EF 4.1 in MVC3 using Lazy Loading - asp.net-mvc-3

Question

EF 4.1 in MVC3 and Lazy loading, using code first model
I am using Membership API for creating an account. Once the account is created successfully. I redirect to create a Contact record automatically.
contactId (auto database generated), userid (storing the user id that was generated by membership api)
The models are:
public class Contact
{
public int ContactID { set; get; }
public string UserId { set; get; }
public string LastName { set; get; }
public int? CompanyID { set; get; } // not sure if I need this as it will be NULL
public virtual Company CompanyInfo { set; get; }
}
next the user can click on create Company link or logout & login later to create the company record.
public class Company
{
public int CompanyID { set; get; }
public int ContactID { set; get; }
public string CompanyName { set; get; }
public virtual Contact Contacts { set; get; }
}
When the user decides to create company record, I am checking if company already exists, if exists I am just showing the contact information and the company information OR if not found I redirect to create company.
public ActionResult chckifCompanyFound()
{
int contactId = 1; //Assuming I retrieved the value
//I think I should get the data from Company table, if company data found then contact data could be retrieved using lazy loading?
Company c= db.Company.Include(c => c.Contacts).Where(x => x.ContactID == contactId).FirstOrDefault();
if(c == null)
//redirect to create company
else
// view data from c company object
}
currently it shows an exception once it tries to create contact record after membership API creates an account. I create the record like this:
Contact contact = new Contact();
contact.UserId = userId;
contact.LastName = lastName;
db.Contacts.Add(contact);
db.SaveChanges();
Exception:
Unable to determine the principal end of an association between the types 'D.Models.Contact' and 'D.Models.Company'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
thank you so much!

Answer 1

Try the following (from this link):
Contact cc = db.Contacts.Include( "CompanyInfo" ).Where(x => x.ContactID == product.ContactID).FirstOrDefault();

Answer 2

Try replacing your models with these:
public class Contact
{
public int ContactId { set; get; }
public string UserId { set; get; }
public int CompanyId { get; set; }
public string LastName { set; get; }
public virtual Company Company { set; get; }
}
public class Company
{
public int CompanyId { set; get; }
public string CompanyName { set; get; }
public virtual ICollection<Contact> Contacts { set; get; }
}
Your Contact needs a CompanyId since it has only a single company related to it, and it will act as a foreign key between that contact and the company. The navigation property CompanyInfo will be used for the lazy loading. Your Company object only needs the Contacts collection because the Contact is where the relationship is created in the database.
To answer your question about the query I need more information... where does the product come in to play? I don't see it referenced from the contact or company, but if you want to get the Company of a Contact, simply do this:
var company = dbContext.Contacts.Find(userId).Company;
Console.WriteLine("Company Name: {0}", company.CompanyName);

Answer 3

try:
Contact cc = db.Contacts.Include(c=>c.CompanyInfo).Where(x => x.ContactID == product.ContactID).FirstOrDefault();