linq left join

linq  left join
var list = from SCR in db.SO_ChangeRec
                       join SMU in db.SP_Material on SCR.UpMaterialNo equals SMU.MaterialNo into temp
                       from tt in temp.DefaultIfEmpty()
                       join PR in db.SP_SPReservation on SCR.SOID equals PR.SOID
                       join SMD in db.SP_Material on SCR.DownMaterialNo equals SMD.MaterialNo
                       where SCR.DownPartsSN == DownPartsSN
                       && SCR.BranchID == BranchID
                       && SCR.Status == ESDStaticClass.OverStatus.NotReturned
                       && PR.PRStatus == ESDStaticClass.PRStatus.Over
                       orderby SCR.CreateTime
                       select new SparePartsChanageExt
                       {
                           ChangeRecID = SCR.ChangeRecID,
                           SOID = SCR.SOID,
                           DownPartsSN = SCR.DownPartsSN,
                           DownMaterialNo = SCR.DownMaterialNo,
                           DownMaterialNoDesc = SMD.MaterialName,
                           DownYakuan = SMD.YakuanPrice,
                           RequirementType = ESDStaticClass.RequirementCategory.Borrow,
                           DownSPMark = SCR.DownSPMark,
                           UpPartsSN = SCR.UpPartsSN,
                           UpMaterialNo = SCR.UpMaterialNo,
                           UpYakuan = tt.YakuanPrice,
                           PRCode = PR.PRCode,
                           UpMaterialNoDesc = tt.MaterialName,
                           StoreAreaType = ESDStaticClass.StoreAreaType.BadStoreArea
                       };