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POEntity Framework 4: How to turn a string into an object for .OrderBy(p => p.fieldname)?
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copied!<p>Now this is a trick question because you <strong>cannot</strong> do this:</p> <pre><code>var a = myDB.Where(p => p.field == "filter").OrderBy("it." + fieldname); </code></pre> <p>You could change the Where to accept a string, which allows you to change the OrderBy to accept a string, but that's not the question.</p> <p><strong>How can you turn a string like "productID, productName" in to an OrderBy expression</strong>? If I am correct in thinking, maybe the question could be "how to turn a Specification Pattern in to an Expression delegate?"</p> <p>The problem is I don't know what table they want, and thus I don't know the primary key. I used generics to represent the type of table.</p> <pre><code>public interface IRepository<E, C> where C : ObjectContext // E is an Entity { void Add(E entity); void Del(E entity); IList<E> Get(Expression<Func<E, bool>> filterLambda = null, //Where clause Expression<Func<E, object>> orderbyLambda = null, //OrderBy int? page = null, //Page to get int? pageSize = null, //Page Size Expression<Func<E, object>> selectLambda = null); //Populate Fields int Count(Expression<Func<E, bool>> filterLambda = null); bool SaveChanges(); } </code></pre> <p>The actual statement I use to pull content from the data context (data container?) is </p> <pre><code>this.GetEntity().Where(filterLambda) .OrderBy(orderbyLambda) .Skip(((int)page - 1) * (int)pageSize) .Take((int)pageSize) .Select(selectLambda).ToList(); </code></pre> <p>I <strong>need</strong> the <code>OrderBy()</code> to implement <code>.Skip()</code> and <code>.Take()</code>. For all those of you who think you can do this are correct for Linq to SQL. However, Linq to Entities does not support it:</p> <pre><code>The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'. </code></pre>

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