演示四：用 MyBatis-Plus 把图书检索接到数据库

# ① 驱动类名
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

# ② 连接地址（注意 serverTimezone 和 useSSL 这两个参数）
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/book_db?useUnicode=true&characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai&allowPublicKeyRetrieval=true

# ③ 账号
spring.datasource.username=root

# ④ 密码（改成你自己的）
spring.datasource.password=123456

mybatis-plus.configuration.map-underscore-to-camel-case=true
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;

@TableName("book")
public class Book {

    @TableId(type = IdType.AUTO)
    private Integer id;

    private String name;
    private String author;
    private String press;
    private Integer status;

    public Book() { }

    public Book(Integer id, String name, String author, String press, Integer status) {
        ...
    }
}

import org.mybatis.spring.annotation.MapperScan;

@SpringBootApplication
@MapperScan("com.dashuju.teacher.mapper")
public class TeacherApplication {
    public static void main(String[] args) {
        SpringApplication.run(TeacherApplication.class, args);
    }
}

public List<Book> listAll() {
    return list(new LambdaQueryWrapper<Book>().orderByAsc(Book::getId));
}

public List<Book> search(String name, String author) {
    LambdaQueryWrapper<Book> qw = new LambdaQueryWrapper<>();

    boolean hasName = StringUtils.hasText(name);
    boolean hasAuthor = StringUtils.hasText(author);

    if (hasName || hasAuthor) {
        qw.and(w -> {                        // ← 括号由此而来
            if (hasName) {
                w.like(Book::getName, name);
            }
            if (hasAuthor) {
                if (hasName) {
                    w.or();                  // ← OR 由此而来
                }
                w.like(Book::getAuthor, author);
            }
        });
    }

    qw.orderByAsc(Book::getId);
    return list(qw);
}

import com.dashuju.teacher.service.BookService;
import org.springframework.beans.factory.annotation.Autowired;

@Controller
@RequestMapping("book")
public class BookController {

    @Autowired
    private BookService bookService;

    @RequestMapping("list")
    public String findBook(Model model, HttpSession session) {
        session.setAttribute("user", new User("zhangsan", "ADMIN"));
        model.addAttribute("books", bookService.listAll());
        return "books";
    }

    @RequestMapping("search")
    public String searchBook(Book book, Model model, HttpSession session) {
        session.setAttribute("user", new User("zhangsan", "ADMIN"));
        model.addAttribute("books", bookService.search(book.getName(), book.getAuthor()));
        return "books";
    }
}

public boolean borrow(Integer id) {
    Book book = getById(id);
    if (book == null) {
        return false;                       // 书不存在
    }
    if (book.getStatus() == null || book.getStatus() != 0) {
        return false;                       // 1=借阅中 2=归还中，都不许再借
    }
    book.setStatus(1);
    return updateById(book);                // UPDATE book SET ... WHERE id = ?
}

@RequestMapping("find/{id}")
public String findBook(@PathVariable("id") Integer id) {
    boolean ok = bookService.borrow(id);
    System.out.println("申请借阅图书的id：" + id + " → "
            + (ok ? "借阅成功" : "借阅失败（已借出或不存在）"));
    return "redirect:/book/list";
}

<script>
    function findBookById(id) {
        location.href = '/book/find/' + id;
    }
</script>