Question

好吧，我在C＃上工作一点点，现在我开始使用C＃与数据库合作，我已经在几个地方用Google搜索了，我无法确定哪里出错了，无处不在我需要打开一个连接，但它已经打开了。

        SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;Integrated Security=True;AttachDbFilename=C:\Users\Gustavo\Documents\Visual Studio 2013\Projects\hour\hour\Database1.mdf");
        con.Open();
        try
        {
            string query = "INSERT INTO [Table] (name, time) VALUES ('test',1)";
            SqlCommand cmd = new SqlCommand(query);
            cmd.ExecuteNonQuery();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }

Answer 1

使用using，处理关闭和处理，以防您忘记明确地执行此操作。把它放在try中，你在try之外有连接open命令，所以它不会捕获任何连接错误。您可能也希望查看参数化命令。

using (SqlConnection conn = new SqlConnection(@"Data Source=(LocalDB)\v11.0;Integrated Security=True;AttachDbFilename=C:\Users\Gustavo\Documents\Visual Studio 2013\Projects\hour\hour\Database1.mdf"))
{
        conn.Open();
        using (SqlCommand cmd = new SqlCommand("INSERT INTO [Table] (name, time) VALUES (@name,@time)", conn))
        {
            cmd.Parameters.AddWithValue("@name", "test");
            cmd.Parameters.AddWithValue("@time", 1);
            cmd.CommandType = CommandType.Text;
            cmd.ExecuteNonQuery();
        }
}

Answer 2

  SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\v11.0;Integrated Security=True;AttachDbFilename=C:\Users\Gustavo\Documents\Visual Studio 2013\Projects\hour\hour\Database1.mdf");
        try
        {
            string query = "INSERT INTO [Table] (name, time) VALUES ('test',1)";
            SqlCommand cmd = new SqlCommand(query,con);
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.ToString());
        }

Answer 3

您需要将命令分配给连接。例如：

    private static void ReadOrderData(string connectionString)
    {
        string queryString = 
            "SELECT OrderID, CustomerID FROM dbo.Orders;";
        using (SqlConnection connection = new SqlConnection(
                   connectionString))
        {

//----

            SqlCommand command = new SqlCommand(
                queryString, connection);


//----
            connection.Open();
            SqlDataReader reader = command.ExecuteReader();
            try
            {
                while (reader.Read())
                {
                    Console.WriteLine(String.Format("{0}, {1}",
                        reader[0], reader[1]));
                }
            }
            finally
            {
                // Always call Close when done reading.
                reader.Close();
            }
        }
    }

Connection属性的错误尚未初始化

3 个答案: