借书功能的实现思路

v0: 能正常实现借书的操作

    /**
     * 借书
     * @param bookDTO
     * @return
     */
    @Override
    @Transactional

    public boolean borrow(BookDTO bookDTO) {
        Book book = bookMapper.getBookById(bookDTO.getBookId());
        if (book.getNumber()-book.getStatus() > 0){
            if (book.getNumber()-book.getStatus() >= bookDTO.getNumber()){
                bookMapper.addStatus(bookDTO);
                BookUser history = bookMapper.getHistory(bookDTO);
                if (history != null){
                    bookDTO.setId(history.getId());
                    bookMapper.borrowHistory(bookDTO);
                }else{
                    bookMapper.saveHistory(bookDTO);
                }
                return true;
            }else{
                return false;
            }
        }
        return false;
    }

V1: 悲观锁

获取图书信息时,使用了新的mapper层的获取图书信息方法:

    /**
     * 用于借书操作并锁定记录的方法
     * @param id
     */
    @Select("SELECT * FROM book WHERE id = #{id} FOR UPDATE")
    Book getBookForBorrow(int id);

V2: 乐观锁

给book表新加了version字段,并在实体类的version字段添加@Version注解,修改了判断条件和更新方法

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class BookDTO {
    private Integer id;
    private Integer userId;
    private Integer bookId;
    private int status;
    private int number;
    private long version;
}



@Data
@AllArgsConstructor
@NoArgsConstructor
public class Book {
    private Integer id;
    private Integer uuid;
    private String name;
    private String category;
    private int status;
    private int number;
    private String author;
    private String publisher;
    private String img;
    private double price;
    @TableField(fill = FieldFill.INSERT)//插入时填充字段
    private LocalDateTime createdTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)//插入和更新时填充字段
    private LocalDateTime updatedTime;
    @Version
    private long version;
}



    /**
     * 借书
     * @param bookDTO
     * @return
     */
    @Override
    @Transactional
    public boolean borrow(BookDTO bookDTO) {
        // 悲观锁
//        Book book = bookMapper.getBookForBorrow(bookDTO.getBookId());
        Book book = bookMapper.getBookById(bookDTO.getBookId());
        if (book == null){
            return false;
        }
        if (book.getNumber()-book.getStatus() > 0){
            // 检查版本号是否一致，如果一致则准备更新
            if (book.getVersion() == bookDTO.getVersion()) {
                if (book.getNumber()-book.getStatus() >= bookDTO.getNumber()){
                    // 对图书表的操作
                    bookMapper.updateStatusAndVersion(bookDTO);
                    // 对借书记录表的操作
                    BookUser history = bookMapper.getHistory(bookDTO);
                    if (history != null){
                        bookDTO.setId(history.getId());
                        bookMapper.borrowHistory(bookDTO);
                    }else{
                        bookMapper.saveHistory(bookDTO);
                    }
                    return true;
                }else{
                    return false;
                }
            } else {
                // 版本号不一致，表示数据已经被其他事务修改，需要抛出异常或返回错误信息
                throw new OptimisticLockingFailureException("图书数据已被其他事务修改，请稍后重试");
            }
        }
        return false;
    }



    /**
     * 增加图书的借书数量
     * @param bookDTO
     */
    @Update("UPDATE book SET status = book.status + #{number}, version = version + 1 WHERE id = #{bookId}")
    void updateStatusAndVersion(BookDTO bookDTO);