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POCan I create a LINQ-to-Entity query on non-Entity Member fields
 

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  1. POCan I create a LINQ-to-Entity query on non-Entity Member fields
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    <p>I have an Entity class that I have extended using the <code>partial class</code> syntax to have some derived properties. I would like to perform a query using the <code>IQueryable&lt;T&gt;</code> interface that uses the information from these fields, but I currently get an exception that states</p> <blockquote> <p>The specified type member 'Title' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.</p> </blockquote> <p>Here are the relevant code snippets. You may assume that the Entity object has a String member named <code>Id</code>. </p> <pre><code>public partial class MyEntityObject { public String Title { get { return MyStrings.ResourceManager.GetString(Id) ?? ""; } } } /** * Throws exception trying to sort on the 'Title' field of a 'MyEntityObject' */ public IEnumerable&lt;T&gt; Query&lt;T&gt;(String fieldName, int low, int high) { // Get the ObjectContext&lt;T&gt; using a Repository pattern var query = context.GetRepository&lt;T&gt;() // Create an OrderBy clause based on the field by dynamically building an expression tree // see http://stackoverflow.com/questions/4546463/help-with-linq-and-generics-using-getvalue-inside-a-query PropertyInfo propertyInfo = typeof(T).GetProperty(fieldName); ParameterExpression e = Expression.Parameter(typeof(T), "e"); MemberExpression mexpr = Expression.MakeMemberAccess(e, propertyInfo); IQueryable&lt;T&gt; sortedQuery = query.OrderBy(Expression.Lambda&lt;Func&lt;T,Object&gt;&gt;(mexpr, e)); return sortedQuery.Skip(low).Take(high - low + 1).AsEnumerable(); } </code></pre> <p>As a last resort I can always do the <code>AsEnumerable()</code> before the <code>Skip</code> and <code>Take</code>, but that will involve retrieving <strong>all</strong> of the objects from the database even if the selection can be done by SQL.</p> <p>Perhaps the best alternative is to use reflection to check that the object property has a <code>DataMemberAttribute</code> and then chose to do either <code>query.OrderBy().Skip().Take().AsEnumerable()</code> or <code>query.AsEnumerable().OrderBy().Skip().Take()</code>?</p>
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