C# - 更新 SQL 表

Question

我想更新我的 sql 表。我在这里搜索并找到了有关如何解决该问题的解决方案。但遗憾的是它只是不会更新数据库。我不知道问题是什么。 我检查了几次 sql 命令写错误，但找不到或修复它们，但遗憾的是仍然没有。我想这是 try 块中的东西，但找不到。

这是我的代码：

string connetionString = null;
SqlConnection connection;
SqlCommand command;
string sql = null;
SqlDataReader dataReader;
connetionString = "Data Source=xxx\\xxx;Initial Catalog=xxx;User ID=xxx;Password=xxx";
sql = "UPDATE Employees SET LastName = '" + Lnamestring + "', FirstName = '" + Fnamestring + "', Title = '" + Titelstring + "', TitleOfCourtesy = '" + ToCstring + "', BirthDate = '" + Birthdatestring + "', HireDate = '" + Hiredatestring + "', Address = '" + Adressstring + "', City = '" + Citystring + "', Region = '" + Regionstring + "', PostalCode = '" + Postalstring + "', Country = '" + Countrystring + "', HomePhone = '" + Phonestring + "', Extension = '" + Extensionsstring + "', Notes = '" + Notesstring + "', ReportsTo = '" + ReportTostring + "' WHERE EmployeeID = '" + IDstring + "'; ";
connection = new SqlConnection(connetionString);
try
{
    connection.Open();
    command = new SqlCommand(sql, connection);
    SqlDataAdapter sqlDataAdap = new SqlDataAdapter(command);

    command.Dispose();
    connection.Close();
    MessageBox.Show("workd ! ");

}
catch (Exception ex)
{
    MessageBox.Show("Can not open connection ! ");
}

我希望有人能帮我找出我的错误。

编辑：当我尝试它时，它似乎可以工作，因为窗口弹出“workd”但数据库没有改变。

Answer 1

正如 Michał Turczyn 在他的 answer 中所写，您的代码存在一些问题。
我同意他写的所有内容，但我认为您可能会从查看代码的外观中受益 - 所以您可以这样做：

var connetionString = "Data Source=EVOPC18\\PMSMART;Initial Catalog=NORTHWND;User ID=test;Password=test";
var sql = "UPDATE Employees SET LastName = @LastName, FirstName = @FirstName, Title = @Title ... ";// repeat for all variables
try
{
    using(var connection = new SqlConnection(connetionString))
    {
        using(var command = new SqlCommand(sql, connection))
        {
            command.Parameters.Add("@LastName", SqlDbType.NVarChar).Value = Lnamestring;
            command.Parameters.Add("@FirstName", SqlDbType.NVarChar).Value = Fnamestring;
            command.Parameters.Add("@Title", SqlDbType.NVarChar).Value = Titelstring;
            // repeat for all variables....
            connection.Open();
            command.ExecuteNonQuery();
        }       
    }
}
catch (Exception e)
{
    MessageBox.Show($"Failed to update. Error message: {e.Message}");
}

Answer 2

您的代码存在一些问题：

1) 在使用IDisposable 对象时使用using，在您的情况下为connection 和command。

2) 出于安全原因，按照 cmets 中的建议，使用 SqlCommandParameters 而不是连接字符串（谷歌“防止 SQL 注入”）

3) 你没有执行你的查询！如果你不这样做，你希望它如何产生影响？例如，SqlCommand 类中有 ExecuteNonQuery 之类的方法。

Answer 3

string connetionString = null;
SqlConnection connection;
SqlCommand command;
string sql = null;
SqlDataReader dataReader;
connetionString = "Data Source=EVOPC18\\PMSMART;Initial Catalog=NORTHWND;User ID=test;Password=test";
sql = "UPDATE Employees SET LastName = '" + Lnamestring + "', FirstName = '" + Fnamestring + "', Title = '" + Titelstring + "', TitleOfCourtesy = '" + ToCstring + "', BirthDate = '" + Birthdatestring + "', HireDate = '" + Hiredatestring + "', Address = '" + Adressstring + "', City = '" + Citystring + "', Region = '" + Regionstring + "', PostalCode = '" + Postalstring + "', Country = '" + Countrystring + "', HomePhone = '" + Phonestring + "', Extension = '" + Extensionsstring + "', Notes = '" + Notesstring + "', ReportsTo = '" + ReportTostring + "' WHERE EmployeeID = '" + IDstring + "'; ";
connection = new SqlConnection(connetionString);
try
{
    connection.Open();
    command = new SqlCommand(sql, connection);
    SqlDataAdapter sqlDataAdap = new SqlDataAdapter(command);

    command.ExecuteNonQuery();

    command.Dispose();
    connection.Close();
    MessageBox.Show("workd ! ");

}
catch (Exception ex)
{
    MessageBox.Show("Can not open connection ! ");
}

1. 别忘了执行命令
2. 尽量从Exception获取堆栈跟踪或错误消息。例如：MessageBox.Show($"Can not open connection ! {e.GetBaseException().Message}, {e.StackTrace}");

Answer 4

请使用ExecuteNonQuery() 而不是SqlDataAdapter：

connection.Open();
command = new SqlCommand(sql, connection);
command.ExecuteNonQuery();
command.Dispose();
connection.Close();
MessageBox.Show("workd ! ");