Two One-to-Many relationships in the same table

Question

I have a table called SystemAccount , which (up until recently) had a MasterAccountID on it that would point to its parent account (obviously an int? ). My client has now told me that there may be sometimes where an account can have 2 parent accounts (none ever have more than that). I've been trying to make the adjustment in my SystemAccount class, but it's not generating the relationship that I want.

Here's part of the class code:

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

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

public virtual SystemAccount MasterAccount { get; set; }

public virtual SystemAccount SecondMasterAccount { get; set; }

public virtual List<SystemAccount> AllSubAccounts { get; set; }

public virtual List<SystemAccount> SecondarySubAccounts { get; set; }

When I do this I get 4 FKs in the table, 2 of which are auto-generated ( SystemAccount_ID and SystemAccount_ID1 ). I've even tried to put the [InverseProperty] attribute on MasterAccount and SecondMasterAccount to point to the Lists, and it gives me an error each time (EDIT: It gives me a NullReferenceException ).

I know that I should make it into a many-to-many relationship, but I'm facing a deadline soon, and refactoring the uses of MasterAccount and MasterAccountID would take me way beyond the deadline.

How can I get this to work?

EDIT: Exception stack trace:

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=EntityFramework
  StackTrace:
       at System.Data.Entity.ModelConfiguration.Configuration.Types.EntityTypeConfiguration.Configure(EdmEntityType entityType, EdmModel model)
       at System.Data.Entity.ModelConfiguration.Configuration.ModelConfiguration.ConfigureEntities(EdmModel model)
       at System.Data.Entity.ModelConfiguration.Configuration.ModelConfiguration.Configure(EdmModel model)
       at System.Data.Entity.DbModelBuilder.Build(DbProviderManifest providerManifest, DbProviderInfo providerInfo)
       at System.Data.Entity.DbModelBuilder.Build(DbConnection providerConnection)
       at System.Data.Entity.Infrastructure.EdmxWriter.WriteEdmx(DbContext context, XmlWriter writer)
       at System.Data.Entity.Migrations.Extensions.DbContextExtensions.<>c__DisplayClass1.<GetModel>b__0(XmlWriter w)
       at System.Data.Entity.Migrations.Extensions.DbContextExtensions.GetModel(Action`1 writeXml)
       at System.Data.Entity.Migrations.Extensions.DbContextExtensions.GetModel(DbContext context)
       at System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration, DbContext usersContext)
       at System.Data.Entity.Migrations.DbMigrator..ctor(DbMigrationsConfiguration configuration)
       at System.Data.Entity.MigrateDatabaseToLatestVersion`2.InitializeDatabase(TContext context)
       at System.Data.Entity.Database.<>c__DisplayClass2`1.<SetInitializerInternal>b__0(DbContext c)
       at System.Data.Entity.Internal.InternalContext.<>c__DisplayClass8.<PerformDatabaseInitialization>b__6()
       at System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action)
       at System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization()
       at System.Data.Entity.Database.Initialize(Boolean force)
       at Tests.Core.UI.SessionStartTests.ShouldSuccessfullyInitializeDatabase() in c:\Projects\Current\tests\Tests.Core\UI\StartTests.cs:line 72
  InnerException: 

EDIT 2: When I used Moho's suggestion:

System.Data.Entity.ModelConfiguration.ModelValidationException : One or more validation errors were detected during model generation:

\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'SystemAccount_AllSubAccounts_Target' in relationship 'SystemAccount_AllSubAccounts'. Valid values for multiplicity for the Principal Role are '0..1' or '1'.
\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'SystemAccount_AllSubAccounts_Source' in relationship 'SystemAccount_AllSubAccounts'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.
\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'SystemAccount_SecondarySubAccounts_Target' in relationship 'SystemAccount_SecondarySubAccounts'. Valid values for multiplicity for the Principal Role are '0..1' or '1'.
\tSystem.Data.Entity.Edm.EdmAssociationEnd: : Multiplicity is not valid in Role 'SystemAccount_SecondarySubAccounts_Source' in relationship 'SystemAccount_SecondarySubAccounts'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

EDIT 3: My code for updating the database:

Database.SetInitializer(new MigrateDatabaseToLatestVersion<MyDbContext, Configuration>());
var db = new MyDbContext();
db.Database.Initialize(true);

My OnModelCreating method:

modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();

modelBuilder.Entity<ClientStatisticsView>().ToTable("ClientStatistics");

base.OnModelCreating(modelBuilder);

My Configuration file:

public Configuration()
{
  AutomaticMigrationsEnabled = true;
  AutomaticMigrationDataLossAllowed = true;
}

protected override void Seed(MyDbContext context)
{
}

Answer 1

Have you tried decorating the collection properties with the InverseProperty attribute?

