网上图书商城项目学习笔记-030删除二级分类

一、流程分析

二、代码

1.view层

和一相同

 

2.servlet层

(1)AdminCategoryServlet.java

    /**
     * 删除二级分类
     * @param req
     * @param resp
     * @return
     * @throws ServletException
     * @throws IOException
     */
    public String deleteChild(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String cid = req.getParameter("cid");
        int count = bookService.findBookCountByCategory(cid);
        if(count > 0) {
            req.setAttribute("code", "eror");
            req.setAttribute("msg", "该分类下还有图书，不能删除！");
            return "/adminjsps/msg.jsp";
        }
        service.delete(cid);
        return findAll(req, resp);
    }

3.service层

(1)AdminCategory.java

    /**
     * 删除分类
     * @param cid
     */
    public void delete(String cid) {
        try {
            categoryDao.delete(cid);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

(2)BookService.java 

    /**
     * 查询某分类下的图书数量
     * @param cid
     * @return
     */
    public int findBookCountByCategory(String cid) {
        try {
            return bookDao.findBookCountByCategory(cid);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

4.dao层

(1)AdminCategoryDao.java

    /**
     * 删除分类
     * @param cid
     * @throws SQLException
     */
    public void delete(String cid) throws SQLException {
        String sql = "delete from t_category where cid=?";
        qr.update(sql, cid);
    }

(2)BookDao

    /**
     * 查询某分类下的图书数量
     * @param cid
     * @return
     * @throws SQLException 
     */
    public int findBookCountByCategory(String cid) throws SQLException {
        String sql = "select count(*) from t_book where cid=?";
        Number count = (Number) qr.query(sql, new ScalarHandler(), cid);
        return count == null ? 0 : count.intValue();
    }