如何创建一个动态LINQ连接扩展方法

有一个动态 LINQ扩展方法的库作为样例与 VisualStudio2008发布.我想用一个连接方法来扩展它.以下代码在运行时失败,参数缺失匹配异常.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,innerSelector,values);

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

解决方法

我现在已经修好了将createquery(…)调用的参数传给过多的一个小学生错误.将以下代码粘贴到DynamicQueryable类中的Dynamic.cs文件中,以进行动态连接扩展方法.您可以在 http://code.msdn.microsoft.com/csharpsamples找到DynamicQuery示例项目的源代码.
请享用.

public static IQueryable Join(this IQueryable outer,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,values);
        LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType,values);

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

        return outer.Provider.createquery(
            Expression.Call(
                typeof(Queryable),new Type[] {outer.ElementType,resultsSelectorLambda.Body.Type  },Expression.Quote(resultsSelectorLambda)));
    }


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

原文地址：https://www.jb51.cc/csharp/96109.html