(Book book) {
        books.remove(book);
        book.setAuthor(null);
    }
}

@Entity
@Table(name = "books")
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String title;
    
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "author_id")
    private Author author;
    
    @ManyToMany
    @JoinTable(
        name = "book_category",
        joinColumns = @JoinColumn(name = "book_id"),
        inverseJoinColumns = @JoinColumn(name = "category_id")
    )
    private Set<Category> categories = new HashSet<>();
}

@Entity
@Table(name = "categories")
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    private String name;
    
    @ManyToMany(mappedBy = "categories")
    private Set<Book> books = new HashSet<>();
}

练习 2：自定义查询

public interface BookRepository extends JpaRepository<Book, Long> {
    
    List<Book> findByTitleContainingIgnoreCase(String title);
    
    List<Book> findByAuthor_Name(String authorName);
    
    @Query("SELECT b FROM Book b WHERE b.author.id = :authorId")
    List<Book> findBooksByAuthorId(@Param("authorId") Long authorId);
    
    @Query(value = "SELECT * FROM books WHERE YEAR(published_date) = :year", nativeQuery = true)
    List<Book> findBooksByPublishedYear(@Param("year") int year);
    
    @Modifying
    @Query("UPDATE Book b SET b.title = :title WHERE b.id = :id")
    int updateBookTitle(@Param("id") Long id, @Param("title") String title);
}

练习 3：Spring Security 基础

@Configuration
@EnableWebSecurity
public class SecurityConfig {
    
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
            .csrf().disable()
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/api/public/**").permitAll()
                .requestMatchers("/api/admin/**").hasRole("ADMIN")
                .anyRequest().authenticated()
            )
            .httpBasic();
        
        return http.build();
    }
    
    @Bean
    public UserDetailsService userDetailsService() {
        UserDetails user = User.builder()
            .username("user")
            .password(passwordEncoder().encode("password"))
            .roles("USER")
            .build();
        
        UserDetails admin = User.builder()
            .username("admin")
            .password(passwordEncoder().encode("admin"))
            .roles("ADMIN")
            .build();
        
        return new InMemoryUserDetailsManager(user, admin);
    }
    
    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    }
}

返回第三章概览