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POCalling the .Any Extension Method with Entity Framework using Expression Trees
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  1. POCalling the .Any Extension Method with Entity Framework using Expression Trees
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    copied!<p>I have looked at few examples here <a href="https://stackoverflow.com/questions/439172/calling-a-method-from-an-expression">Calling a Method from an Expression</a> and on <a href="http://msdn.microsoft.com/en-us/library/bb882637.aspx" rel="nofollow noreferrer">MSDN</a> but I have not been able to get the right method call/object type for Any() for the query below. I seem to be able to get the property call but not IEnumerable part of the child property.<br> billing_map_set_lu is the parent of billmaps_lu and is defined as an association in the Entity Framework. </p> <p>The reason I am using expression trees is that I need to be able to define the query at runtime with 1-n .SelectMany(p => p.billmaps_lu).Where(predicate) clauses. So I figured if I could build the expression trees I could handle all the different combinations I have for this system which are many. </p> <pre><code>var myResults = ctx.billing_map_set_lu .Where(p =&gt; p.billmaps_lu.Any(b =&gt; b.billmap_columnname == "templatesittings_key" &amp;&amp; b.billmap_columnvalue == 428264)) SelectMany(p =&gt; p.billmaps_lu) .Where (b =&gt;b.billmap_columnname =="locations_key" &amp;&amp; b.billmap_columnvalue == 12445) Select(z =&gt; z.billing_map_set_lu); </code></pre> <p>I have tried a quite a few attempts using the samples above... </p> <pre><code>ParameterExpression bms = Expression.Parameter(typeof(billmaps_lu)); Expression left1 = Expression.Property(bms, typeof(billmaps_lu).GetProperty("billmap_columnname")); Expression right1 = Expression.Constant("templatesittings_key", typeof(string)); Expression InsideAny1 = Expression.Equal(left1, right1); Expression left2 = Expression.Property(bms, typeof(billmaps_lu).GetProperty("billmap_columnvalue")); Expression right2 = Expression.Constant(428264, typeof(int)); Expression InsideAny2 = Expression.Equal(left2, right2); Expression myWhereClause1 = Expression.AndAlso(InsideAny1, InsideAny2); </code></pre> <p>The above part seems fine but when I try to do the .Any It is like I can't get the right property/method to get the right objects out. (I feel like I am on a physics problem where I am working with the wrong units.) I am hoping it is something simple that I am missing, I am pretty new to Expression Trees.. I have included non-working code to try to show you where my head is at and how someone can steer me in the right direction. </p> <pre><code>MethodInfo method = typeof(Enumerable).GetMethods().Where(m =&gt; m.Name == "Any" &amp;&amp; m.GetParameters().Length == 2).Single().MakeGenericMethod(typeof(billing_map_set_lu).GetProperty("billmaps_lu").PropertyType); ParameterExpression billMapSetParameter = Expression.Parameter(typeof(billing_map_set_lu), "p"); ParameterExpression billMaps = Expression.Parameter(typeof(billmaps_lu), "p1"); var myFunction = Expression.Lambda&lt;Func&lt;billmaps_lu, bool&gt;&gt;(Expression.Call(method, Expression.Property(billMapSetParameter, typeof(billing_map_set_lu).GetProperty("billmaps_lu")), myWhereClause1), billMaps) </code></pre>
 

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