100165629.htm
来自「C#高级编程(第三版),顶死你们。。 。up」· HTM 代码 · 共 151 行 · 第 1/2 页
HTM
151 行
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">this.sqlInsertCommand2.Paramaters.Add(</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> new System.Data.SqlClient.SqlParamater("@CustomerID",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> System.Data.SqlDbType.NVarChar, 5, "CustomerID"));</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">// Other Paramaters omitted for clarity</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">//</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">// sqlUpdateCommand1</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">// </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">this.sqlUpdateCommand2.CommandText = @"UPDATE Customers</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> SET CustomerID = @CustomerID, CompanyName = @CompanyName, </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> ContactName = @ContactName, ContactTitle = @ContactTitle, </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Address = @Address, City = @City, Region = @Region, </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> PostalCode = @PostalCode, Country = @Country, </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Phone = @Phone, Fax = @Fax</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> WHERE (CustomerID = @Original_CustomerID)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (Address = @Original_Address OR @Original_Address IS NULL</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 117.35pt"><span lang="EN-US">AND Address IS NULL ) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 83.95pt"><span lang="EN-US">AND (City = @Original_City OR @Original_City IS NULL AND City IS NULL)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (CompanyName = @Original_CompanyName) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (ContactName = @Original_ContactName OR @Original_ContactName IS NULL</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 117.35pt"><span lang="EN-US"> AND ContactName IS NULL ) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (ContactTitle = @Original_ContactTitle OR @Original_ContactTitle IS NULL</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 117.35pt"><span lang="EN-US"> AND ContactTitle IS NULL ) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (Country = @Original_Country OR @Original_Country IS NULL</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 122.15pt"><span lang="EN-US">AND Country IS NULL ) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (Fax = @Original_Fax OR @Original_Fax IS NULL AND Fax IS NULL) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (Phone = @Original_Phone OR @Original_Phone IS NULL AND Phone IS NULL) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (PostalCode = @Original_PostalCode OR @Original_PostalCode IS NULL</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 122.15pt"><span lang="EN-US">AND PostalCode IS NULL ) </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> AND (Region = @Original_Region OR @Original_Region IS NULL</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 122.15pt"><span lang="EN-US">AND Region IS NULL );</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> SELECT CustomerID, CompanyName, ContactName, ContactTitle, </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Address, City, Region, PostalCode, Country, Phone, Fax</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> FROM Customers</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> WHERE (CustomerID = @ CustomerID)";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">this.sqlUpdateCommand2.Connection = this.sqlConnection1;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US">this.sqlUpdateCommand2.Paramaters.Add(</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> new System.Data.SqlClient.SqlParamater("@CustomerID",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> System.Data.SqlDbType.NVarChar, 5, "CustomerID"));</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">// Other Paramaters omitted for clarity</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">这些命令中的主要部分是已经生成的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">。对于</span><span lang="EN-US">INSERT</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">UPDATE</span><span style="FONT-FAMILY: 宋体">命令，有两条</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">语句<span style="LETTER-SPACING: -1pt">——</span></span><span style="LETTER-SPACING: -1pt"> </span><span style="FONT-FAMILY: 宋体">一条语句用于插入或更新数据，另一条语句用于重新从数据库中选择数据行。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">这些看起来多余的子句是使客户机上的数据与服务器上数据重新保持同步的一种方式。默认情况下，在插入时这些语句会应用到列上，否则数据库的触发器就会更新已插入</span><span lang="EN-US">/</span><span style="FONT-FAMILY: 宋体">更新记录中的列，数据的重新同步有一些优点。用于重新选择数据的</span><span lang="EN-US" style="FONT-SIZE: 9pt">@</span><span lang="EN-US">CustomerID</span><span style="FONT-FAMILY: 宋体">参数与主键码的</span><span lang="EN-US">INSERT/UPDATE</span><span style="FONT-FAMILY: 宋体">语句中的值相等<span style="LETTER-SPACING: -1pt">——</span></span><span lang="EN-US" style="LETTER-SPACING: -1pt"> </span><span style="FONT-FAMILY: 宋体">名称是由向导自动生成的。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">对于包含</span><span lang="EN-US">IDENTITY</span><span style="FONT-FAMILY: 宋体">列的表，生成的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">会在插入语句后使用</span><span lang="EN-US" style="FONT-SIZE: 9pt">@@</span><span lang="EN-US">IDENTITY</span><span style="FONT-FAMILY: 宋体">值，如第</span><span lang="EN-US">21</span><span style="FONT-FAMILY: 宋体">章所述，利用</span><span lang="EN-US" style="FONT-SIZE: 9pt">@@</span><span lang="EN-US">IDENTITY</span><span style="FONT-FAMILY: 宋体">生成主键码，会产生一些恼人的错误，因此要手工修改</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">的这个地方。同样，如果没有计算好列，在更新了一些数据后，重新选择源表中的所有列就会浪费时间。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 17pt"><span style="FONT-FAMILY: 宋体">向导生成的代码可以工作，但有时它并不是最佳的。对于产品系统，所有生成的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">语句都应用存储过程的调用来替换。如果</span><span lang="EN-US">INSERT</span><span style="FONT-FAMILY: 宋体">或</span><span lang="EN-US">UPDATE</span><span style="FONT-FAMILY: 宋体">子句不需要重新同步数据，删除多余的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">子句可以加速应用程序的运行。</span></p></div>
<!-- page -->
<div class="page" style="text-align: center">
<a href="100165628.htm">上一页</a> <a href="index.html">首页</a> <a href="100165630.htm">下一页</a>
</div>
<div style="margin: 0px auto; width: 700px; border: solid 1px #0b5f98;">
<div style="float: left; width: 16px; background-color: #0b5f98; color: White; padding: 1px;">
图书导读
</div>
<div style="float: right; width: 670px; text-align: left; line-height: 16pt; padding-left: 2px">
<!--导读-->
<h1 id="divCurrentNode2" style="color: #b83507; width: 100%; text-align: left; font-size: 12px; padding-left: 2px">当前章节:<a href='100165629.htm'><font color='red'>22.3.2 选择数据</font></a></h1>
<div id="divRealteNod2" style="padding-left: 2px">
<div style='float:left;width:49%'>·<a href='100165626.htm'>22.2.2 数据绑定对象</a></div><div style='float:right;width:49%'>·<a href='100165627.htm'>22.3 Visual Studio .NET和数据访问</a></div><div style='float:left;width:49%'>·<a href='100165628.htm'>22.3.1 创建一个连接</a></div><div style='float:right;width:49%'>·<a href='100165630.htm'>22.3.3 生成DataSet</a></div><div style='float:left;width:49%'>·<a href='100165631.htm'>22.3.4 更新数据源</a></div><div style='float:right;width:49%'>·<a href='100165632.htm'>22.3.5 构建模式</a></div></div>
</div>
</div>
</div>
<!-- 评论 -->
<!-- 今日推荐 -->
</div>
<!-- 页脚 -->
<div id="foot">
<img src="../../book/readbook.aspx@node=5629&bookid=16&bookname=22.3.2++_25d1_25a1_25d4_25f1_25ca_25fd_25be_25dd" alt="" width="0" height="0" />
<style>
</div>
</body>
</html>
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?