Linq 查询对象集合的问题

[t101lian]

List<PositionInfo> PositionInfoList = new List<PositionInfo>();
      PositionInfoList  = from ps in context.Position
                     join pt in context.PositionTemplate on ps.PositionTemplateId equals pt.Id
                     join jb in context.JobGrade on pt.JobGradeId equals jb.Id
                     join ptp in context.PositionType on pt.PositionTypeId equals ptp.Id
                    select new
                  {
                          JobGradeId = jb.Id,
                          JobGradeName = jb.Name,
                           PositionTypeId = ptp.Id,
                            PositionTypeName = ptp.Name,
                            PositionId = ps.Id
                        };

上面的代码提示无法隐式转换，修改后如下，但是修改后，PositionInfoList 的值就变成了null，这是什么原因，求大侠赐教。！

      PositionInfoList  = (from ps in context.Position
                     join pt in context.PositionTemplate on ps.PositionTemplateId equals pt.Id
                     join jb in context.JobGrade on pt.JobGradeId equals jb.Id
                     join ptp in context.PositionType on pt.PositionTypeId equals ptp.Id
                    select new
                  {
                          JobGradeId = jb.Id,
                          JobGradeName = jb.Name,
                           PositionTypeId = ptp.Id,
                            PositionTypeName = ptp.Name,
                            PositionId = ps.Id
                        }) as  List<PositionInfo> ;

[满庭花醉三千客]

List<PositionInfo> PositionInfoList = new List<PositionInfo>();
      PositionInfoList  = (from ps in context.Position
                     join pt in context.PositionTemplate on ps.PositionTemplateId equals pt.Id
                     join jb in context.JobGrade on pt.JobGradeId equals jb.Id
                     join ptp in context.PositionType on pt.PositionTypeId equals ptp.Id
                    select new PositionInfo
                  {
                          JobGradeId = jb.Id,
                          JobGradeName = jb.Name,
                           PositionTypeId = ptp.Id,
                            PositionTypeName = ptp.Name,
                            PositionId = ps.Id
                        }).ToList();

select new 的时候 初始化对象 PositionInfo 然后tolist集合