C#WebAPI根据参数生成Lambda表达式

public async Task<IHttpActionResult> GetLogInfo(string userName=null,string beginTime=null,string endTime=null,string module=null,int pageIndex=1,int pageSize=20)
        {
            try
            {
                var loggerPredicate = PredicateBuilder.New<Logger>(f=>true);
                if (userName != null)
                {
                    loggerPredicate.And(l=>l.UserName==userName);
                }
                if (beginTime != null)
                {
                    var begintime = DateTime.Parse(beginTime);
                    loggerPredicate.And(l=>l.HappenedTime>=begintime);
                }
                if (endTime != null)
                {
                    var endtime = DateTime.Parse(endTime);
                    loggerPredicate.And(l => l.HappenedTime <= endtime);
                }
                if (module != null)
                {
                    loggerPredicate.And(l=>l.Module==module);
                }

                var loggerList = loggerActionSet.GetPagedList(
                        predicate: loggerPredicate,
                        selector: l => l,
                        orderBy: ll => ll.OrderByDescending(l => l.HappenedTime),
                        pageSize: pageSize,
                        pageIndex: pageIndex - 1
                        );

                return Json(new {
                    result = true,
                    data = new {
                        loggerList.HasNextPage,
                        loggerList.HasPreviousPage,
                        loggerList.PageIndex,
                        loggerList.PageSize,
                        loggerList.TotalCount,
                        loggerList.TotalPages,
                        loggerList.IndexFrom,
                        Items=loggerList.Items.Select(l=> new
                        {
                            l.Id,
                            HappenedTime = l.HappenedTime.ToString("yyyy-MM-dd hh:mm:ss"),
                            l.UserName,
                            l.Module,
                            l.Description,
                            OperationResult = l.OperationResult == true ? "成功" : "失败"
                        }),
                    }
                });

            }
            catch (Exception)
            {
                return Json(new {result=false,msg="系统错误" });
            }
        }