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.
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);
}
