第八天

学习目的
    

学会SQL中的占位符用法

在鲸鱼这几天忙死了，好几天没写了，真对不起各位。这几天让XHTML闹得不开心，虽然以前也知道这个，但没太在意。可现在我是如梦初醒，我发觉XHTML是个信号，所以这几天不得不仔细研究一下这个。很笨，我还没发觉XHTML的奥妙。确实如此，没上过台面，真不知这桌菜怎样好吃。少说了，回到正题。

先把以前的Command的CommandText重新写过：
cmd.CommandText = "INSERT INTO NewsArticle (Title, SubTitle, Writer, Content)"
                            + " valueS ( @Title, @SubTitle, @Writer, @Content )";
这样代码是否很清晰了，我们可以避免一大串的难以看懂的的语句了。

接下来，我们就给这些定位符赋予属性和值了：
cmd.Parameters.Add("@Title", SqlDbType.NVarChar, 50);
cmd.Parameters.Add("@SubTitle", SqlDbType.NVarChar, 50);
cmd.Parameters.Add("@Writer", SqlDbType.NVarChar, 10);
cmd.Parameters.Add("@Content", SqlDbType.NText);

以上我们给每个占位符定义一个值类型，相信不难看懂吧。接者再给于值：
cmd.Parameters["@Title"].value = txtTitle.Text.Trim();
if (txtSubTitle.Text == string.Empty || txtSubTitle.Text.Trim() == "")
{
    cmd.Parameters["@SubTitle"].value = DBNull.value;
}
else
{
    cmd.Parameters["@SubTitle"].value = txtSubTitle.Text.Trim();
}
if (txtWriter.Text == string.Empty || txtWriter.Text.Trim() == "")
{
    cmd.Parameters["@Writer"].value = DBNull.value;
}
else
{
    cmd.Parameters["@Writer"].value = txtWriter.Text;
}
cmd.Parameters["@Content"].value = txtContent.Text;

其实，也可以这样写：
cmd.Parameters.Add("@Title", SqlDbType.NVarChar, 50) .value = txtTitle.Text.Trim();
这要看你喜欢了。

不错吧，程序是否很有条理。

程序代码：
        private void btnPublish_ServerClick(object sender, System.EventArgs e)
        {
            string strConnection = ConfigurationSettings.AppSettings["SqlDatabase1"];

            // 连接SqlServer数据库
            SqlConnection conn = new SqlConnection(strConnection);
            // 建立SqlCommand
            SqlCommand cmd = conn.CreateCommand();
            cmd.CommandText = "INSERT INTO NewsArticle (Title, SubTitle, Writer, Content)"
                                            + " valueS ( @Title, @SubTitle, @Writer, @Content )";
            conn.Open();

            cmd.Parameters.Add("@Title", SqlDbType.NVarChar, 50);
            cmd.Parameters.Add("@SubTitle", SqlDbType.NVarChar, 50);
            cmd.Parameters.Add("@Writer", SqlDbType.NVarChar, 10);
            cmd.Parameters.Add("@Content", SqlDbType.NText);

            cmd.Parameters["@Title"].value = txtTitle.Text.Trim();
            if (txtSubTitle.Text == string.Empty || txtSubTitle.Text.Trim() == "")
            {
                cmd.Parameters["@SubTitle"].value = DBNull.value;
            }
            else
            {
                cmd.Parameters["@SubTitle"].value = txtSubTitle.Text.Trim();
            }
            if (txtWriter.Text == string.Empty || txtWriter.Text.Trim() == "")
            {
                cmd.Parameters["@Writer"].value = DBNull.value;
            }
            else
            {
                cmd.Parameters["@Writer"].value = txtWriter.Text;
            }
            cmd.Parameters["@Content"].value = txtContent.Text;
            // 插入记录
            try
            {
                cmd.ExecuteNonQuery();
            }
            catch (Exception ex)
            {
                Response.Write("<script language=javascript>alert('输入错误，数据库不能更新。')</script>");
            }
            finally
            {
                conn.Close();
            }
        }