使用字符串和嵌套反射

Question

根据这个question，我创建了我的数据集排序方法。

public static IOrderedQueryable<T> Order<T>(this IQueryable<T> source, string propertyName,
    ListSortDirection direction = ListSortDirection.Ascending)
{
    return ListSortDirection.Ascending == direction
        ? source.OrderBy(ToLambda<T>(propertyName))
        : source.OrderByDescending(ToLambda<T>(propertyName));
}

private static Expression<Func<T, object>> ToLambda<T>(string propertyName)
{
    var propertyNames = propertyName.Split('.');
    var parameter = Expression.Parameter(typeof(T));
    var body = propertyNames.Aggregate<string, Expression>(parameter, Expression.Property);

    return Expression.Lambda<Func<T, object>>(Expression.Convert(body, typeof(object)), parameter);
//            return Expression.Lambda<Func<T, object>>(body, parameter);
}

在我尝试将其与Nullable<DateTime>一起使用之前一切正常，我已调用Expression.Convert来封装Nullable<DateTime>，但遗憾的是它会抛出

Unable to cast the type 'System.Nullable`1[[System.DateTime, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types.

我想让这更通用，但不能带来好主意。

我已经这样做了，但它的哑巴AF：D

public static IOrderedQueryable<T> Order<T>(this IQueryable<T> source, string propertyName,
    ListSortDirection direction = ListSortDirection.Ascending)
{
    if (propertyName.Contains("date", StringComparison.CurrentCultureIgnoreCase))
    {
        return ListSortDirection.Ascending == direction
            ? source.OrderBy(ToLambda<T, DateTime?>(propertyName))
            : source.OrderByDescending(ToLambda<T, DateTime?>(propertyName));

    }
    return ListSortDirection.Ascending == direction
        ? source.OrderBy(ToLambda<T, object>(propertyName))
        : source.OrderByDescending(ToLambda<T, object>(propertyName));
}

private static Expression<Func<T, A>> ToLambda<T, A>(string propertyName)
{
    var propertyNames = propertyName.Split('.');
    var parameter = Expression.Parameter(typeof(T));
    var body = propertyNames.Aggregate<string, Expression>(parameter, Expression.Property);

    return Expression.Lambda<Func<T, A>>(Expression.Convert(body, typeof(A)), parameter);
//            return Expression.Lambda<Func<T, object>>(body, parameter);
}