【发布时间】：2020-03-12 17:55:26
【问题描述】：
我在表格中有一个按钮，调用插入语句，
private void bttnEnroll_Click(object sender, RoutedEventArgs e)
{
string className;
string section;
SqlConnection sqlCon = new SqlConnection(@"Data Source=DESKTOP-7S08N90;Initial Catalog=UniversityDB;Integrated Security=True");
try
{
DataRowView row = (DataRowView)((Button)e.Source).DataContext;
className = row[0].ToString();
section = row[1].ToString();
if (sqlCon.State == ConnectionState.Closed)
sqlCon.Open();
//SQL query
String query = "INSERT INTO Takes (studentID, className, section, semester, year, time, grade) " +
"SELECT @studentID, className, section, @semester, @year, time, @grade " +
"FROM Section " +
"WHERE className=@className " +
"AND section=@section";
SqlCommand sqlCmd = new SqlCommand(query, sqlCon);
sqlCmd.Parameters.AddWithValue("@studentID", this.studentID);
sqlCmd.Parameters.AddWithValue("@className", className);
sqlCmd.Parameters.AddWithValue("@section", section);
sqlCmd.Parameters.AddWithValue("@semester", this.semester);
sqlCmd.Parameters.AddWithValue("@year", this.year);
sqlCmd.Parameters.AddWithValue("@grade", "N/A");
int rowsAffected = sqlCmd.ExecuteNonQuery();
if (rowsAffected == 1)
{
MessageBox.Show("Class enrolled.");
}
else if (rowsAffected > 1)
{
MessageBox.Show("More than 1 row affected");
} else
{
MessageBox.Show("Class not enrolled.");
}
sqlCmd.Dispose();
}
catch (Exception ex) //if SQL server connection fails
{
MessageBox.Show(ex.Message.ToString() + ". Class failed to enroll.");
}
finally
{
sqlCon.Close();
}
}
最初我以为我可能在某处执行了两次该语句，但我在
上设置了一个断点int rowsAffected = sqlCmd.ExecuteNonQuery();
它返回 2。检查数据库显示插入了 2 行重复数据，而我只想要 1。
完整代码：
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
namespace UniversityDBInterface
{
/// <summary>
/// Interaction logic for Results.xaml
/// </summary>
public partial class Results : Window
{
int studentID;
string semester;
string year;
int deptID;
int courseNum;
string comparison;
Boolean days;
Boolean open;
public Results(String semester, String year, int deptID, int courseNum, String comparison,
Boolean days, Boolean open, int studentID)
{
//init
InitializeComponent();
this.studentID = studentID;
this.semester = semester;
this.year = year; //TODO: ? not sure if this is necessary in our implementation
this.deptID = deptID; //TODO
this.courseNum = courseNum; //TODO
this.comparison = comparison; //TODO
this.days = days; //TODO
this.open = open; //TODO
//SQL
ResultsList();
}
private void ResultsList()
{
SqlConnection sqlCon = new SqlConnection(@"Data Source=DESKTOP-7S08N90;Initial Catalog=UniversityDB;Integrated Security=True");
try
{
if (sqlCon.State == ConnectionState.Closed)
sqlCon.Open();
//SQL query
String query = "SELECT className AS [Class Name], section AS Section, room AS Room " +
"FROM Section " +
"WHERE semester=@Semester ";
SqlCommand sqlCmd = new SqlCommand(query, sqlCon);
sqlCmd.Parameters.AddWithValue("@Semester", this.semester);
//sqlCmd.Parameters.AddWithValue("@Year", this.year);
//Execute command and fill table with data
SqlDataAdapter adapter = new SqlDataAdapter(sqlCmd);
SqlCommandBuilder builder = new SqlCommandBuilder(adapter);
DataTable table = new DataTable();
adapter.Fill(table);
ResultsDataGrid.ItemsSource = table.DefaultView;
ResultsDataGrid.AutoGenerateColumns = true;
ResultsDataGrid.CanUserAddRows = false;
ResultsDataGrid.CanUserSortColumns = true;
sqlCmd.Dispose();
}
catch (Exception ex) //if SQL server connection fails
{
MessageBox.Show(ex.Message);
}
finally
{
sqlCon.Close();
}
}
private void bttnLogout_Click(object sender, RoutedEventArgs e)
{
Login login = new Login();
login.Show();
this.Close();
}
private void bttnBack_Click(object sender, RoutedEventArgs e)
{
MainWindow mainWindow = new MainWindow(studentID, semester, year);
mainWindow.Show();
this.Close();
}
private void preqCheck(SqlConnection con)
{
//TODO
}
private void bttnEnroll_Click(object sender, RoutedEventArgs e)
{
string className;
string section;
SqlConnection sqlCon = new SqlConnection(@"Data Source=DESKTOP-7S08N90;Initial Catalog=UniversityDB;Integrated Security=True");
try
{
DataRowView row = (DataRowView)((Button)e.Source).DataContext;
className = row[0].ToString();
section = row[1].ToString();
if (sqlCon.State == ConnectionState.Closed)
sqlCon.Open();
preqCheck(sqlCon);
//SQL query
String query = "INSERT INTO Takes (studentID, className, section, semester, year, time, grade) " +
"SELECT @studentID, className, section, @semester, @year, time, @grade " +
"FROM Section " +
"WHERE className=@className " +
"AND section=@section";
SqlCommand sqlCmd = new SqlCommand(query, sqlCon);
sqlCmd.Parameters.AddWithValue("@studentID", this.studentID);
sqlCmd.Parameters.AddWithValue("@className", className);
sqlCmd.Parameters.AddWithValue("@section", section);
sqlCmd.Parameters.AddWithValue("@semester", this.semester);
sqlCmd.Parameters.AddWithValue("@year", this.year);
sqlCmd.Parameters.AddWithValue("@grade", "N/A");
int rowsAffected = sqlCmd.ExecuteNonQuery();
if (rowsAffected == 1)
{
MessageBox.Show("Class enrolled.");
}
else if (rowsAffected > 1)
{
MessageBox.Show("More than 1 row affected");
} else
{
MessageBox.Show("Class not enrolled.");
}
sqlCmd.Dispose();
}
catch (Exception ex) //if SQL server connection fails
{
MessageBox.Show(ex.Message.ToString() + ". Class failed to enroll.");
}
finally
{
sqlCon.Close();
}
}
}
}
【问题讨论】：
-
看起来您插入的 select 语句正在抓取两行。尝试修复它，而不是插入。你可以通过
SELECT TOP 1破解这个（不推荐）。另外，不要使用AddWithValue。 -
两个具有基本相同布局的表格是一个糟糕的设计，因为您需要的只是另一列来表明......无论有什么区别（如果他们接受了？哪一年？）。它完全不需要这样的代码
-
@Zer0 啊，是的。谢谢。我认为 className 和 section 是唯一的，但事实证明并非如此。赞赏
-
@ŇɏssaPøngjǣrdenlarp，我知道，表格仍在整理中，但需要进行演示，所以我必须使用我所拥有的。我一定会在小组中提出来。
-
看来你已经知道你的问题是什么了。问题是类名和部分可能不是唯一的。如果可能，您可以做出一个答案并将其标记为答案，以便其他人可以看到它。
标签： c# sql visual-studio