如何创建动态 LINQ 连接扩展方法

有一个动态库LINQ http://en.wikipedia.org/wiki/Language_Integrated_Query扩展方法作为示例发布Visual Studio 2008 http://en.wikipedia.org/wiki/Microsoft_Visual_Studio#Visual_Studio_2008。我想用 join 方法扩展它。下面的代码在运行时因参数丢失匹配异常而失败。哪里有问题？

public static IQueryable Join(this IQueryable outer, IEnumerable inner,
                              string outerSelector, string innerSelector, string resultsSelector,
                              params object[] values)
{
    if (inner == null)
        throw new ArgumentNullException("inner");
    if (outerSelector == null)
        throw new ArgumentNullException("outerSelector");
    if (innerSelector == null)
        throw new ArgumentNullException("innerSelector");
    if (resultsSelector == null)
        throw new ArgumentNullException("resultsSelctor");

    LambdaExpression outerSelectorLambda =
        DynamicExpression.ParseLambda(outer.ElementType, null,
                                      outerSelector, values);
    LambdaExpression innerSelectorLambda =
        DynamicExpression.ParseLambda(inner.AsQueryable().ElementType,
                                      null, innerSelector, values);

    ParameterExpression[] parameters = new ParameterExpression[] {
        Expression.Parameter(outer.ElementType, "outer"),
        Expression.Parameter(inner.AsQueryable().ElementType,
        "inner")
    };
    LambdaExpression resultsSelectorLambda =
        DynamicExpression.ParseLambda(parameters, null,
                                      resultsSelector, values);

    return outer.Provider.CreateQuery(
        Expression.Call(
            typeof(Queryable), "Join", new Type[] {
                outer.ElementType,
                inner.AsQueryable().ElementType,
                outerSelectorLambda.Body.Type,
                innerSelectorLambda.Body.Type,
                resultsSelectorLambda.Body.Type
            },
            outer.Expression, inner.AsQueryable().Expression,
            Expression.Quote(outerSelectorLambda),
            Expression.Quote(innerSelectorLambda),
            Expression.Quote(resultsSelectorLambda))
        );
}

我现在已经自己修好了。这是一个小学生错误，向 CreateQuery(...) 调用传递了太多参数。将以下代码粘贴到动态 Join 扩展方法的 DynamicQueryable 类中的 Dynamic.cs 文件中。您可以在以下位置找到 DynamicQuery 示例项目的源代码：http://code.msdn.microsoft.com/csharpsamples http://code.msdn.microsoft.com/csharpsamples.
Enjoy.

    public static IQueryable Join(this IQueryable outer, IEnumerable inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values)
    {
        if (inner == null) throw new ArgumentNullException("inner");
        if (outerSelector == null) throw new ArgumentNullException("outerSelector");
        if (innerSelector == null) throw new ArgumentNullException("innerSelector");
        if (resultsSelector == null) throw new ArgumentNullException("resultsSelctor");

        LambdaExpression outerSelectorLambda = DynamicExpression.ParseLambda(outer.ElementType, null, outerSelector, values);
        LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType, null, innerSelector, values);

        ParameterExpression[] parameters = new ParameterExpression[] {
            Expression.Parameter(outer.ElementType, "outer"), Expression.Parameter(inner.AsQueryable().ElementType, "inner") };
        LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values);

        return outer.Provider.CreateQuery(
            Expression.Call(
                typeof(Queryable), "Join",
                new Type[] {outer.ElementType, inner.AsQueryable().ElementType, outerSelectorLambda.Body.Type, resultsSelectorLambda.Body.Type  },
                outer.Expression, inner.AsQueryable().Expression, Expression.Quote(outerSelectorLambda), Expression.Quote(innerSelectorLambda), Expression.Quote(resultsSelectorLambda)));
    }


    //The generic overload.
    public static IQueryable<T> Join<T>(this IQueryable<T> outer, IEnumerable<T> inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values)
    {
        return (IQueryable<T>)Join((IQueryable)outer, (IEnumerable)inner, outerSelector, innerSelector, resultsSelector, values);
    }