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POHow do I do a left outer join with Dynamic Linq?
 

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  1. POHow do I do a left outer join with Dynamic Linq?
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    <p>I am trying to mimick the left outer join <a href="https://stackoverflow.com/questions/584820/how-do-you-perform-a-left-outer-join-using-linq-extension-methods">here</a> but using dynamic linq extension methods. What i have:</p> <pre><code>public static IQueryable SelectMany(this IQueryable source, string selector, string resultsSelector, params object[] values) { if (source == null) throw new ArgumentNullException("source"); if (selector == null) throw new ArgumentNullException("selector"); // Parse the lambda LambdaExpression lambda = DynamicExpression.ParseLambda( source.ElementType, null, selector, values); // Fix lambda by recreating to be of correct Func&lt;&gt; type in case // the expression parsed to something other than IEnumerable&lt;T&gt;. // For instance, a expression evaluating to List&lt;T&gt; would result // in a lambda of type Func&lt;T, List&lt;T&gt;&gt; when we need one of type // an Func&lt;T, IEnumerable&lt;T&gt; in order to call SelectMany(). Type inputType = source.Expression.Type.GetGenericArguments()[0]; Type resultType = lambda.Body.Type.GetGenericArguments()[0]; Type enumerableType = typeof(IEnumerable&lt;&gt;).MakeGenericType(resultType); Type delegateType = typeof(Func&lt;,&gt;).MakeGenericType(inputType, enumerableType); lambda = Expression.Lambda(delegateType, lambda.Body, lambda.Parameters); ParameterExpression[] parameters = new ParameterExpression[] { Expression.Parameter(source.ElementType, "outer"), Expression.Parameter(resultType, "inner") }; LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda( parameters, null, resultsSelector, values); // Create the new query return source.Provider.CreateQuery(Expression.Call(typeof(Queryable), "SelectMany", new Type[] { source.ElementType, resultType, resultsSelectorLambda.Body.Type }, source.Expression, Expression.Quote(lambda), Expression.Quote(resultsSelectorLambda))); } </code></pre> <p>and:</p> <pre><code>public static IQueryable GroupJoin(this IQueryable outer, IEnumerable inner, string outerKeySelector, string innerKeySelector, string resultSelector, params object[] values) { Type innerElementType = inner.AsQueryable().ElementType; var outerParameter = Expression.Parameter(outer.ElementType, "outer"); var innerParameter = Expression.Parameter(innerElementType, "inner"); var groupParameter = Expression.Parameter(typeof(IEnumerable&lt;&gt;) .MakeGenericType(innerElementType), "group"); var outerLambda = DynamicExpression.ParseLambda(new[] { outerParameter }, null, outerKeySelector, values); var innerLambda = DynamicExpression.ParseLambda(new[] { innerParameter }, outerLambda.Body.Type, innerKeySelector, values); var resultLambda = DynamicExpression.ParseLambda(new[] { outerParameter, groupParameter }, null, resultSelector, values); return outer.Provider.CreateQuery(Expression.Call(typeof(Queryable), "GroupJoin", new[] { outer.ElementType, innerElementType, outerLambda.Body.Type, resultLambda.Body.Type }, outer.Expression, Expression.Constant(inner), Expression.Quote(outerLambda), Expression.Quote(innerLambda), Expression.Quote(resultLambda))); } </code></pre> <p>However where I fall down is with the <code>DefaultIfEmpty</code> within the <code>SelectMany</code></p>
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    1. COWhich implementation of DynamicExpression are you referring to here?
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