The property cannot be configured as navigation property

Question

I am trying to implement a domain model like this:

This is an entity framework mvc application. The code for the model looks like this:

public class Login
{
    [Key]
    public int LoginID { get; set; }

    public virtual Therapist Therapist { get; set; }

    public virtual Patient Patient { get; set; }
}

public class Patient
{
    [Key]
    [ForeignKey("Login")]
    [Display(Name = "No.")]
    public int PatientId { get; set; }

    [ForeignKey("Therapist")]
    public int TherapistId { get; set; }

    [ForeignKey("Therapist")]
    public int TherapistId{ get; set; }

    public virtual Therapist Therapist { get; set; }

    public virtual Login Login { get; set; }
}

public class Therapist
{
    [Key]
    [ForeignKey("Login")]
    [Display(Name = "No.")]
    public int TherapistId { get; set; }

    [ForeignKey("Login")]
    public int LoginId { get; set; }

    public virtual Login Login { get; set; }

    public virtual ICollection<Patient> Patients { get; set; }
}

I follow exactly what is in the tutorials and stack overflow questions, and no matter what I do, when I try to run the controller, I get the same error:

Unable to retrieve metadata for 'Patient'. The property "TherapistId" cannot be configured as navigation property. The property must be a valid entity type and the property should have non-abstract getter and setter. For collection properties the type must implement ICollection where T is a valid entity type

I have no idea what is wrong with TherapistId - maybe the whole idea of the model is rubbish?

Answer 1

I think your specific error in this case is that you have

[ForeignKey("TherapistId")]
public int? TherapistId { get; set; }

instead of

[ForeignKey("Therapist")]
public int? TherapistId { get; set; }

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In any event, you do seem to have a few problems, maybe something like this (I only preserved relationship properties):

public class Login
{
    [Key]
    public int LoginID { get; set; }

    public virtual Therapist Therapist { get; set; }
    public virtual Patient Patient { get; set; }
}

public class Patient
{
    [Key]
    [ForeignKey("Login")]
    [Display(Name = "No.")]
    public int PatientId { get; set; }

    public virtual Login Login { get; set; }

    // was this supposed to be optional?
    [ForeignKey("Therapist")]
    public int? TherapistId{ get; set; }

    public virtual Therapist Therapist { get; set; }
  }

public class Therapist
{
    [Key]
    [ForeignKey("Login")]
    [Display(Name = "No.")]
    public int TherapistId { get; set; }
    public virtual Login Login { get; set; }

    public virtual ICollection<Patient> Patients { get; set; }
}

Usually, for one-to-one relationships in EF, both sides of the relationship must have the same primary key.

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In fact, for what you're doing, maybe you could try using inheritance of some sort between Login, Patient, and Therapist, because at the moment, a Login could have both a Patient and Therapist.