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POEntity Framework: LINQ to Entities only supports casting Entity Data Model primitive types
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  1. POEntity Framework: LINQ to Entities only supports casting Entity Data Model primitive types
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    copied!<p>I wrote a method to allow for an Expression to be passed in for the orderby clause, but I ran into this problem.</p> <blockquote> <p>Unable to cast the type 'System.DateTime' to type 'System.IComparable'. LINQ to Entities only supports casting Entity Data Model primitive types.</p> </blockquote> <p>Basically the expression is this:</p> <pre><code>Expression&lt;Func&lt;K, IComparable&gt;&gt; orderBy </code></pre> <p>And is used like this:</p> <pre><code>SomeEntities.SomeTable .Where ( whereClause ) .Select ( selectClause ) .OrderBy(orderBy) </code></pre> <p>The idea is so that I can use a dictionary to hold string matches to expressions like:</p> <pre><code>_possibleSortForForumItem.Add("CreateDate", item =&gt; item.CreateDate); </code></pre> <p>Then I have a method that takes in the sort string and returns the expression if it matches a key in the dictionary, if not returns some default. (The idea being a way to control what it can be ordered by) Now this works for String properties, but so far not for datetime or integer as I get the error message above. </p> <p>Now far as I (loosely) understand the problem is that Entity Framework needs it to be a Primary/EDM type because it has to convert the C# DateTime into something the database can handle.</p> <p>Is there a way to convert the datetime to a primitive type so that this will still work?</p> <p><strong>Solution</strong></p> <p>The method for getting the order by method: (Take in a query and return it in "ordered form")</p> <pre><code>private static Func&lt;IQueryable&lt;ForumViewItem&gt;, IOrderedQueryable&lt;ForumViewItem&gt;&gt; GetMethodForSort(String sortBy) { if (_methodForSort == null) { _methodForSort = new Dictionary&lt;String, Func&lt;IQueryable&lt;ForumViewItem&gt;, IOrderedQueryable&lt;ForumViewItem&gt;&gt;&gt;(); _methodForSort.Add(SortForumViewItemCreatedOn, item =&gt; item.OrderBy(innerItem =&gt; innerItem.CreatedOn)); ... } Func&lt;IQueryable&lt;ForumViewItem&gt;, IOrderedQueryable&lt;ForumViewItem&gt;&gt; orderMethod; if(String.IsNullOrEmpty(sortBy) || !_methodForSort.ContainsKey(sortBy)) { orderMethod = _methodForSort["ForumName"]; } else { orderMethod = _methodForSort[sortBy]; } return orderMethod; } </code></pre> <p>The method signature for the generic query method:</p> <pre><code>IList&lt;K&gt; GetListForGrid&lt;T, K&gt;(this ObjectQuery&lt;T&gt; query, ... Func&lt;IQueryable&lt;K&gt;, IOrderedQueryable&lt;K&gt;&gt; orderBy, ...) </code></pre> <p>And the use of the passed in method:</p> <pre><code>initialQuery = query .Where ( somethingEqualsSomething ) .Select ( selectClause ); var orderedQuery = orderBy(initialQuery); returnValue = orderedQuery .Skip(numberToShow * realPage) .Take(numberToShow) .ToList(); </code></pre>
 

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