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2009-09-23T20:33:32.723
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First, you'll access the current grouped value as <code>Key</code> in your Select clause: <pre><code>.Select("new (Key as Group, Sum(Value) as TotalValue)"); </code></pre> That should make your query work. The harder question is how to turn the returned objects, which will have a dynamically generated type that inherits from <code>DynamicClass</code>, into a static type. Option 1: Use reflection to access the dynamic object's <code>Group</code> and <code>TotalValue</code> properties. Option 2: Use compiled expression trees for lightweight code generation to access the <code>Group</code> and <code>TotalValue</code> properties. Option 3: Modify the Dynamic library to support a strongly-typed result. This turns out to be rather simple: <ol> <li>In <code>ExpressionParser.Parse()</code>, capture the type argument in a private field: <pre><code>private Type newResultType; public Expression Parse(Type resultType) { newResultType = resultType; int exprPos = token.pos; // ... </code></pre></li> <li>Near the end of <code>ExpressionParser.ParseNew()</code>, we'll try to use <code>newResultType</code> before defaulting to a dynamic type: <pre><code>Expression ParseNew() { // ... NextToken(); Type type = newResultType ?? DynamicExpression.CreateClass(properties); MemberBinding[] bindings = new MemberBinding[properties.Count]; for (int i = 0; i < bindings.Length; i++) bindings[i] = Expression.Bind(type.GetProperty(properties[i].Name), expressions[i]); return Expression.MemberInit(Expression.New(type), bindings); } </code></pre></li> <li>Finally, we need a strongly typed version of <code>Select()</code>: <pre><code>public static IQueryable<TResult> Select<TResult>(this IQueryable source, string selector, params object[] values) { if (source == null) throw new ArgumentNullException("source"); if (selector == null) throw new ArgumentNullException("selector"); LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, typeof(TResult), selector, values); return source.Provider.CreateQuery<TResult>( Expression.Call( typeof(Queryable), "Select", new Type[] { source.ElementType, typeof(TResult) }, source.Expression, Expression.Quote(lambda))); } </code></pre> The only changes from the original <code>Select()</code> are places we reference <code>TResult</code>.</li> </ol> Now we just need a named type to return: <pre><code> public class Result { public string Group { get; set; } public double TotalValue { get; set; } } </code></pre> And your updated query will look like this: <pre><code> IQueryable<Result> res = table1.AsQueryable() .GroupBy(groupbyvalue, "it") .Select<Result>("new (Key as Group, Sum(Value) as TotalValue)"); </code></pre>
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