实体化的实体框架模型错误

Question

i am using asp.net mvc5 app. I got generalize entities for following database structure that is diploma_markscheme and non_diploma_MarkScheme...

now i have model class as these table as

ElementMarkScheme

[Table("ElementMarkScheme")]
public class ElementMarkScheme : IElementMarkScheme
{
    public ElementMarkScheme()
    {

    }

    [Key]
    public int ElementMarkSchemeID { get; set; }

    public int QualificationElementID { get; set; }

    public int MarkSchemeID { get; set; }

    public DiplomaMarkScheme DiplomaMarkScheme { get; set; }
    public MarkScheme MarkScheme { get; set; }
    public Non_DiplomaMarkScheme Non_DiplomaMarkScheme { get; set; }
    public QualificationElement QualificationElement { get; set; }

}

Diploma_markscheme

[Table("DiplomaMarkScheme")]
public class DiplomaMarkScheme : IDiplomaMarkScheme 
{
    public DiplomaMarkScheme()
    {

    }

    [Key]
    public int ElementMarkSchemeID { get; set; }

    [Required(ErrorMessage = "Required Pass Mark")]
    [Display(Name = "Pass Mark")]
    public int PassMark { get; set; }


    [Display(Name = "Available Mark")]
    public int AvailableMark { get; set; }

    public ElementMarkScheme ElementMarkScheme { get; set; }

}

Non_Diploma_MarkScheme

 [Table("Non_DiplomaMarkScheme")]
public class Non_DiplomaMarkScheme : INon_DiplomaMarkScheme
{
    public Non_DiplomaMarkScheme()
    {

    }

    [Key]
    public int ElementMarkSchemeID { get; set; }

    [Required(ErrorMessage = "Required Pass Mark")]
    [Display(Name = "Pass Mark")]
    public int PassMark { get; set; }

    [Required(ErrorMessage = "Required Merit Mark")]
    [Display(Name = "Merit Mark")]
    public int MeritMark { get; set; }

    [Required(ErrorMessage = "Required Distinction Mark")]
    [Display(Name = "Distinction Mark")]
    public int DistinctionMark { get; set; }

    [Display(Name = "Available Mark")]
    public int AvailableMark { get; set; }

    public ElementMarkScheme ElementMarkScheme { get; set; }
}

at run time I get following Error I believe I am missing something or doing wrong in model class....

An exception of type 'System.InvalidOperationException' occurred in EntityFramework.dll but was not handled in user code

Additional information: Unable to determine the principal end of an association between the types 'LEO.DAL.Model.ElementMarkScheme' and 'LEO.DAL.Model.DiplomaMarkScheme'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.

Answer 1

Honestly, your database is kind of odd to me. Why is your primary key for DiplomaMarkScheme a foreign key to ElementMarkSchemeID? Anyway, it appears as though you are trying to achieve a one-to-one relationship, so please consult this document http://weblogs.asp.net/manavi/archive/2011/05/01/associations-in-ef-4-1-code-first-part-5-one-to-one-foreign-key-associations.aspx wherein the proper models are configured like so:

public class User
{
    public int UserId { get; set; }
    public string Name { get; set; }
    public int BillingAddressId { get; set; }
    public int DeliveryAddressId { get; set; }

    public Address BillingAddress { get; set; }
    public Address DeliveryAddress { get; set; }
}

public class Address
{
    public int AddressId { get; set; }
    public string Street { get; set; }
    public string City { get; set; }
    public string ZipCode { get; set; }
}

public class Context : DbContext
{
    public DbSet<User> Users { get; set; }
    public DbSet<Address> Addresses { get; set; }
}

And add this override to your DbContext class:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<User>()
                .HasRequired(a => a.BillingAddress)
                .WithMany()
                .HasForeignKey(u => u.BillingAddressId);

    modelBuilder.Entity<User>()
                .HasRequired(a => a.DeliveryAddress)
                .WithMany()
                .HasForeignKey(u => u.DeliveryAddressId);
}

If you are trying, instead, to implement a different type of relationship, let me know and I'll try to help. You may want to consider restructuring your database in a more logical way, as I can't seem to understand the way you have it setup currently.