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POOptions for code sharing in Linq2SQL expressions
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  1. POOptions for code sharing in Linq2SQL expressions
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    copied!<p>I have a pair of Linq to SQL queries which contain the same complex Where clause, specifically:</p> <pre><code>where ((range.MinimumFrequency &lt;= minFreq &amp;&amp; minFreq &lt;= range.MaximumFrequency) || (range.MinimumFrequency &lt;= maxFreq &amp;&amp; maxFreq &lt;= range.MaximumFrequency) || (range.MinimumFrequency &lt;= minFreq &amp;&amp; maxFreq &lt;= range.MaximumFrequency) || (range.MinimumFrequency &gt;= minFreq &amp;&amp; maxFreq &gt;= range.MaximumFrequency)) </code></pre> <p>And rather than copy and paste this chunk of code all over the place, I wanted to refactor it out into something else that can be shared. I know I can't do this with a normal method as it cannot be translated into SQL, but I also can't get the </p> <blockquote> <p>Expression &lt; Func&lt;...>></p> </blockquote> <p>things <a href="http://social.msdn.microsoft.com/forums/en-US/linqprojectgeneral/thread/ce3e3721-ded0-4dc6-a40a-ddeb981c2ebe/" rel="nofollow noreferrer">described here</a> to work either.</p> <p>If I simplify the where clause for the purpose of my sanity here, I want to turn</p> <pre><code>where (range.MinumumFrequency &lt; minFreq) </code></pre> <p>into an expression, so I tried:</p> <pre><code>public static Expression&lt;Func&lt;FreqRange, bool&gt;&gt; Overlaps(decimal minMHz, decimal maxMHz) { return (range =&gt; range.MinimumFrequency &lt;= minMHz); } </code></pre> <p>This appears to compile, but I can't seem to get the where statement to work, I have tried the following:</p> <pre><code>where FreqRange.Overlaps(minMHz, maxMHz) </code></pre> <p>but this gives me a compile time error:</p> <blockquote> <p>Cannot implicitly convert type 'System.Linq.Expressions.Expression>' to 'bool'</p> </blockquote> <p>Any ideas? Also, assuming we get this working, can I simply extend the lambda expression in the Expression &lt; Func &lt;>> to include the other conditions?</p>
 

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