I have been struggling with foreign key things in my project but to make my point clear, I am going to give you the official tutorial for the relationship things in ASP.NET.

I have created these two models in this page.

// Principal (parent)
public class Blog
{
    public int Id { get; set; }
    public ICollection<Post> Posts { get; } = new List<Post>(); // Collection navigation containing dependents
}

// Dependent (child)
public class Post
{
    public int Id { get; set; }
    public int BlogId { get; set; } // Required foreign key property
    public Blog Blog { get; set; } = null!; // Required reference navigation to principal
} 

They are our models. After creating these models in Models folder, I have created their corresponding controllers. Then, I have added this to my Context script in Data folder:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>()
        .HasMany(e => e.Posts)
        .WithOne(e => e.Blog)
        .HasForeignKey(e => e.BlogId)
        .IsRequired();
}

Finally, I have typed add-migration and update-database, everything worked fine. Then I have created a Blog in /Blogs/Create. It is successfully done. But when I tried to add a new Post, I have got nothing, the page is just reloaded with nothing done.I have added some breakpoints to the create function in PostsController and saw that ModelState is invalid.

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("Id,BlogId")] Post post)
{

    if (ModelState.IsValid)
    {
        _context.Add(post);
        await _context.SaveChangesAsync();
        return RedirectToAction(nameof(Index));
    }
    ViewData["BlogId"] = new SelectList(_context.Set<Blog>(), "Id", "Id", post.BlogId);
    return View(post);

}

ModelState remains still invalid. It makes sense since we are not pushing anything to this function as a parameter from the Create.cshtml. But I don’t get how I should handle this problem.
I am using .Net 8.

When I delete the ModelState check, I got no error. But I don’t know if this is a solid solution.