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POconstruct expression tree in run time
 

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    <p>is it possible to construct MethodCallExpression (by using Expression.Call), when this call is NESTED? so, in design time, the actual sequnce (IQueryable or IEnumerable) which the call should be run against, is unknown?</p> <p>Example:<br> let's say this is the query:<br> <code> var result = data.GroupBy(x =&gt; x.Name).Select(grouping =&gt; grouping.OrderByDescending(x =&gt; x.Date).Take(1).FirstOrDefault()).ToList(); </code> </p> <p>when data is a list of objects contains:Name,Date properties.<br> How do i constructs this query block: <code> grouping =&gt; grouping.OrderByDescending(x =&gt; x.Date) </code> using Expression.call?</p> <p>thanks</p> <p>My Answer:<br> I managed to sort this out.<br> Aducci gave me the direction, thnks! the key was to use ParameterExpression and not an actual collection instance.<br> From here, the sulotion is just around the corner: complie the Expression>, and call the compiled result with the actual collection.<br> this was very helpful: <a href="https://stackoverflow.com/questions/1367353/adding-a-method-call-to-a-linq-expression-whilst-remaining-an-full-expression">MethodCallExpression -> compiled expression </a><br> and also : <a href="https://stackoverflow.com/questions/3885516/expression-call-calling-linq-extension-firstordefault-where">link</a> </p> <p>i'm adding my final code: </p> <pre><code> Expression&lt;Func&lt;Data,DateTime&gt;&gt; lmbd = x =&gt; x.Date; ParameterExpression par = Expression.Parameter(typeof(IQueryable&lt;Data&gt;),"pname"); ParameterExpression[] parameters = new ParameterExpression[] {par}; MethodCallExpression method = Expression.Call(typeof(Queryable),"OrderBy",new Type[]{typeof(Data),typeof(DateTime)},par, lmbd); var lambaExpression = Expression.Lambda&lt;Func&lt;IQueryable&lt;Data&gt;, IQueryable&lt;Data&gt;&gt;&gt;(method, par); var compiled = lambaExpression.Compile(); </code></pre> <p>Thank you all!</p>
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    1. COcan someone explain why CreateQuery can't be use to build this expression tree? when i try to call CreateQuery with 'lambaExpression' it throws 'Argument expression is not valid'.
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