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21.4 快速数据访问：数据读取器
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C#高级编程（第3版）
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21.4 快速数据访问：数据读取器
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165599.htm'>21.3 命令</a></div><div style='float:right;width:49%'>·<a href='100165600.htm'>21.3.1 执行命令</a></div><div style='float:left;width:49%'>·<a href='100165601.htm'>21.3.2 调用存储过程</a></div><div style='float:right;width:49%'>·<a href='100165603.htm'>21.5 管理数据和关系：DataSet类</a></div><div style='float:left;width:49%'>·<a href='100165604.htm'>21.5.1 数据表</a></div><div style='float:right;width:49%'>·<a href='100165605.htm'>21.5.2 数据列</a></div></div>
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<link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 11.4pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 11.4pt"><a ftel="_Toc507815163"><span lang="EN-GB">21.4 </span></a><span style="FONT-FAMILY: 楷体_GB2312">快速数据访问：数据读取器</span></h3>
<p class="MsoNormal"><a ftel="datareaders"><span style="FONT-FAMILY: 宋体">数据读取器</span><span lang="EN-US">(data reader)</span></a><span style="FONT-FAMILY: 宋体">是从一个数据源中选择某些数据的最简单快捷的方法，但这也是功能最弱的一个方法。不能直接实例化数据阅读器，即实例是调用</span><span lang="EN-US">ExecuteReader()</span><span style="FONT-FAMILY: 宋体">方法后从相应数据库的命令对象中返回的。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">下面的代码说明了如何从</span><span lang="EN-US">Northwind</span><span style="FONT-FAMILY: 宋体">数据库的</span><span lang="EN-US">Customer</span><span style="FONT-FAMILY: 宋体">表中选择数据。这个示例连接了数据库，选择许多记录，循环所选的记录，并把它们输出到控制台上。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这个示例使用</span><span lang="EN-US">OLE DB</span><span style="FONT-FAMILY: 宋体">提供程序作为一个来自</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">提供程序的简要的数据暂存器。在大多数情况下，</span><span lang="EN-US">OleDbClient</span><span style="FONT-FAMILY: 宋体">类与</span><span lang="EN-US">SqlClient</span><span style="FONT-FAMILY: 宋体">类是一对一的关系，例如</span><span lang="EN-US">OleDbConnection</span><span style="FONT-FAMILY: 宋体">对象就类似于在前面的示例中所使用的</span><span lang="EN-US">SqlConnection</span><span style="FONT-FAMILY: 宋体">对象。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">要对</span><span lang="EN-US">OLE DB</span><span style="FONT-FAMILY: 宋体">数据源执行命令，应使用</span><span lang="EN-US">OleDbCommand</span><span style="FONT-FAMILY: 宋体">类。下面的代码执行一个简单的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">语句，读取记录，返回一个</span><span lang="EN-US">OleDbDataReader</span><span style="FONT-FAMILY: 宋体">对象。</span></p>
<p class="MsoNormal"><a ftel="OleDbCommand1"><span style="FONT-FAMILY: 宋体">注意下面的第二个</span><span lang="EN-US">using</span></a><span style="FONT-FAMILY: 宋体">语句使</span><span lang="EN-US">OleDb</span><span style="FONT-FAMILY: 宋体">类可用。</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">using System;</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">using System.Data.OleDb;</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">目前所利用的所有数据提供程序都在同一个</span><span lang="EN-US">DLL</span><span style="FONT-FAMILY: 宋体">中</span><span style="FONT-FAMILY: 宋体">，</span><span style="FONT-FAMILY: 宋体">所以只需要引用</span><span lang="EN-US">System.Data.dll</span><span style="FONT-FAMILY: 宋体">程序集</span><span style="FONT-FAMILY: 宋体">，</span><span style="FONT-FAMILY: 宋体">就可以导入本节使用的所有类</span><span style="FONT-FAMILY: 宋体">：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-GB">public class DataReaderExample</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> public static void Main(string[] args)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> {</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> string source = "Provider=SQLOLEDB;" +</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> "server=(local)\\NetSDK;" +</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> "</span><span lang="EN-GB"> </span><span lang="EN-GB">integrated security=SSPI;" + </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> "database=northwind";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> string select = "SELECT ContactName,CompanyName FROM Customers";</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> OleDbConnection conn = new OleDbConnection(source);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> conn.Open();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> OleDbCommand cmd = new OleDbCommand(select , conn);</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> OleDbDataReader aReader = cmd.ExecuteReader();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> while(aReader.Read())</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> Console.WriteLine("'{0}' from {1}" , </span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> aReader.GetString(0) , aReader.GetString(1));</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> aReader.Close();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> conn.Close();</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 14.5pt; FTEL: 18.45pt"><span lang="EN-GB"> }</span></p>
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