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21.5.3 数据关系
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C#高级编程（第3版）
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21.5.3 数据关系
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2006-10-13 14:41:00
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<div style='float:left;width:49%'>·<a href='100165603.htm'>21.5 管理数据和关系：DataSet类</a></div><div style='float:right;width:49%'>·<a href='100165604.htm'>21.5.1 数据表</a></div><div style='float:left;width:49%'>·<a href='100165605.htm'>21.5.2 数据列</a></div><div style='float:right;width:49%'>·<a href='100165607.htm'>21.5.4 数据约束</a></div><div style='float:left;width:49%'>·<a href='100165608.htm'>21.6 XML模式</a></div><div style='float:right;width:49%'>·<a href='100165609.htm'>21.7 填充数据集</a></div></div>
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<link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><a ftel="_Toc507815166"><span lang="EN-GB">21.5.3 </span></a><span style="FONT-FAMILY: 黑体">数据关系</span></h3>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">在编写应用程序时，常常需要获取和缓存各种表的信息。</span><span lang="EN-US">DataSet</span><span style="FONT-FAMILY: 宋体">类是这些信息的容器，使用一般的</span><span lang="EN-US">OLEDB</span><span style="FONT-FAMILY: 宋体">，需要提供一种奇怪的</span><span lang="EN-US">SQL</span><span style="FONT-FAMILY: 宋体">语法来执行分层的数据关系，提供程序本身不能没有它自己的“怪癖”。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">另一方面，</span><span lang="EN-US">DataSet</span><span style="FONT-FAMILY: 宋体">类从一开始就是为建立数据表之间的关系而设计的。本节中的代码说明了如何手工生成并填充两个数据表。如果手中没有</span><span lang="EN-US">SQL Server</span><span style="FONT-FAMILY: 宋体">或</span><span lang="EN-US">NorthWind</span><span style="FONT-FAMILY: 宋体">数据库，就可以运行这个示例。</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="DataSet2"><span lang="EN-US">DataSet ds = new DataSet("Relationships");</span></a></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US">ds.Tables.Add(CreateBuildingTable());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US">ds.Tables.Add(CreateRoomTable());</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US">ds.Relations.Add("Rooms",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> ds.Tables["Building"].Columns["BuildingID"],</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> ds.Tables["Room"].Columns["BuildingID"]);</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这两个表仅包含一个主键码和名称字段，</span><span lang="EN-US">Room</span><span style="FONT-FAMILY: 宋体">表有一个</span><span lang="EN-US">BuildingID</span><span style="FONT-FAMILY: 宋体">外键码，如图</span><span lang="EN-US">21-7 </span><span style="FONT-FAMILY: 宋体">所示。</span></p>
<p align="center"><span lang="EN-US"><img height="53" src="21/image007.jpg" width="269" alt="" /></span></p>
<p style="FTEL: 8.15pt" align="center"><span style="FONT-FAMILY: 宋体">图</span><span lang="EN-US"> 21-7</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这些表都非常简单，下面的代码<span style="LETTER-SPACING: 0.2pt">迭代</span></span><span lang="EN-US" style="LETTER-SPACING: 0.2pt">Buildings</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.2pt">表中的行，并遍历数据关系，列出</span><span lang="EN-US" style="LETTER-SPACING: 0.2pt">Rooms</span><span style="FONT-FAMILY: 宋体; LETTER-SPACING: 0.2pt">表中所有的子行。</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">foreach(DataRow theBuilding in ds.Tables["Building"].Rows)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US">{</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> DataRow[] children = theBuilding.GetChildRows("Rooms");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> int roomCount = children.Length;</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("Building {0} contains {1} room{2}",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> theBuilding["Name"],</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> roomCount,</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> roomCount > 1 ? "s" : "");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> // Loop through the rooms</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; LINE-HEIGHT: 13pt; FTEL: 18.45pt"><span lang="EN-US"> foreach(DataRow theRoom in children)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("Room: {0}", theRoom["Name"]);</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 16pt"><span lang="EN-US">DataSet</span><span style="FONT-FAMILY: 宋体">类和其他分层的旧</span><span lang="EN-US">recordset</span><span style="FONT-FAMILY: 宋体">对象之间的主要区别是关系显示的方式。在分层的</span><span lang="EN-US">recordset</span><span style="FONT-FAMILY: 宋体">对象中，关系显示为行中的一个伪列，这个列本身是一个可以迭代的</span><span lang="EN-US">recordset</span><span style="FONT-FAMILY: 宋体">。但在</span><span lang="EN-US">ADO.NET</span><span style="FONT-FAMILY: 宋体">中，通过调用</span><span lang="EN-US">GetChildRows()</span><span style="FONT-FAMILY: 宋体">方法就可以遍历关系。</span></p>
<p class="a6" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">DataRow[] children = theBuilding.GetChildRows("Rooms");</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 16pt"><span style="FONT-FAMILY: 宋体">该方法有许多形式，但上面的示例只使用关系的名称在父子行之间来回遍历。它返回一组数据行，使用前面示例中的索引器就可以更新这些行。</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 16pt"><span style="FONT-FAMILY: 宋体">更有趣的数据关系是可以用两种方式遍历这些数据。在</span><span lang="EN-US">DataTable</span><span style="FONT-FAMILY: 宋体">类上使用</span><span lang="EN-US">ParentRelations</span><span style="FONT-FAMILY: 宋体">属性，可以从父数据行中找到子数据行，也可以在子记录中找到父数据行。这个属性返回一个</span><span lang="EN-US">DataRelationCollection</span><span style="FONT-FAMILY: 宋体">，该集合可以使用</span><span lang="EN-US">[]</span><span style="FONT-FAMILY: 宋体">数组语法来索引</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">例如，</span><span lang="EN-US">DataRelations[“Rooms”])</span><span style="FONT-FAMILY: 宋体">，另外，</span><span lang="EN-US">GetChildRows()</span><span style="FONT-FAMILY: 宋体">方法也可以如下所示进行调用；</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">foreach(DataRow theRoom in ds.Tables["Room"].Rows)</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"> DataRow[] parents = theRoom.GetParentRows("Rooms");</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> foreach(DataRow theBuilding in parents)</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> Console.WriteLine("Room {0} is contained in building {1}",</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> theRoom["Name"],</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span lang="EN-US"> theBuilding["Name"]);</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">}</span></p>
<p class="MsoNormal" style="LINE-HEIGHT: 16pt"><span style="FONT-FAMILY: 宋体">方法</span><span lang="EN-US">GetParentRows(</span><span style="FONT-FAMILY: 宋体">返回</span><span lang="EN-US">0</span><span style="FONT-FAMILY: 宋体">行或多行数据</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">或</span><span lang="EN-US">GetParentRow(</span><span style="FONT-FAMILY: 宋体">根据给定的某种关系检索一个父行</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">都有许多重写方法，可以检索出父行。</span></p></div>
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