how add entityobject with exsist object that have relational in Entity framework

Question

Hi my scenario
i want to create application for dental clinic . I have vs2010 ultimate and first time started with empty model and then I crate it with Generate database from model…… now I have afew class which some of this makes paritial by me because to extend flexible I have class with name patient and doctor that derived from Person abstract class Each person have 0..1 relation with patientcase .Each doctor have many patient and each patient have exactly 1 doctor (or relation with doctor) . in other side each patientcase hold insurance info and each insuranceinfo have relation with insurancecompany class now in my pritial class with name patient I;m try to create new patient with this constructor : Attention: new doctor and new insurance company exsist before and saved in database) And selectdoctor is variable with type doctor that hold select doctor from combobox;

  public Patient(Doctor doctorname, string n, string f, string codemeli, string datebirth, bool gender, bool material, string age, bool group,PatientCase pc,Address a,contactdetail condetail)
  {
      Doctorname.patient.add(this); // is this code right?
      selectdoctor = doctorname;
      this.Firstname = n;
      this.lastname = n;
      this.internationalcode = codemeli;
      this.dateofbirth = datebirth;
      this.gender = gender;
      this.materialstatus = material;
      if(age!="")
      this.age = int.Parse(age);
      this.group = group;
      this.PatientCase = pc;
      this.adres = a;
      this.contac = condetail;

  }

And its my save method for save patient in this class: public void save() { db = new DentalContainer(DbAccess.Get_EntityConstring());

       dr.Patient.Add(this);
       db.tblPerson.AddObject(this);
       db.SaveChanges();
   }

And it;s code from addpatient form to make new patient: Patient newpatient=new Patient (SelectDoctor,txtname.Text,txtfamily.Text,txtinternationalcode.Text,txtbirthdate.Text,get_GenderStatus(chkMan.Checked,chkWoman.Checked),get_MaterialStatus(chkunmarried.Checked,chkmarried.Checked),txtage.Text,get_group(chkMan.Checked,chkadult.Checked),npc,newaddress ,newcontacdetail);

Npc is patientcase which I create it earlyier in code above; and the pass it to patient constructor now when db.savechanges is occur this exception or error is shown: The EntityKey property can only be set when the current value of the property is null. Where is my mistake help me please?

Answer 1

(i) your constructor shouldn't add the patient to a doctor, it should just construct a Patient disconnected from any object graph (side effects in constructors are a bad idea).

(ii) you only need to connect objects to an object graph once: construct a patient and then add it to a doctor's .Patient collection, then save changes. Don't add it to the person table too.

(iii) your pluralization and table naming could be clearer - it should be dr.Patients and db.People.