Duplicate Foreign Key entries being created on insert - EF Core and Web Api 3.1 - asp.net-core

Question

I am currently learning how to work with EF Core with a simple one to many setup, where a user can have many items. In terms of retrieving the data from the tables, this is fine with some DTO models; however, when I try and add a user with multiple items via Postman, I noticed that for each item it had duplicated the user that many times (i.e. a user with 3 items will create 3 items and 3 users):
Postman (POST)
{
"username": "xxx",
"dob": "xxx",
"location": "xxx",
"items":[{
"item": "xxx",
"category": "xxx",
"type": "xxx"
},
{
"item": "xxx",
"category": "xxx",
"type": "xxx"
},
{
"item": "xxx",
"category": "xxx",
"type": "xxx"
}]
}
Context:
namespace TestWebApplication.Database
{
public class MyContext : DbContext
{
public DbSet<User> Users { get; set; }
public DbSet<Items> Items { get; set; }
public MyContext(DbContextOptions<MyContext> options)
: base(options)
{
// erm, nothing here
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<User>()
.HasMany(i => i.Items)
.WithOne(u => u.User);
}
public override int SaveChanges()
{
var entities = from e in ChangeTracker.Entries()
where e.State == EntityState.Added
|| e.State == EntityState.Modified
select e.Entity;
foreach (var entity in entities)
{
var validationContext = new ValidationContext(entity);
Validator.ValidateObject(entity, validationContext);
}
return base.SaveChanges();
}
}
}
Controller:
[HttpPost]
[Route("insertuseranditems")]
public ActionResult InsertUserAndItems(User user)
{
if (ModelState.IsValid)
{
using (MyContext myContext = _myContext as MyContext)
{
myContext?.Users?.Add(user);
int changes = myContext.SaveChanges();
if (changes > 0)
{
return Created("User saved", user);
}
}
}
return Accepted();
}
Items:
namespace TestWebApplication.Database
{
public class Items
{
[Key]
public int ItemId { get; set; }
public string Item { get; set; }
public string Category { get; set; }
public string Type { get; set; }
public virtual User User { get; set; }
}
}
Users:
namespace TestWebApplication.Database
{
public class User
{
[Key]
public int UserId { get; set; }
public string UserName { get; set; }
public string Dob { get; set; }
public string Location { get; set; }
public ICollection<Items> Items { get; set; }
}
}

Answer 1

I revisited my code and changed my Items.cs model to:
namespace TestWebApplication.Database
{
public class Items
{
[Key]
public int ItemId { get; set; }
public string Item { get; set; }
public string Category { get; set; }
public string Type { get; set; }
[ForeignKey("User")] // added this
public int? UserId { get; set; } // added this
public virtual User User { get; set; }
}
}
Now, when I send the above json via Postman, I get multiple items with the same user as a Foreign Key.
The site below seemed to help:
The ForeignKey Attribute