[InverseProperty( "MasterAccount" )]
public virtual List<SystemAccount> AllSubAccounts { get; set; }

[InverseProperty( "SecondMasterAccount" )]
public virtual List<SystemAccount> SecondarySubAccounts { get; set; }

Here's a demo that works for me:

public class HierarchicalEntity
{
    public int Id { get; set; }
    public string Description { get; set; }

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

    [ForeignKey( "SecondaryParent" )]
    public int? SecondaryParentId { get; set; }
    public virtual HierarchicalEntity PrimaryParent { get; set; }

    public virtual HierarchicalEntity SecondaryParent { get; set;}

    [InverseProperty( "PrimaryParent" )]
    public ICollection<HierarchicalEntity> ChildrenViaPrimaryParent { get; set; }

    [InverseProperty( "SecondaryParent" )]
    public ICollection<HierarchicalEntity> ChildrenViaSecondaryParent { get; set; }
}

Answer 2

I have reproduced the problem now with EF 5. I get exactly the same exception and stack trace and also the exception in your EDIT 2 when applying Moho's code. The problem does not occur with EF 6. So, if upgrading to EF 6 is an option for you that would solve the problem.

If you need to stick with EF 5 using Fluent API mapping instead of using the [InverseProperty] attribute worked for me without exceptions. You can remove all attributes then:

public class SystemAccount
{
    public int ID { get; set; }

    public int? MasterAccountID { get; set; }
    public int? SecondMasterAccountID { get; set; }

    public virtual SystemAccount MasterAccount { get; set; }
    public virtual SystemAccount SecondMasterAccount { get; set; }

    public virtual List<SystemAccount> AllSubAccounts { get; set; }
    public virtual List<SystemAccount> SecondarySubAccounts { get; set; }
}

Relationship mapping with Fluent API:

modelBuilder.Entity<SystemAccount>()
    .HasOptional(s => s.MasterAccount)
    .WithMany(s => s.AllSubAccounts)
    .HasForeignKey(s => s.MasterAccountID);

modelBuilder.Entity<SystemAccount>()
    .HasOptional(s => s.SecondMasterAccount)
    .WithMany(s => s.SecondarySubAccounts)
    .HasForeignKey(s => s.SecondMasterAccountID);

The fact that the [InverseProperty] attribute with your model causes exceptions appears to be a bug in EF 5. The bug is most likely related to the self-referencing kind of the relationships because normally with relationships between different entities the attribute works without problems.

Answer 3

My solution is based on the advice I got from @Slauma and @Moho (+1 to both of you for your help!).

It is true that the [InverseProperty] attribute is what was missing, but it wouldn't work when I just put it on the file. Then, when I tried @Moho's code in a completely new file, it still didn't work. So I switched the [ForeignKey] attributes from being on the ID fields to being on the object fields themselves, ie:

public int? PrimaryParentId { get; set; }
public int? SecondaryParentId { get; set; }

[ForeignKey( "PrimaryParent" )]
public virtual HierarchicalEntity PrimaryParent { get; set; }

[ForeignKey( "SecondaryParent" )]
public virtual HierarchicalEntity SecondaryParent { get; set;}

That ended up working. But when I tried doing that on my SystemAccount class it wouldn't work. So I ended up doing the following steps to get it to work:

1. Commented out the list objects, as well as the parent records, and the FK attribute from both fields.
2. Migrated the database. All FKs now dropped.
3. Uncommented it out
4. Checked that the [InverseProperty] attribute was on the list objects, and put the [ForeignKey] attribute on the virtual objects.
5. Migrated the database. The only FKs that show up are the ones that I want to be FKs!

I know that it's a weird solution, but as long as it works...