必须在 c# Winforms 中声明一个静态变量

Question

我收到一个错误，您必须声明一个静态变量@campus_id。我不知道如何声明以及在哪里声明以及声明静态变量意味着什么。请帮助我！

private void btnSave_Click(object sender, EventArgs e)
{
    try
    {
        CS = ConfigurationManager
                   .ConnectionStrings["UMSdbConnectionString"].ConnectionString;
        using (SqlConnection con = new SqlConnection(CS))
        {
            con.Open();
            SqlCommand cmd = new SqlCommand(
                "SELECT ISNULL(MAX(campus_id),0)+1 FROM Campus", con);
            cmd.CommandType = CommandType.Text;
            tbCampusID.Text = cmd.ExecuteScalar().ToString();

            using (SqlCommand cmd1 = new SqlCommand(
              "INSERT INTO Campus (campus_id,campus_name)VALUES(@camp_id,camp_name)", con))
            {
                cmd1.CommandType = CommandType.Text;
                cmd1.Parameters.AddWithValue("@campus_id", tbCampusID.Text);
                cmd1.Parameters.AddWithValue("@campus_name", tbCampusName.Text);
                cmd1.ExecuteNonQuery();
                con.Close();
                MessageBox.Show("Record Saved");
            }
        }
    }
    catch (Exception)
    {
    }
}

Answer 1

您的 SQL 查询和对 Parameters.AddWithValue 的调用中的参数名称必须匹配：

using (SqlCommand cmd1 = new SqlCommand(
    "INSERT INTO Campus (campus_id, campus_name) VALUES(@campus_id, @campus_name)", con))
{
    cmd1.CommandType = CommandType.Text;
    cmd1.Parameters.AddWithValue("@campus_id", tbCampusID.Text);
    cmd1.Parameters.AddWithValue("@campus_name", tbCampusName.Text);
    cmd1.ExecuteNonQuery();
    con.Close();
}

Answer 2

您正在为尚未定义的占位符添加值。看到这个声明 cmd1.Parameters.AddWithValue("@campus_id", tbCampusID.Text); 此处您使用 campus_id 作为占位符并查看插入查询，即 INSERT INTO Campus (campus_id,campus_name)VALUES(@camp_id,camp_name)。那里的占位符是 camp_id 并且导致了错误；像这样使用：

string querySql = "INSERT INTO Campus (campus_id, campus_name) VALUES(@camp_id, @campus_name)"
using (SqlCommand cmd1 = new SqlCommand(querySql, con))
{
    cmd1.CommandType = CommandType.Text;
    cmd1.Parameters.AddWithValue("@camp_id", tbCampusID.Text);
    cmd1.Parameters.AddWithValue("@campus_name", tbCampusName.Text);
    cmd1.ExecuteNonQuery();
    con.Close();
}

必须在 c# Winforms 中声明一个静态变量

Must Declare a static variable in c# Winfoms

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