已知类型的Expression.Lamda？

Question

I have a Generic Sort method we use and need to extend it to be able to sort lists of different types.

When I pass in one list, the code to build the sortExpression won't work because the list items are inherited and thus the parent type is reflected in T vs. the real type which is passed in o.

Any ideas how I can make this work with the passed type?

public static List<T> Sort<T>(IQueryable<T> list, int sortOrder, string sortColumn, Type o)
{            
    var param = Expression.Parameter(o);
    MemberExpression sortProperty = Expression.Property(param, sortColumn);
    String propertyType = o.GetProperty(sortColumn).PropertyType.ToString();
    switch (propertyType)
    {
        case "System.String":
            {
                var sortExpression = Expression.Lambda<Func<T, String>>(sortProperty, param);
                return sortOrder == 0 ? list.OrderBy(sortExpression).ToList() : list.OrderByDescending(sortExpression).ToList();
            }
        case "System.Int32":
            {
                var sortExpression = Expression.Lambda<Func<T, Int32>>(sortProperty, param);
                return sortOrder == 0 ? list.OrderBy(sortExpression).ToList() : list.OrderByDescending(sortExpression).ToList();
            }
        case "System.Decimal":
            {
                var sortExpression = Expression.Lambda<Func<T, Decimal>>(sortProperty, param);
                return sortOrder == 0 ? list.OrderBy(sortExpression).ToList() : list.OrderByDescending(sortExpression).ToList();
            }
     //  etc...
    }
}

Answer 1

You can use Expression.Convert() if necessary, and you can use list.ElementType to get the type of the elements in the IQueryable.

For example:

public static List<T> Sort<T>(IQueryable<T> list, int sortOrder, string sortColumn, Type o)
{            
    var param = Expression.Parameter(list.ElementType);
    MemberExpression sortProperty = Expression.Property(Expression.Convert(param, o), sortColumn);
     //  etc...

Answer 2

尝试将PropertyType作为Expression.Lambda（）中的第一个参数发送