{"id":5323,"date":"2007-10-17T13:20:00","date_gmt":"2007-10-17T13:20:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/vbteam\/2007\/10\/17\/linq-cookbook-recipe-9-dynamic-sort-order-doug-rothaus\/"},"modified":"2024-07-05T14:39:42","modified_gmt":"2024-07-05T21:39:42","slug":"linq-cookbook-recipe-9-dynamic-sort-order-doug-rothaus","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/vbteam\/linq-cookbook-recipe-9-dynamic-sort-order-doug-rothaus\/","title":{"rendered":"LINQ Cookbook, Recipe 9: Dynamic Sort Order (Doug Rothaus)"},"content":{"rendered":"

Ingredients:<\/p>\n

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·         <\/span><\/span><\/span>Visual Studio 2008 (Beta2 or Higher)<\/span><\/p>\n

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Categories:<\/span><\/b> LINQ-To-XML<\/p>\n

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Introduction:<\/p>\n

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You can use the Order By<\/b> clause to easily sort the results of a LINQ query in Visual Basic. A common requirement for sorted data, however, is that the user be able to choose the fields that the results are sorted by. The Order By<\/b> clause requires that you specify a static list of sort fields and sort directions, so how do you specify a sort order when you don’t know which fields the user has chosen until run time? The solution is to use the OrderBy<\/b> or OrderByDescending<\/b> query methods of the Queryable<\/b> or Enumerable<\/b> class.<\/p>\n

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Here’s how it works: The OrderBy<\/b> or OrderByDescending<\/b> methods can be applied to any LINQ query. The input to the OrderBy<\/b> or OrderByDescending<\/b> methods is either a Lambda expression, or the address of a custom function. The Lambda expression or custom function evaluate an instance of the range variable for the current query scope and return a value to be used when sorting. For example, if the range variable is a <\/font><\/span>Customer<\/span> object that has <\/font><\/span>FirstName<\/span> and <\/font><\/span>LastName<\/span> properties, you can create a function called <\/font><\/span>GetSortValue<\/span> that takes, as input, a <\/font><\/span>Customer<\/span> object and returns the value for either the <\/font><\/span>FirstName<\/span> or <\/font><\/span>LastName<\/span> property value, based on which field the user selected to sort by.<\/p>\n

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This recipe shows how to create a custom function to provide values to be used when sorting a LINQ query.<\/p>\n

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Instructions:<\/p>\n

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·         <\/span><\/span><\/span>Create a new Windows Forms Application in Visual Basic. Set the Size<\/b> of the default Form<\/b>, <\/font><\/span>Form1<\/span>, to <\/font><\/span>800, 600<\/span>.<\/p>\n

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·         <\/span><\/span><\/span>From the Toolbox<\/span><\/b>, drag a WebBrowser<\/b> control onto the form. The name of the WebBrowser<\/b> control will default to <\/font><\/span>WebBrowser1<\/span>. In the WebBrowser Tasks<\/span><\/b> panel, select Undock in parent container<\/span><\/b> and resize the WebBrowser<\/b> control to make room for two Label<\/b> controls on the form.<\/p>\n

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·         <\/span><\/span><\/span>From the Toolbox<\/span><\/b>, drag a Label<\/b> control onto the form. Set the Text<\/b> property of the Label<\/b> control to <\/font><\/span>Date<\/span>. The name of the Label<\/b> control will default to <\/font><\/span>Label1<\/span>.<\/p>\n

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·         <\/span><\/span><\/span>From the Toolbox<\/span><\/b>, drag another Label<\/b> control onto the form. Set the Text<\/b> property of the Label control to <\/font><\/span>Title<\/span>. The name of the Label<\/b> control will default to <\/font><\/span>Label2<\/span>.<\/p>\n

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·         <\/span><\/span><\/span>Right-click the Form<\/b> and select View Code<\/span><\/b>.<\/p>\n

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At this point, you will add a method that your application will use to retrieve an RSS feed to use as data to be sorted, and another method that will format the query results as a\nn HTML document to be displayed using the WebBrowser<\/b> control.<\/p>\n

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·         <\/span><\/span><\/span>In the <\/font><\/span>Form1<\/span> class, add the following code.<\/p>\n

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  <\/span>Private<\/span> rss As<\/span> XElement<\/p>\n

