Left join once in for all

LeftJoin.cs

                var Context = new CSPRedemptionEntities();
                var List = from cp in Context.CouponPools
                           join cb in Context.CouponBatches
                                   on new { CouponBatch_id = cp.CouponBatch_id } equals
                                      new { CouponBatch_id = cb.id }
                           join m in Context.Members
                                   on new { RedeempBy_id = cp.RedeemBy.Value } equals
                                      new { RedeempBy_id = m.id} into MemberLeft
                           from x in MemberLeft.DefaultIfEmpty()
                           where cp.CouponBatch_id == CouponBatch_id && cp.Campaign_id == Campaign_id
                           orderby cp.Seq
                           select new CouponDTO {
                                        id                =cp.id                        ,
                                        Issuer_id         =cb.Campaign.Issuer_id        ,
                                        Campaign_id       =cp.Campaign_id               ,
                                        Campaign_name     =cb.Campaign.Name             ,
                                        CouponBatch_id    =cp.CouponBatch_id            ,
                                        Keyid             =cp.Keyid                     ,
                                        Lot               =cp.Lot                       ,
                                        Seq               =cp.Seq                       ,
                                        Check_digit       =cp.Check_digit               ,
                                        Generated_id      =cp.Generated_id              ,
                                        SerialNo          =cp.SerialNo                  ,
                                        IsMarketed        =cp.IsMarketed                ,
                                        RedeemFlag        =cp.RedeemFlag                ,
                                        Reward_id         =cp.Reward_id                 ,
                                        CreateDate        =cp.CreateDate                ,
                                        CreateTime        =cp.CreateTime                ,
                                        CreateBy          =cp.CreateBy                  ,
                                        RedeemDate        =cp.RedeemDate                ,
                                        RedeemTime        =cp.RedeemTime                ,
                                        RedeemBy          =cp.RedeemBy                  ,
                                        Member_name       =x.Name == null ? "" : x.Name ,
                                        PointPerCoupon    =cb.PointPerCoupon  
                                    };
                return List.ToList();