ParameterExpression left = Expression.Parameter(itemType, "s");
var des = typeof(TypeExtension).GetMethod("GetDescription"); //静态扩展方法： public static string GetDescription(this Enum value) 获取枚举的描述信息
Expression pro = Expression.Property(left, itemType.GetProperty("FileType")); //属性
//var pro1 = Expression.MakeMemberAccess(left, itemType.GetProperty("FileType"));
var descall = Expression.Call(des, pro); //调用静态方法
Expression right = Expression.Call(descall, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), Expression.Constant("文")); //模糊查询