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PODynamic LINQ OrderBy + Method Count
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  1. PODynamic LINQ OrderBy + Method Count
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    copied!<p>I'm displaying a table of objects <strong>Company</strong> in a webpage and I am using a Dynamic Linq OrderBy to sort them on each property. I'm using this code <a href="https://stackoverflow.com/a/233505/265122">https://stackoverflow.com/a/233505/265122</a></p> <pre><code>public static IOrderedQueryable&lt;T&gt; OrderBy&lt;T&gt;(this IQueryable&lt;T&gt; source, string property) { return ApplyOrder&lt;T&gt;(source, property, "OrderBy"); } public static IOrderedQueryable&lt;T&gt; OrderByDescending&lt;T&gt;(this IQueryable&lt;T&gt; source, string property) { return ApplyOrder&lt;T&gt;(source, property, "OrderByDescending"); } public static IOrderedQueryable&lt;T&gt; ThenBy&lt;T&gt;(this IOrderedQueryable&lt;T&gt; source, string property) { return ApplyOrder&lt;T&gt;(source, property, "ThenBy"); } public static IOrderedQueryable&lt;T&gt; ThenByDescending&lt;T&gt;(this IOrderedQueryable&lt;T&gt; source, string property) { return ApplyOrder&lt;T&gt;(source, property, "ThenByDescending"); } static IOrderedQueryable&lt;T&gt; ApplyOrder&lt;T&gt;(IQueryable&lt;T&gt; source, string property, string methodName) { string[] props = property.Split('.'); Type type = typeof(T); ParameterExpression arg = Expression.Parameter(type, "x"); Expression expr = arg; foreach(string prop in props) { // use reflection (not ComponentModel) to mirror LINQ PropertyInfo pi = type.GetProperty(prop); expr = Expression.Property(expr, pi); type = pi.PropertyType; } Type delegateType = typeof(Func&lt;,&gt;).MakeGenericType(typeof(T), type); LambdaExpression lambda = Expression.Lambda(delegateType, expr, arg); object result = typeof(Queryable).GetMethods().Single( method =&gt; method.Name == methodName &amp;&amp; method.IsGenericMethodDefinition &amp;&amp; method.GetGenericArguments().Length == 2 &amp;&amp; method.GetParameters().Length == 2) .MakeGenericMethod(typeof(T), type) .Invoke(null, new object[] {source, lambda}); return (IOrderedQueryable&lt;T&gt;)result; } </code></pre> <p>It's great but I would also like to sort the companies on the number of employees.</p> <p>Like this : <strong>query.OrderBy("Employees.Count")</strong></p> <p>I tried to call to the Count method dynamically without any success so far.</p> <p>I modified the code like this :</p> <pre><code>foreach(string prop in props) { if (prop == "Count") { var countMethod = (typeof(Enumerable)).GetMethods().First(m =&gt; m.Name == "Count").MakeGenericMethod(type); expr = Expression.Call(countMethod, expr); break; } // Use reflection (not ComponentModel) to mirror LINQ. PropertyInfo pi = type.GetProperty(prop); expr = Expression.Property(expr, pi); type = pi.PropertyType; } </code></pre> <p>But I have an exception on the <code>expr = Expression.Call(countMethod, expr);</code></p> <p>The exception is:</p> <pre><code>ArgumentException Expression of type 'System.Collections.Generic.ICollection`1[Employee]' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable`1[System.Collections.Generic.ICollection`1 [Employee]]' of method 'Int32 Count[ICollection`1] System.Collections.Generic.IEnumerable`1[System.Collections.Generic.ICollection`1 Employee]])' </code></pre> <p>Any idea on how to achieve that?</p>
 

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