c# 扩展LINQ的order by函数支持通过字符串来指定列名并支持多列

public static IOrderedQueryable OrderBy(this IQueryable q, string condition)
        {
            string[] conditions = condition.Split(‘,‘);

            if (conditions.Length==0)
            {
                return (IOrderedQueryable) q;
            }

            IOrderedQueryable res = null;

            for (int i = 0; i )
            {
                string[] strings = conditions[i].Split(" ");
                var fieldName = strings[0];
                var direction = strings[1];

                var param = Expression.Parameter(typeof(T), "p");
                var prop = Expression.Property(param, fieldName);
                var exp = Expression.Lambda(prop, param);

                string method;

                if (i==0)
                {
                    method = direction.ToLower() == "asc" ? "OrderBy" : "OrderByDescending";
                }
                else
                {
                    method = direction.ToLower() == "asc" ? "ThenBy" : "ThenByDescending";
                }
                Type[] types = { q.ElementType, exp.Body.Type };
                var mce = i==0? Expression.Call(typeof(Queryable), method, types, q.Expression, exp): Expression.Call(typeof(Queryable), method, types, res.Expression, exp);

                if (conditions.Length == 1)
                {
                    return (IOrderedQueryable)q.Provider.CreateQuery(mce);
                }

                res = i == 0 ? (IOrderedQueryable) q.Provider.CreateQuery(mce) : (IOrderedQueryable)res.Provider.CreateQuery(mce);
            }
            return res;

        }