Linq-C#左连接

  var list = (from dr in dt_project.AsEnumerable()
                        join d1 in list_businessclass on dr.Field<Guid?>("BusinessClass") equals d1.ID into temp0
                        from tp0 in temp0.DefaultIfEmpty()
                        join d2 in list_dic_ppmodle on dr.Field<Guid?>("SanctionPPMode") equals d2.ID into temp1
                        from tp1 in temp1.DefaultIfEmpty()
                        join d3 in list_dic_ppmodle on dr.Field<Guid?>("RealPPMode") equals d3.ID into temp2
                        from tp2 in temp2.DefaultIfEmpty()
                        select new
                        {
                            ProjectID = dr.Field<Guid?>("ProjectID"),
                            ResponsibleUnit = dr.Field<Guid?>("ResponsibleUnit"),
                            OwnerUnitName = dr.Field<string>("OwnerUnitName"),//,
                            ProjectName = dr.Field<string>("ProjectName"),
                            BusinessClass = dr.Field<Guid?>("BusinessClass"),
                            BusinessClassText = (tp0 == null ? "" : tp0.Title),
                            //设立
                            EstablishedTime = dr.Field<DateTime?>("EstablishedTime") == null ? "" : Convert.ToDateTime(dr.Field<DateTime?>("EstablishedTime")).ToString("yyyy-MM-dd"),//立项时间
                            EstablishReplyCode = dr.Field<string>("EstablishReplyCode"),//立项批复文号
                            EstablishReplyCodeAttach = dr.Field<string>("EstablishReplyCodeAttach"),//立项批复文号附件
                            //可研
                            FeasibilityStudyReplyTime = dr.Field<DateTime?>("FeasibilityStudyReplyTime") == null ? "" : Convert.ToDateTime(dr.Field<DateTime?>("FeasibilityStudyReplyTime")).ToString("yyyy-MM-dd"),//可研批复时间
                            FeasibilityStudyReplyCode = dr.Field<string>("FeasibilityStudyReplyCode"),//可研批复文号
                            FeasibilityStudyReplyCodeAttach = dr.Field<string>("FeasibilityStudyReplyCodeAttach"),//可研批复文号附件
                            //概算
                            ApproximateReplyTime = dr.Field<DateTime?>("ApproximateReplyTime") == null ? "" : Convert.ToDateTime(dr.Field<DateTime?>("ApproximateReplyTime")).ToString("yyyy-MM-dd"),//概算批复时间
                            ApproximateReplyCode = dr.Field<string>("ApproximateReplyCode"),//概算批准文号
                            ApproximateReplyCodeAttach = dr.Field<string>("ApproximateReplyCodeAttach"),//概算批准文号附件
                            ApproximateExamApprovalMoney = dr.Field<decimal?>("ApproximateExamApprovalMoney") ?? 0,//概算审批金额
                            //招投标项目信息核准招标方式表
                            ApprovedInviteBidModeTime = dr.Field<DateTime?>("ApprovedInviteBidModeTime") == null ? "" : Convert.ToDateTime(dr.Field<DateTime?>("ApprovedInviteBidModeTime")).ToString("yyyy-MM-dd"),//核准招标方式时间
                            ApprovedInviteBidModeCode = dr.Field<string>("ApprovedInviteBidModeCode"),//核准招标方式文号
                            ApprovedInviteBidModeMoney = dr.Field<decimal?>("ApprovedInviteBidModeMoney") ?? 0,//招标方式核准金额
                            ApprovedInviteBidModeBasisAttach = dr.Field<string>("ApprovedInviteBidModeBasisAttach"),//上传核准招标方式依据文件
                            IsEvaluate = dr.Field<bool?>("IsEvaluate") ?? false,//项目投资是否评审
                            ApprovedInviteBidModeBasis = dr.Field<string>("ApprovedInviteBidModeBasis"),//上传核准招标方式依据
                            //招投标项目信息结算表
                            FinalAccountMoney = dr.Field<decimal?>("FinalAccountMoney") ?? 0,//决算金额
                            ApproximateExecMoney = dr.Field<decimal?>("ApproximateExecMoney") ?? 0,//执行金额
                            IsExceedApproximate = dr.Field<bool?>("IsExceedApproximate") ?? false,//是否超出概算
                            ExceedApproximateMoney = dr.Field<decimal?>("ExceedApproximateMoney") ?? 0,//超出概算金额
                            //
                            PackageID = dr.Field<Guid?>("PackageID"),//包类型
                            PackageClassID = dr.Field<Guid?>("PackageClassID"),//包类型
                            EngineeringName = dr.Field<string>("EngineeringName"),
                            AgencyName = dr.Field<string>("AgencyName"),
                            InviteSchemeSancDept = dr.Field<string>("InviteSchemeSancDept"),
                            SanctionPPMode = dr.Field<Guid?>("SanctionPPMode"),
                            SanctionPPModeText = (tp1 == null ? "" : tp1.Title),
                            RealPPMode = dr.Field<Guid?>("RealPPMode"),
                            RealPPModeText = (tp2 == null ? "" : tp2.Title),
                            PPChangeSancDept = dr.Field<string>("PPChangeSancDept"),
                            PPChangeReason = dr.Field<string>("PPChangeReason"),
                            PPChangeBasis = dr.Field<string>("PPChangeBasis"),
                            PPChangeBasisAttach = dr.Field<string>("PPChangeBasisAttach"),
                            Media = b_common.TranslateMedia(list_media, dr.Field<string>("Media")),
                            //3
                            SignedContractTime = dr.Field<DateTime?>("SignedContractTime") == null ? "" : Convert.ToDateTime(dr.Field<DateTime?>("SignedContractTime")).ToString("yyyy-MM-dd"),
                            SignedContractMoney = dr.Field<decimal?>("SignedContractMoney") ?? 0,
                            ExecuteUnit = dr.Field<string>("ExecuteUnit"),
                            //3
                            SettlementMoney = dr.Field<decimal?>("SettlementMoney") ?? 0,
                            IsExceedApproximateForPackage = dr.Field<bool?>("IsExceedApproximateForPackage") ?? false,
                            ExceedApproximateBasis = dr.Field<string>("ExceedApproximateBasis"),
                            ExceedApproximateBasisAttach = dr.Field<string>("ExceedApproximateBasisAttach"),
                            Note = dr.Field<string>("Note")
                        }
              ).ToList();