Why does EF insert the same Guid Ids in different fileds? - asp.net-mvc

Question

I've a Page entity dependent on Investor entity as investor creates a page:
public class Page
{
[Required, DatabaseGenerated(DatabaseGeneratedOption.Identity), Key]
public Guid Id { get; set; }
[Required(ErrorMessage = "Describe the idea of your blog")]
public string Description { get; set; }
[Display(Name = "Тags")]
[Required(ErrorMessage = "Let people know what content you're going to share")]
public ICollection<Investor> Subscribers { get; set; }
public Guid AuthorId { get; set; }
public Investor Author { get; set; }
}
That's what in my dbContext:
modelBuilder.Entity<Page>()
.HasOne(b => b.Author)
.WithOne(u=> u.Page)
.HasForeignKey<Page>(b => b.AuthorId)
.OnDelete(DeleteBehavior.Restrict);
Here's the controller for creating a Page:
public class PageController : Controller
{
private readonly DataManager _dataManager;
private readonly UserManager<ApplicationUser> _userManager;
public PageController(UserManager<ApplicationUser> userManager, DataManager dataManager)
{
_userManager = userManager;
_dataManager = dataManager;
}
public IActionResult Create(Guid Id)
{
var investor = _dataManager.Investors.GetInvestorById(Id);
if (investor.Page != null)
{
return RedirectToPage("/Account/ProfileCheck", new { Id = investor.User.Id, area = "Identity"});
}
var page = new Page();
return View(page);
}
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult Create(Page page)
{
if (ModelState["Description"].Errors.Count() == 0)
{
var currentUserId = _userManager.GetUserId(HttpContext.User);
var investor = _dataManager.Investors.GetInvestorByUserId(currentUserId);
page.Author = investor;
_dataManager.Pages.SavePage(page);
return RedirectToPage("/Account/ProfileCheck", new { Id = investor.User.Id, area = "Identity" });
}
return View(page);
}
}
However, In HttpPost Action that page has an Id and this Id equals to author's Id who created it.
This's the view for Create action
#model FinicWebApp.Domain.Entitites.Page
<form method="post" asp-action="Create">
<div class="border p-3">
<div asp-validation-summary="ModelOnly" class="text-danger" ></div>
<div class="form-group row">
<h2 class="text-black-50 pl-3">Create Page</h2>
</div>
<div class="row">
<div class="col-12">
<div class="form-group row">
<div class="col-6">
<label asp-for="Description"></label>
</div>
</div>
<div class="form-group row">
<div class="col-4">
<input asp-for="Description" class="form-control" />
<span asp-validation-for="Description" class="text-danger"></span>
</div>
</div>
<div class="form-group row">
<div class="col-8 text-center row">
<div class="col">
<input type="submit" class="btn btn-info w-75" value="Create"/>
</div>
</div>
</div>
</div>
</div>
</div>
</form>
In my db all the pages' ids equal to investors' ids who created them. But I need pages' ids to be different. How can I get it?