How to specify foreign key property for one to zero..one relation using fluent api in Entity Framework

Question

I have a table User and another table Company. A User can have a zero or one company registered.

User (1)---> (0..1) Company

My user class:

public class User {
    public string Id {get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }

    public string FullName
    {
        get { return FirstName + " " + LastName; }
    }

    //Relations
    public virtual Company Company { get; set; }

}

and my company class is:

public class Company {
    public int Id { get; set; }        
    public string CompanyName { get; set; }
    public string TaxNumber { get; set; }
    public string TaxOffice { get; set; }
    public string OfficeTel { get; set; }
    public string FaxNumber { get; set; }
    public string WebSite { get; set; }
    public string Address { get; set; }
    public string About { get; set; }

    //keys
    public int CityId { get; set; }
    public int StateId { get; set; }                
    public string UserId { get; set; }

    //relations
    public City City { get; set; }
    public State State { get; set; }        
    public User User { get; set; }
}

the fluent api used for company is like this:

public class CompanyConfiguration : EntityTypeConfiguration<Company>
{
    public CompanyConfiguration()
    {
        this.HasRequired(x => x.User)
            .WithOptional(x => x.Company);

        this.HasRequired(x => x.City)
            .WithMany(x => x.Companies).HasForeignKey(x => x.CityId).WillCascadeOnDelete(false);

        this.HasRequired(x => x.State)
            .WithMany(x => x.Companies).HasForeignKey(x => x.StateId).WillCascadeOnDelete(false);

        this.Property(x => x.Address).HasMaxLength(400);
        this.Property(x => x.CompanyName).HasMaxLength(100).IsRequired();
        this.Property(x => x.FaxNumber).HasMaxLength(20);
        this.Property(x => x.OfficeTel).HasMaxLength(20);
        this.Property(x => x.TaxNumber).HasMaxLength(20).IsRequired();
        this.Property(x => x.TaxOffice).HasMaxLength(50).IsRequired();
        this.Property(x => x.WebSite).HasMaxLength(200);            
    }
}

After I run Add-Migration what I expect is that UserId used as foreign key for User in Company table, but what is generated by Entity framework migrations is:

CreateTable(
            "dbo.Companies",
            c => new
                {
                    Id = c.Int(nullable: false, identity: true),
                    CompanyName = c.String(nullable: false, maxLength: 100),
                    TaxNumber = c.String(nullable: false, maxLength: 20),
                    TaxOffice = c.String(nullable: false, maxLength: 50),
                    OfficeTel = c.String(maxLength: 20),
                    FaxNumber = c.String(maxLength: 20),
                    WebSite = c.String(maxLength: 200),
                    Address = c.String(maxLength: 400),
                    About = c.String(),
                    CityId = c.Int(nullable: false),
                    StateId = c.Int(nullable: false),
                    UserId = c.String(),
                    User_Id = c.String(nullable: false, maxLength: 128),
                })
            .PrimaryKey(t => t.Id)
            .ForeignKey("dbo.Cities", t => t.CityId)
            .ForeignKey("dbo.States", t => t.StateId)
            .ForeignKey("dbo.AspNetUsers", t => t.User_Id)
            .Index(t => t.CityId)
            .Index(t => t.StateId)
            .Index(t => t.User_Id);

Question is how can I force Entity Framework to use my specified property as foreign key for relation, and the reason for this is I need the userId value of a company frequently in my code, and I don't want to use Company.User.Id expression to get that.

Note: I use Entity Framework 6.1.2 and asp.net mvc 5

Answer 1

Here is how I would define the foreignkey in this relationship:

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

   [Required]
   [Key, ForeignKey("User")]
   public string UserId { get; set; }       

   public User User { get; set; }
}

Answer 2

A bit late to the party but just throwing my thoughts in in-case anyone else comes across this question.

Had the same problem myself, Entity framework (EF6) does not seem to have a baked in way of specifying the foreign key for a 1-2-0/1 relationship, however its important to remember it is designed to be overwritten if required. The only way I could configure this was to manually amend the auto-generated migration file.

Example below is an abbreviated version of the auto-generated migration code (as posted above) showing the UserId that was intended to be the FK and the automatically added property User_Id that was inserted by EF to be the FK

    CreateTable(
        "dbo.Companies",
        c => new
            {
                Id = c.Int(nullable: false, identity: true),
                ...
                UserId = c.String(),
                User_Id = c.String(nullable: false, maxLength: 128),
            })
        .PrimaryKey(t => t.Id)
        ...
        .ForeignKey("dbo.AspNetUsers", t => t.User_Id)
        ...
        .Index(t => t.User_Id);

To achieve the original intention of the UserId being the FK, simply delete the autogenerated property then amend the FK statement and the index statement

    CreateTable(
        "dbo.Companies",
        c => new
            {
                Id = c.Int(nullable: false, identity: true),
                ...
                UserId = c.String(nullable: false, maxLength: 128),

            })
        .PrimaryKey(t => t.Id)
        ....
        .ForeignKey("dbo.AspNetUsers", t => t.UserId)
        ...
        .Index(t => t.UserId);

NB The Down method to revert the Migration is not shown in the question but any additions or amendments made to the Up method need to be reflected in the Down method as well.