Entity framework code-first null foreign key - entity-framework

Question

I have a User < Country model. A user belongs to a country, but may not belong to any (null foreign key).
How do I set this up? When I try to insert a user with a null country, it tells me that it cannot be null.
The model is as follows:
public class User{
public int CountryId { get; set; }
public Country Country { get; set; }
}
public class Country{
public List<User> Users {get; set;}
public int CountryId {get; set;}
}
Error: A foreign key value cannot be inserted because a corresponding primary key value does not exist. [ Foreign key constraint name = Country_Users ]"}

Answer 1

You must make your foreign key nullable:
public class User
{
public int Id { get; set; }
public int? CountryId { get; set; }
public virtual Country Country { get; set; }
}

Answer 2

I prefer this (below):
public class User
{
public int Id { get; set; }
public int? CountryId { get; set; }
[ForeignKey("CountryId")]
public virtual Country Country { get; set; }
}
Because EF was creating 2 foreign keys in the database table: CountryId, and CountryId1, but the code above fixed that.

Answer 3

I have the same problem now ,
I have foreign key and i need put it as nullable,
to solve this problem you should put
modelBuilder.Entity<Country>()
.HasMany(c => c.Users)
.WithOptional(c => c.Country)
.HasForeignKey(c => c.CountryId)
.WillCascadeOnDelete(false);
in DBContext class
I am sorry for answer you very late :)

Answer 4

I recommend to read Microsoft guide for use Relationships, Navigation Properties and Foreign Keys in EF Code First, like this picture.
Guide link below:
https://learn.microsoft.com/en-gb/ef/ef6/fundamentals/relationships?redirectedfrom=MSDN