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  <\/span>‘ GetRssDocument: Retrieves an RSS XML document from a supplied URL.<\/p>\n

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  <\/span>Private<\/span> Function<\/span> GetRssDocument(ByVal<\/span> url As<\/span> String<\/span>) As<\/span> XElement<\/p>\n

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    <\/span>Dim<\/span> request = Net.WebRequest.Create(url)<\/p>\n

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    <\/span>Dim<\/span> response = request.GetResponse()<\/p>\n

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    <\/span>Dim<\/span> reader = Xml.XmlReader.Create(response.GetResponseStream())<\/p>\n

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    <\/span>reader.MoveToContent()<\/p>\n

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    <\/span>Dim<\/span> rssDoc = XDocument.ReadFrom(reader)<\/p>\n

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    <\/span>reader.Close()<\/p>\n

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    <\/span>response.Close()<\/p>\n

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    <\/span>Return<\/span> rssDoc<\/p>\n

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  <\/span>End<\/span> Function<\/p>\n

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‘ GetHtmlDocument: Returns HTML transformed from a list of XML elements from<\/p>\n

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  <\/span>‘                  <\/span>an RSS feed.<\/p>\n

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  <\/span>Private<\/span> Function<\/span> GetHtmlDocument(ByVal<\/span> items As<\/span> IEnumerable(Of<\/span> XElement))<\/p>\n

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    <\/span>Dim<\/span> htmlDoc = <<\/span>html<\/span>><\/p>\n

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 &nbsp\n;                  <\/span><<\/span>head<\/span>><\/p>\n

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                      <\/span><<\/span>style<\/span>><\/p>\n

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                        <\/span>td {font-family:verdana;font-size:12px}<\/p>\n

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                      <\/span><\/<\/span>style<\/span>><\/p>\n

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                    <\/span><\/<\/span>head<\/span>><\/p>\n

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                    <\/span><<\/span>body<\/span>><\/p>\n

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                      <\/span><<\/span>table<\/span> border<\/span>=<\/span>“<\/span>0<\/span>“<\/span> cellspacing<\/span>=<\/span>“<\/span>2<\/span>“<\/span>><\/p>\n

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                        <\/span><%=<\/span> _<\/p>\n

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                          <\/span>From<\/span> item In<\/span> items _<\/p>\n

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                          <\/span>Select<\/span> <<\/span>tr<\/span>><\/p>\n

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                                   <\/span><<\/span>td<\/span> style<\/span>=<\/span>“<\/span>width:480<\/span>“<\/span>><<\/span>b<\/span>><\/span><%=<\/span> item.<<\/span>title><\/span>.Value %><\/span><\/<\/span>b<\/span>><\/<\/span>td<\/span>><\/p>\n

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                                   <\/span><<\/span>td<\/span>><\/span><%=<\/span> item.<<\/span>pubDate><\/span>.Value %><\/span><\/<\/span>td<\/span>><\/p>\n

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                                 <\/span><\/<\/span><\/span><\/p><\/p>\n","protected":false},"excerpt":{"rendered":"

Ingredients: ·         Visual Studio 2008 (Beta2 or Higher)   Categories: LINQ-To-XML   Introduction: You can use the Order By clause to easily sort the results of a LINQ query in Visual Basic. A common requirement for sorted data, however, is that the user be able to choose the fields that the results are sorted by. […]<\/p>\n","protected":false},"author":260,"featured_media":8818,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[192,195],"tags":[59,93,94,117,166],"class_list":["post-5323","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-featured","category-visual-basic","tag-doug-rothaus","tag-linq-cookbook","tag-linqvb9","tag-orcas","tag-vb2008"],"acf":[],"blog_post_summary":"

Ingredients: ·         Visual Studio 2008 (Beta2 or Higher)   Categories: LINQ-To-XML   Introduction: You can use the Order By clause to easily sort the results of a LINQ query in Visual Basic. A common requirement for sorted data, however, is that the user be able to choose the fields that the results are sorted by. […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts\/5323","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/users\/260"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/comments?post=5323"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/posts\/5323\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/media\/8818"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/media?parent=5323"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/categories?post=5323"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/vbteam\/wp-json\/wp\/v2\/tags?post=5323"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}