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POHow can I create a dynamic multi-property Select on an IEnumerable<T> at runtime?
 

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  1. POHow can I create a dynamic multi-property Select on an IEnumerable<T> at runtime?
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    <p>I asked a <a href="https://stackoverflow.com/questions/8990231/how-can-i-create-a-dynamic-select-on-an-ienumerablet-at-runtime">very similar question</a> yesterday, but it wasn't until today I realised the answer I accepted doesn't solve all my problems. I have the following code:</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>Which is used as follows:</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> <p>This allows me to pull out the primary keys from an <code>IQueryable&lt;TUnknown&gt;</code>. The problem is that this code only works with a single primary key and I need to add support for multiple PKs. </p> <p>So, is there any way I can adapt the <code>SelectExpression</code> method above to take an <code>IEnumerable&lt;string&gt;</code> (which is my list of primary key property names) and have the method return an expression that selects those keys?</p> <p>I.e. Given the following: </p> <pre><code>var knownRuntimePrimaryKeys = new string[] { "CustomerId", "OrderId" }` </code></pre> <p>My Select needs to do the following (at runtime):</p> <pre><code>var primaryKeys = query.Select(x=&gt; new { x.CustomerId, x.OrderId }); </code></pre>
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    1. COThe problem is that anonymous types that are the results of the select statemet are created at compile time..
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      1. USm0sa
    2. COIs there an alternative to using an Anonymous type and still achieve what I require? Or is it back to the drawing board?
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    3. CO@GenericTypeTea, would a Tuple be an acceptable option for you?
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      1. USThomas Levesque
 

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