实体框架为1个关系添加了3个外键

Question

I have a simple User Class

public class User
{
    public int ID { get; set; }
    [Required]
    public virtual ApplicationUser LoginID { get; set; }

    [Required]
    public string Name { get; set; }

    public string JobTitle { get; set; }

    [DefaultValue(UserRole.Standard)]
    public UserRole Role { get; set; }

    public virtual Company Company { get; set; }

    public string Email { get { return LoginID.Email; } }

    public bool HasAccess(UserRole TargetRole)
    {
     //Non-relevant logic
    }
}

And I also have a Company class defined as

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

        [Required]
        [MaxLength(length: 70)]
        public string Name { get; set; }

        public virtual ICollection<User> Employees { get; set; }
        public virtual ICollection<CompanyEmailDomain> Domains { get; set; }
        public ICollection<User> Managers { get { return Employees.Where(x => x.Role == UserRole.Manager).ToList(); } }
    }

However, when I run the add-migration command, it tries to add 3 Foreign keys on the User table to the Company table. Can anyone tell me why this would be the case?

AddColumn("dbo.Users", "Company_ID", c => c.Int());
AddColumn("dbo.Users", "Company_ID1", c => c.Int());
AddColumn("dbo.Users", "Company_ID2", c => c.Int());

Answer 1

Entity Framework simply counts the associations between User and Company . It detects three of them:

1. Company in User .
2. Employees in Company
3. Managers in Company

They're all 1-n ( Company - User ), so, EF concludes, User needs three foreign keys.

You know that Managers is a computed property. In fact, the property shouldn't even be be mapped. You should add the [NotMapped] attribute to it or map it as ignored by the fluent mapping API.

Also, you know that User.Company and Company.Employees are two ends of one association. But because of the two ICollection<User> properties, EF doesn't know which one to choose for the other end (the inverse end ) of User.Company .

Now if you unmap Company.Managers , EF will see two properties -- User.Company and Company.Employees -- and assume they belong together. So by unmapping one property, only one foreign key will be created.