问如何使用刚创建的用户记录的id设置查找字段？

EN

    var clinic = new new_clinic();
            clinic.new_name = "Medinet";

            Account trust = new Account();
            trust.Name = "bIRMINGHAM CITY hOSPITAL";
            Guid trustID = (Guid)Service().Create(trust);

            CrmEntityReference clinic_trust = new CrmEntityReference(trust.LogicalName, trustID);
            clinic.new_Trust = clinic_trust;
            clinic.new_ClinicDate = DateTime.Now;

            new_hospital hospital = new new_hospital();
            hospital.new_name = "Geek-guru";
            Service().Create(hospital);
            Guid hospitalID = (Guid)hospital.Id;
            clinic.new_HostingHospital = new CrmEntityReference(hospital.LogicalName, hospitalID);

            clinic.new_ClinicDate = new DateTime(2018, 07, 28);

            new_serviceprovision ser_contract = new new_serviceprovision();
            ser_contract.new_Trust = clinic_trust;
            ser_contract.new_Specialty = new OptionSetValue(100000018);
            Service().Create(ser_contract);
            Guid ser_con_id = (Guid)ser_contract.Id;
            clinic.new_ServiceContract = new CrmEntityReference(ser_contract.LogicalName, ser_con_id);

            // Account account =  (Account)GetOrgService().Retrieve(trust.LogicalName, trustID, new Microsoft.Xrm.Sdk.Query.ColumnSet("name"));

            //retreive the default business unit needed to create the user
            QueryExpression businessUnitQuery = new QueryExpression
            {
                EntityName = BusinessUnit.EntityLogicalName,
                ColumnSet = new ColumnSet("businessunitid"),
                Criteria = { Conditions = { new ConditionExpression("parentbusinessunitid", ConditionOperator.Null) } }
            };

            BusinessUnit businessUnit = Service().RetrieveMultiple(businessUnitQuery).Entities[0].ToEntity<BusinessUnit>();



            //creating a user
            SystemUser systemUser = new SystemUser();
            systemUser.DomainName = "" + "Chika";
            systemUser.FirstName = "Olabajo";
            systemUser.LastName = "Boss";
            systemUser.InternalEMailAddress = "onyebuchi@gmail.com";
            systemUser.BusinessUnitId = new EntityReference(BusinessUnit.EntityLogicalName, businessUnit.Id);
            Guid systemID = (Guid)Service().Create(systemUser);

           // systemUser = (SystemUser)Service().Retrieve(systemUser.LogicalName, systemID, new Microsoft.Xrm.Sdk.Query.ColumnSet("fullname"));

            //this field is a lookup field to User. Assigned to the user created above
            clinic.new_ClinicCoordinator = new CrmEntityReference(systemUser.LogicalName, systemID);

            clinic.new_BookedBy = new OptionSetValue(100000001);
            clinic.new_Type1 = new OptionSetValue(100000008);
            clinic.new_Type2 = new OptionSetValue(100000001);
            clinic.new_NumberofConsultants = 5;
            clinic.new_NumberofNursesSuppliedByTrust = 6;


            Service().Create(clinic);//getting error here
            MessageBox.Show("Sucessfully added a clinic record");