Saving navigational data as well when saving the entity - entity-framework

Question

Given the following models (I'm using EF Core):
public class Person {
public Person(){
PhoneNumbers = new HashSet<PhoneNumber>();
}
public int Id {get; set;}
public String Name {get; set;}
public virtual ICollection<PhoneNumber> PhoneNumbers { get; set; }
}
public class PhoneNumber {
public int Id {get; set;}
public String Number {get; set;}
public int PersonId {get; set;}
}
When try to add a new Person with many new PhoneNumbers using the following approach:
Person person = new Person {Name = "Jimmy"};
foreach(var phone in Phone_Number_In_Posted_Form){
person.PhoneNumbers.Add(new PhoneNumber {Number = phone});
}
Db.Entity<Person>(person).State = EntityState.Added;
Db.SaveChanges();
Entity framework does not automatically associate the Id (Auto Increment) generated to the PhoneNumbers (the navigational property) and for that reason the PhoneNumbers is not saved by SQL Server. Although this can be worked around through getting the generated Id and run another loop to associate it manually, I'd like to know if there is any standard solution built into Entity Framework that can work more effectively.

Answer 1

Entity framework does not automatically associate the Id (Auto Increment) generated to the PhoneNumbers (the navigational property) and for that reason the PhoneNumbers is not saved by SQL Server
The reason is different. It's because setting the State property does not cascade (does not apply recursively to the related data), hence is not a replacement of the corresponding DbContext / DbSet methods.
In you your case, instead of setting the State to Added you should call the Add method:
Person person = new Person {Name = "Jimmy"};
foreach(var phone in Phone_Number_In_Posted_Form){
person.PhoneNumbers.Add(new PhoneNumber {Number = phone});
}
Db.Add(person);
Db.SaveChanges();