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POHow can I create a dynamic Select on an IEnumerable<T> at runtime?
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  1. POHow can I create a dynamic Select on an IEnumerable<T> at runtime?
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    copied!<p>Given that I have an <code>IEnumerable&lt;T&gt;</code>, where <code>T</code> is any object, how can I select a specific property from it, given that I know the name of the one of the property names at run time as a string?</p> <p>For example:</p> <pre><code>var externalIEnumerable = DataPassedFromConsumingCode(); // `IEnumerable&lt;T&gt;` string knownPropertyName = "Foo"; var fooSelect = externalIEnumerable.Select(...); </code></pre> <p>In essence, I'm obviously just doing <code>externalIEnumerable.Select(x=&gt; x.Foo);</code>, but I need to perform this <code>Select</code> at runtime, when I don't have control over when it's initially created.</p> <p>-- </p> <p><strong>ANSWER:</strong> Based on AlanT's answer, here's what I actually did:</p> <pre><code>public Expression&lt;Func&lt;TItem, object&gt;&gt; SelectExpression&lt;TItem&gt;(string fieldName) { var param = Expression.Parameter(typeof(TItem), "item"); var field = Expression.Property(param, fieldName); return Expression.Lambda&lt;Func&lt;TItem, object&gt;&gt;(field, new ParameterExpression[] { param }); } </code></pre> <p>I kept it as an Expression, because calling <code>Compile</code> caused the IQueryable to be Enumerated, which meant the database was hit unnecessarily. So, to use it, I just do the following:</p> <pre><code>string primaryKey = _map.GetPrimaryKeys(typeof(TOriginator)).Single(); var primaryKeyExpression = SelectExpression&lt;TOriginator&gt;(primaryKey); var primaryKeyResults = query.Select(primaryKeyExpression).ToList(); </code></pre>
 

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