📄 nbear - 支持基于操作符重载的强类型where及orderby查询 - teddy's knowledge base - 博客园.htm
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<H2><A id=viewpost1_TitleUrl
href="http://www.cnblogs.com/teddyma/archive/2006/08/27/487843.html">NBear -
支持基于操作符重载的强类型Where及OrderBy查询</A> </H2>
<P>从v2.2.1版起，<A style="COLOR: #0000ff"
href="http://sf.net/projects/nbear">NBear</A>开始支持强类型的实体查询语法。例如，我们可以以如下的语法查询需要的数据：</P>
<P><SPAN
style="FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">[] users =
gateway.Select<</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">>(</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">_Entity.</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">.Id
> 5 | _Entity.</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">.LoginId
== </SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #800000; FONT-FAMILY: 'Verdana'">"teddy"</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">,
_Entity.</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">.Id.Desc
& _Entity.</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">.LoginId.Asc</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">);</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'"> </SPAN></P>
<P>注意黑体部分，Select函数的两个参数分别为两个强类型表达式，一个是一组查询条件，另一个是排序条件。 </P>
<P>以上代码等价于： </P>
<P><SPAN
style="FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">[] users =
gateway.Select<</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #008080; FONT-FAMILY: 'Verdana'">LocalUser</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">>(</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">"[Id]
> @Id or [LoginId] = @LoginId</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">"</SPAN><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">,
"[Id] desc, [LoginId]", new object[] { 5, "teddy" }</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'">);</SPAN><SPAN
style="FONT-SIZE: 9pt; COLOR: #000000; FONT-FAMILY: 'Verdana'"> </SPAN></P>
<P>我们可以看到，采用第一种语法的好处有： <BR><BR>· 强类型，对于代码错误拥有编译器错误检查； </P>
<P>· 更直观； </P>
<P>· 独立与数据库特定的SQL语法，从而隔离了业务层和特定数据库的耦合； </P>
<P><SPAN style="FONT-WEIGHT: bold">使用Entity Configurator生成强类型实体查询代码</SPAN></P>
<P>要让程序能够访问到_Entity命名空间下的这些强类型查询对象，需要先使用Entity Configurator生成强类型实体查询代码。只需在Entity
Configurator中载入实体程序集，设置要对应的元数据，点击工具的Code->Generate EntityQuery
Code菜单项，再将生成的代码复制到需要的任意程序集中，生成的代码及包含了所有实体的强类型查询对象。</P>
<P><SPAN style="FONT-WEIGHT: bold">可用操作符</SPAN></P>
<P>NBear的像类型实体查询语法支持的操作符有：&(与)，|(或)，==(等于)，!=(不等于)，>(大于)，<(小与)，>=(大于等于)，<=(小于等于)，!(否)，以及.Like()注意，Like是一个函数，可以以_Entity.User.LoginId.Like("teddy")这样的方式使用。</P>
<P>对于OrderBy部分，唯一的可用操作符是&，即表示组合多个排序条件。<BR><BR><STRONG>代码示例</STRONG><BR><BR>下面的代码是使用Entity
Configurator工具为<A style="COLOR: #0000ff"
href="http://www.cnblogs.com/teddyma/archive/2006/08/25/486312.html">使用Entity
Configurator设置实体元数据、生成数据库创建脚本</A>一文中所示的实体生成的强类型实体查询代码：<BR><BR></P>
<DIV
style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><IMG
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/None.gif"
align=top><SPAN style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">namespace</SPAN><SPAN
style="COLOR: #000000"> _Entity<BR><IMG
id=Codehighlighter1_26_3003_Open_Image
onclick="this.style.display='none'; Codehighlighter1_26_3003_Open_Text.style.display='none'; Codehighlighter1_26_3003_Closed_Image.style.display='inline'; Codehighlighter1_26_3003_Closed_Text.style.display='inline';"
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/ExpandedBlockStart.gif"
align=top><IMG id=Codehighlighter1_26_3003_Closed_Image style="DISPLAY: none"
onclick="this.style.display='none'; Codehighlighter1_26_3003_Closed_Text.style.display='none'; Codehighlighter1_26_3003_Open_Image.style.display='inline'; Codehighlighter1_26_3003_Open_Text.style.display='inline';"
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/ContractedBlock.gif"
align=top> </SPAN><SPAN
id=Codehighlighter1_26_3003_Closed_Text
style="BORDER-RIGHT: #808080 1px solid; BORDER-TOP: #808080 1px solid; DISPLAY: none; BORDER-LEFT: #808080 1px solid; BORDER-BOTTOM: #808080 1px solid; BACKGROUND-COLOR: #ffffff"><IMG
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/dot.gif"></SPAN><SPAN
id=Codehighlighter1_26_3003_Open_Text><SPAN style="COLOR: #000000">{<BR><IMG
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">public</SPAN><SPAN
style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">class</SPAN><SPAN
style="COLOR: #000000"> AgentUser<BR><IMG
id=Codehighlighter1_67_451_Open_Image
onclick="this.style.display='none'; Codehighlighter1_67_451_Open_Text.style.display='none'; Codehighlighter1_67_451_Closed_Image.style.display='inline'; Codehighlighter1_67_451_Closed_Text.style.display='inline';"
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/ExpandedSubBlockStart.gif"
align=top><IMG id=Codehighlighter1_67_451_Closed_Image style="DISPLAY: none"
onclick="this.style.display='none'; Codehighlighter1_67_451_Closed_Text.style.display='none'; Codehighlighter1_67_451_Open_Image.style.display='inline'; Codehighlighter1_67_451_Open_Text.style.display='inline';"
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/ContractedSubBlock.gif"
align=top> </SPAN><SPAN
id=Codehighlighter1_67_451_Closed_Text
style="BORDER-RIGHT: #808080 1px solid; BORDER-TOP: #808080 1px solid; DISPLAY: none; BORDER-LEFT: #808080 1px solid; BORDER-BOTTOM: #808080 1px solid; BACKGROUND-COLOR: #ffffff"><IMG
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/dot.gif"></SPAN><SPAN
id=Codehighlighter1_67_451_Open_Text><SPAN style="COLOR: #000000">{<BR><IMG
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">public</SPAN><SPAN
style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">static</SPAN><SPAN
style="COLOR: #000000"> PropertyItem LoginId </SPAN><SPAN
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">new</SPAN><SPAN
style="COLOR: #000000"> PropertyItem(</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">LoginId</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">, </SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">[</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">, </SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">]</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">, </SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">@</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">);<BR><IMG
src="NBear - 支持基于操作符重载的强类型Where及OrderBy查询 - Teddy's Knowledge Base - 博客园_files/InBlock.gif"
align=top> </SPAN><SPAN
style="COLOR: #0000ff">public</SPAN><SPAN
style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">static</SPAN><SPAN
style="COLOR: #000000"> PropertyItem Id </SPAN><SPAN
style="COLOR: #000000">=</SPAN><SPAN style="COLOR: #000000"> </SPAN><SPAN
style="COLOR: #0000ff">new</SPAN><SPAN
style="COLOR: #000000"> PropertyItem(</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">Id</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">, </SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">[</SPAN><SPAN
style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">, </SPAN><SPAN
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style="COLOR: #000000">"</SPAN><SPAN style="COLOR: #000000">, </SPAN><SPAN
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