Question

I’m new to EF, and I’ve just started a new project. I currently have a model BrandManagers with one primary key and three foreign keys. I don’t understand how I should map these in the DbContext.

public class BrandManager
{
    public int BrandManagerId { get; set; }

    [Required()]
    public int PersonId { get; set; }

    [Required()]
    public int BrandId { get; set; }

    [Required()]
    public int CountryId { get; set; }

    public virtual Person Person { get; set; }
    public virtual Brand Brand { get; set; }
    public virtual Country Country { get; set; }
}

How will I map this? I have tried the below, to no avail.

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Person>()
        .HasRequired(x => x.Country);

    modelBuilder.Entity<Brand>()
        .HasMany(x => x.BrandManagers);

    modelBuilder.Entity<BrandManager>()
        .HasRequired(x => x.Person);
    modelBuilder.Entity<BrandManager>()
        .HasRequired(x => x.Brand);
    modelBuilder.Entity<BrandManager>()
        .HasRequired(x => x.Country);

    base.OnModelCreating(modelBuilder);
    modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
}

I keep getting

Introducing FOREIGN KEY constraint ‘FK_Person_Country_CountryId’ on table ‘Person’ may cause cycles or multiple cascade paths.

I didn’t find any solutions to this specific matter in the introduction tutorials on the ASP.NET website, nor any questions regarding this matter here on SO, so I’m starting to feel like I’m misunderstanding some essential parts of EF.

Answer 1

My answer is more specific to how you map foreign keys in EF Code First. I was about to work on the second part about the multiple cascade paths, when Leniency answered and is correct. So, rather than throwing away my answer, which might be helpful to you, here is the answer to the general how to map foreign keys in EF :). With a bit on the cascading deletes at the bottom.

You can just use data annotations with no need for mapping in the ModelBuilder. However, if you don’t want your POCO object marked up with database annotations, I have also provided the solution using the modelBuilder.

Another note, you do not NEED to have PersonId as long as you have the Person reference. In that case, the generator would create the FK for you (and your POCO class would not have Id’s which it does not need). However, it is probably better practice to have the Id for lazy loading (I am not sure if that is why you did this or not).

Last, you dont even need to set up the Foreign Key if you follow conventions. So, if you have the Country class with a PK of Id, then when you create the Country reference with a CountryId also, EF will look realize through the naming that CountryId is the FK for the country reference. (Source)

Data Annotations:

public class BrandManager
{
    public int BrandManagerId { get; set; }

    [Required()]
    public int PersonId { get; set; }

    [Required()]
    public int BrandId { get; set; }

    [Required()]
    public int CountryId { get; set; }

    [ForeignKey("PersonId")]
    public virtual Person Person { get; set; }
    [ForeignKey("BrandId")]
    public virtual Brand Brand { get; set; }
    [ForeignKey("CountryId")]
    public virtual Country Country { get; set; }
}

DbContext: (Also, in this case, you should not need ANY data annotations on your POCO class because they are all being set up in the modelBuilder)

modelBuilder.Entity<BrandManager>()
    .HasRequired(x => x.Person)
    .WithMany(x=>x.People)
    .HasForeignKey(x=>x.PersonId);

As to the specific error you are getting, you will need to add .WillCascadeOnDelete(false) as Leniency pointed out to BrandManager->Country. You could remove this for the Person->Country, but it would be better to remove BrandManager because it will ultimately cascade through the Person path anyway.