在 razor 页面中使用 ADO.NET 从数据库中获取数据

Question

当我尝试在 URL 中搜索不存在的员工时，该 URL 会返回肯定响应，就好像它在数据库中不存在的 id 之后找到员工一样，但它是空的而不是将我重定向到NotFound 页面。下面是从数据库中检索数据的代码：

public Employee GetEmployeeData(int? id)
    {
        Employee employee = new Employee();
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            string sqlQuery = "SELECT * FROM tblEmployee WHERE EmployeeID= " + id;
            SqlCommand commend = new SqlCommand(sqlQuery, connection);

            connection.Open();
            SqlDataReader readData = commend.ExecuteReader();

            while (readData.Read())
            {
                employee.Id = Convert.ToInt32(readData["EmployeeID"]);
                employee.Name = readData["Name"].ToString();
                employee.Gender = readData["Gender"].ToString();
                employee.Department = readData["Department"].ToString();
                employee.City = readData["City"].ToString();
            }
        }
        return employee;
    }

这是我的EditEmployee.cshmtl.cs 中的OnGet 和OnPost 方法：

 public ActionResult OnGet(int? id)
    {
        if (id == null)
        {
            return RedirectToPage("/NotFound");
        }
        Employee = objemployee.GetEmployeeData(id);

        if (Employee == null)
        {
            return RedirectToPage("/NotFound");
        }
        return Page();
    }
    public ActionResult OnPost()
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }
        objemployee.UpdateEmployee(Employee);

        return RedirectToPage("./EmployeeIndex");
    }

当我转到编辑页面并尝试更改 URL 中的id 时，任何int 的答案都不是空的，而是空的。这是我制作教程的链接enter link description here

这是图片，这是我的问题。我在 URL 中写了一个在我的数据库中不存在的 id，但它仍然返回一个 null 和空 id。 [2]：https://i.stack.imgur.com/HC9yx.png

请给点想法好吗？

Answer 1

您应该在获取数据失败时返回 null，而不是始终返回 Employee 的新实例。 尝试以下代码更改

    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        string sqlQuery = "SELECT * FROM tblEmployee WHERE EmployeeID= " + id;
        SqlCommand commend = new SqlCommand(sqlQuery, connection);
    
        connection.Open();
        SqlDataReader readData = commend.ExecuteReader();
        
        if(!readData.HasRows) return null;
    
        Employee employee = new Employee();
    
        while (readData.Read())
        {
            employee.Id = Convert.ToInt32(readData["EmployeeID"]);
            employee.Name = readData["Name"].ToString();
            employee.Gender = readData["Gender"].ToString();
            employee.Department = readData["Department"].ToString();
            employee.City = readData["City"].ToString();
        }
        return employee;
    }