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POWhat is recommended pattern to bind a WPF control to a LINQ to Entity query?
 

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  1. POWhat is recommended pattern to bind a WPF control to a LINQ to Entity query?
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    <p>At the <a href="http://msdn.microsoft.com/en-us/library/bb738469.aspx" rel="nofollow">MSDN</a> you can read the following:</p> <blockquote> <p>We recommend that you not bind controls directly to an ObjectQuery. Instead, bind controls to the result of the Execute method. Binding in this manner prevents a query from being executed multiple times during binding.</p> </blockquote> <p>and</p> <blockquote> <p>If you prefer to work with LINQ queries, we recommend that you cast the result of the query to ObjectQuery and call the Execute method.</p> </blockquote> <p>My question is: Is right to cast the result of a LINQ to Entity (that is at most an IQueryable) to an ObjectQuery, a more specific type??</p> <p>Is that the right pattern to use when ones need bind a control to the result of a LINQ query?</p> <p>When I drag a data source from the Visual Studio 2010 Data Sources windows to my WPF form, two methods are generated as explained at MSDN, but in my application I need apply a filter to the "predefinedTokensQuery" variable, and that is why I wrote a LINQ query (replacing the generated initialization of the "predefinedTokensQuery" variable) and then the compiler complain because it can't cast a LINQ query to an ObjectQuery explicitly.</p> <p>The following code is how is right now in my application, it works, but I'm really worry to miss something here and not being following the recommended pattern.</p> <pre><code>private System.Data.Objects.ObjectQuery&lt;Token&gt; GetPredefinedTokensQuery(UnduplicateModelContainer unduplicateModelContainer) { // Auto generated code System.Data.Objects.ObjectQuery&lt;Unduplicate.Token&gt; predefinedTokensQuery = (System.Data.Objects.ObjectQuery&lt;Unduplicate.Token&gt;) from token in unduplicateModelContainer.Tokens where token.Predefined == true select token; // To explicitly load data, you may need to add Include methods like below: // predefinedTokensQuery = predefinedTokensQuery.Include("Tokens.Type"). // For more information, please see http://go.microsoft.com/fwlink/?LinkId=157380 // Returns an ObjectQuery. return predefinedTokensQuery; } private void windowPredefinedTokens_Loaded(object sender, RoutedEventArgs e) { Unduplicate.UnduplicateModelContainer unduplicateModelContainer = new Unduplicate.UnduplicateModelContainer(); // Load data into Tokens. You can modify this code as needed. System.Windows.Data.CollectionViewSource predefinedTokensViewSource = ((System.Windows.Data.CollectionViewSource)(this.FindResource("predefinedTokensViewSource"))); System.Data.Objects.ObjectQuery&lt;Unduplicate.Token&gt; predefinedTokensQuery = this.GetPredefinedTokensQuery(unduplicateModelContainer); predefinedTokensViewSource.Source = predefinedTokensQuery.Execute(System.Data.Objects.MergeOption.AppendOnly); } </code></pre> <p>Thanks in advanced. Frank Abel</p>
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    1. USgsi-frank
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      1. POWhat is recommended pattern to bind a WPF control to a LINQ to Entity query?
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    1. COAt http://social.msdn.microsoft.com/Forums/en/adodotnetentityframework/thread/60dbea1b-df66-4853-8411-6f144471f2d0 Daniel Simmons said "any time you use IQueryable<T> against the entity framework, you will be going through ObjectQuery<T>.", so I suppose that another related question is.... should the c# compiler recognize/transform the LINQ to Entities queries to an ObjectQuery<T> instead of IQueryable<T> to avoid such explicit cast? I'm a little confuse, can anybody explain in deep the relation between both types and how that affect the code I put above?
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    2. COThe "recommended" pattern would be MVVM nowadays. But Yes, take control over when the query is executed. Don't pay too much attention to auto-gen code, darg-and-drop is not used a lot.
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      1. POWhat is recommended pattern to bind a WPF control to a LINQ to Entity query?
      1. USHenk Holterman
    3. COThanks for the reply comment Henk, but what about the cast? Is right what MSDN document suggest? I mean, is right cast the result of a LINQ to Entity to a ObjectQuery? I'm reading right now Developer's Guide to Microsoft Prism, thanks again.
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