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POHow to reuse a linq expression for 'Where' when using multiple source tables
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  1. POHow to reuse a linq expression for 'Where' when using multiple source tables
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    copied!<p>Let's have the following:</p> <pre><code>public interface IOne { UInt64 Id { get; } Int16 Size { get; } } public interface ITwo { UInt64 OneId { get; } Int16 Color { get; } } </code></pre> <p>As explained <a href="https://stackoverflow.com/questions/986877/how-can-i-reuse-expressions-within-linq-statements">here</a> the way to reuse a linq expression is to write something like this:</p> <pre><code>public static Expression&lt;Func&lt;IOne, bool&gt;&gt; MyWhereExpression( int value ){ return (o) =&gt; (o.Size &gt; value); } int v = 5; IQueryable&lt;IOne&gt; records = from one in s.Query&lt;IOne&gt;() .Where(MyWhereExpression(v)) select one; </code></pre> <p>When I want to do the same with two tables I encounter a problem.</p> <p>The expression:</p> <pre><code>public static Expression&lt;Func&lt;IOne, ITwo, bool&gt;&gt; MyWhereExpression2(int color ) { return (one,two) =&gt; (one.Id == two.OneId) &amp;&amp; (two.Color &gt; color ); } </code></pre> <p>Linq 1:</p> <pre><code>int color = 100; IQueryable&lt;IOne&gt; records = from one in s.Query&lt;IOne&gt;() from two in s.Query&lt;ITwo&gt;() .Where(MyWhereExpression2(color)) select one; </code></pre> <p>This doesn't work as <em>.Where</em> sticks to only the 2nd <em>from</em>.</p> <p>Linq 2:</p> <pre><code>int color = 100; IQueryable&lt;IOne&gt; records = (from one in s.Query&lt;IOne&gt;() from two in s.Query&lt;ITwo&gt;() select new { one, two }) .Where(MyWhereExpression2(color)); </code></pre> <p>This results in </p> <blockquote> <p>Argument 2: cannot convert from 'Expression&lt;System.Func&lt;IOne,ITwo,bool>>' to 'System.Func&lt;AnonymousType#1,int,bool>'</p> </blockquote> <p>I understand the error message about the AnonymousType, but I cannot figure out how to write the query.</p> <p>The reason why I want to use an expression rather than just write</p> <pre><code>where (one.Id == two.OneId) &amp;&amp; (two.Color &gt; color ) </code></pre> <p>directly in the linq query is because I want to reuse this expression in multiple linq queries. </p>
 

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