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POExpression tree and AND condition
 

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    <p>i'm trying to build a filter expression to filter data from the database.</p> <p>I've wrote the following extension to build expression dynamically depending on the selected filter parameters:</p> <pre><code>public static Expression&lt;Func&lt;T, bool&gt;&gt; And&lt;T&gt;( this Expression&lt;Func&lt;T, bool&gt;&gt; leftExpression, Expression&lt;Func&lt;T, bool&gt;&gt; rightExpression) { var invocationExpression = Expression.Invoke(rightExpression, leftExpression.Parameters.Cast&lt;Expression&gt;()); var andExpression = Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;( Expression.AndAlso(leftExpression.Body, invocationExpression), leftExpression.Parameters); return andExpression; } </code></pre> <p>I'm using it in such way:</p> <pre><code>Expression&lt;Func&lt;MyObject, bool&gt;&gt; expression = x =&gt; true; if(MyFilter.SomeParam) { expression = expression.And(x=&gt;x.MyProperty == MyFilter.SomeParam); } </code></pre> <p>It works great with NHibernate, but when i'm using this code with Entity Framework 5 it fails with the following exception message:</p> <blockquote> <p>The LINQ expression node type 'Invoke' is not supported in LINQ to Entities.</p> </blockquote> <p>There is one workaround that fetches the whole collection from the database and then applies filter conditions through the <code>IEnumerable.Where(Func&lt;T1, T2&gt; filterClause)</code>, but it dont need all data just to get one record while <code>Expression&lt;Func&lt;T1, T2&gt;&gt;</code> expressions are translated directly into SQL statement.</p> <p>Is there any simple way to make this code work with Entity Framework?</p>
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