request.get( 'http://localhost:8081/student/listPage', { params:{ sno: this.student.sno, sname: this.student.sname, phone: this.student.phone} }).then(res=>{ this.students = res.data })为什么会报错Error in beforeCreate hook: "TypeError: Cannot read properties of undefined (reading 'sno')"

这个错误提示表明在组件的 `beforeCreate` 钩子函数中，访问了 `this.student.sno` 属性，但是 `this.student` 对象是 `undefined`，导致读取属性失败。这个问题的原因可能有以下几种： 1. `this.student` 对象没有初始化，或者初始化不完整，例如 `sno` 属性没有赋值，导致访问 `sno` 属性时出现了错误。 2. `this.student` 对象在 `beforeCreate` 钩子函数执行时还没有被创建，因此访问其属性时会出现错误。 3. `this` 上下文对象没有绑定正确，导致无法访问 `this.student` 对象。解决这个问题的方法，可以先在组件的 `created` 钩子函数中对 `this.student` 对象进行初始化，并确保所有属性都有正确的值。另外，也可以将请求数据放到 `mounted` 钩子函数中，这样可以确保组件的数据已经被完全初始化。最后，还需要确保 `this` 上下文对象已经正确绑定。

编写程序,实现对数据库StudentInfo中的表student进行插入操作.要求使用预处理语句对象PreparedStatement完成以下数据的插入: insert into student values('001','张三',18,'女') 注:给定数据库登录用户名:sa,密码:123. Input.jsp: 请输入待新增的学生信息学号: 姓名: 年龄: 性别: addStudent.jsp: <% String url="jdbc:sqlserver://localhost;databaseName=StudentInfo"; request.setCharacterEncoding("utf-8"); String sno = request.getParameter("sno"); String sname = request.getParameter("sname"); int sage = Integer.valueOf(request.getParameter("sage")); String sex = request.getParameter("sex"); try{ //补全此部分代码 } // 捕获异常 catch(SQLException ex) { System.out.println ("\n* 发生SQL异常 *\n"+ex.getMessage()); } catch(ClassNotFoundException ex) { System.out.println(ex); }

addStudent.jsp: ``` <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Add Student</title> </head> <body> <h1>Add Student</h1> <form action="insertStudent.jsp" method="post"> <label for="sno">学号：</label> <input type="text" id="sno" name="sno" /><br> <label for="sname">姓名：</label> <input type="text" id="sname" name="sname" /><br> <label for="sage">年龄：</label> <input type="text" id="sage" name="sage" /><br> <label for="sex">性别：</label> <input type="text" id="sex" name="sex" /><br> <input type="submit" value="提交" /> </form> </body> </html> ``` insertStudent.jsp: ``` <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ page import="java.sql.*" %> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert Student</title> </head> <body> <% String url="jdbc:sqlserver://localhost;databaseName=StudentInfo"; request.setCharacterEncoding("utf-8"); String sno = request.getParameter("sno"); String sname = request.getParameter("sname"); int sage = Integer.valueOf(request.getParameter("sage")); String sex = request.getParameter("sex"); try{ Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); Connection conn = DriverManager.getConnection(url,"sa","123"); String sql = "insert into student values(?,?,?,?)"; PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setString(1, sno); pstmt.setString(2, sname); pstmt.setInt(3, sage); pstmt.setString(4, sex); int num = pstmt.executeUpdate(); if(num > 0){ out.print("插入成功！"); } pstmt.close(); conn.close(); } catch(SQLException ex){ System.out.println ("\n*** 发生SQL异常 ***\n"+ex.getMessage()); } catch(ClassNotFoundException ex){ System.out.println(ex); } %> </body> </html> ```

编写程序，实现对数据库StudentInfo中的表student进行插入操作。要求使用预处理语句对象PreparedStatement完成以下数据的插入： insert into student values('001','张三',18,'女') 注：给定数据库登录用户名：sa，密码：123。 Input.jsp: <body> <form action = "addStudent.jsp" method = "post"> 请输入待新增的学生信息<br> 学号：<input type="text" name="sno"/><br> 姓名：<input type="text" name= "sname"/><br> 年龄：<input type="text" name= "sage"/><br> 性别：<input type="text" name= "sex"/><br> <input type = "submit" value= "新增"/> </form> </body> addStudent.jsp: <body> <% String url="jdbc:sqlserver://localhost;databaseName=StudentInfo"; request.setCharacterEncoding("utf-8"); String sno = request.getParameter("sno"); String sname = request.getParameter("sname"); int sage = Integer.valueOf(request.getParameter("sage")); String sex = request.getParameter("sex"); try{ //补全此部分代码 } // 捕获异常 catch(SQLException ex) { System.out.println ("\n* 发生SQL异常 *\n"+ex.getMessage()); } catch(ClassNotFoundException ex) { System.out.println(ex); }

补全代码如下： ```java <% String url="jdbc:sqlserver://localhost;databaseName=StudentInfo"; request.setCharacterEncoding("utf-8"); String sno = request.getParameter("sno"); String sname = request.getParameter("sname"); int sage = Integer.valueOf(request.getParameter("sage")); String sex = request.getParameter("sex"); try{ Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); Connection conn = DriverManager.getConnection(url,"sa","123"); String sql = "insert into student values(?,?,?,?)"; PreparedStatement pstmt = conn.prepareStatement(sql); pstmt.setString(1, sno); pstmt.setString(2, sname); pstmt.setInt(3, sage); pstmt.setString(4, sex); pstmt.executeUpdate(); out.println("新增成功"); conn.close(); } // 捕获异常 catch(SQLException ex) { System.out.println ("\n*** 发生SQL异常 ***\n"+ex.getMessage()); } catch(ClassNotFoundException ex) { System.out.println(ex); } %> ```

阅读全文

request.get( 'http://localhost:8081/student/listPage', { params:{ sno: this.student.sno, sname: this.student.sname, phone: this.student.phone} }).then(res=>{ this.students = res.data })为什么会报错Error in beforeCreate hook: "TypeError: Cannot read properties of undefined (reading 'sno')"

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