EF6 CodeFirst ForeignKey属性映射无法按预期工作

Question

I have a many-to-1 situation where an Employee can serve many Customers and each Customer is served by 1 Employee. In the Customer class I map SupportRep to EmployeeId using the ForeignKey attribute and it gives me an error.

public class Customer
{
    [Key]
    public int CustomerId { get; set; }
    ...

    public int? SupportRepId { get; set; }

    [ForeignKey("EmployeeId")]
    public virtual Employee SupportRep { get; set; }
}

public class Employee
{
    [Key]
    public int EmployeeId { get; set; }
    ...

    [ForeignKey("SupportRepId")]
    public virtual ICollection<Customer> Customers { get; set; }
}

The error I get is:

Error: The ForeignKeyAttribute on property 'SupportRep' on type 'SqlLiteChinook. Customer' is not valid. The foreign key name 'EmployeeId' was not found on the d ependent type 'SqlLiteChinook.Customer'. The Name value should be a comma separa ted list of foreign key property names.

However, if I change EmployeeId to SupportRepId in the Customer class it works.

Shouldn't the foreign key in the Customer class point to EmployeeId of Employee class?

Please enlighten me. Thank you.

Answer 1

You're mixing things up a bit. The [ForeignKey("EmployeeId")] in your Customer class has to say which property of that class is the foreign key to Employee . The attribute doesn't go looking for the foreign key in the Employee class.

Your second mistake is declaring a foreign key on the ICollection<Customer> . Since you have a one-to-many relationship, your collection can't point to one customer, it has a relation to multiple ones. So your customer needs to have the foreign key to employee (each customer 'points' to one employee) but employee can't contain a foreign key to customer.

public class Customer
{
  [Key]
  public int CustomerId { get; set; }
  ...
  public int? SupportRepId { get; set; }

  [ForeignKey("SupportRepId")]
  public virtual Employee SupportRep { get; set; }
}

public class Employee
{
  [Key]
  public int EmployeeId { get; set; }
  ...
  public virtual ICollection<Customer> Customers { get; set; }
}

Answer 2

Try this

public class Customer
{
    [Key]
    public int CustomerId { get; set; }
    ...

    public int? SupportRepId { get; set; }

    [ForeignKey("SupportRepId")]
    public virtual Employee SupportRep { get; set; }
}

public class Employee
{
    [Key]
    public int EmployeeId { get; set; }
    ...

    public virtual ICollection<Customer> Customers { get; set; }
}