asp.net core EF cascade delete error

Question

I have a succesion of 2 related tables, see below

public class HazardsLocation
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public string IdHL { get; set; }
    [Required]
    public string HazLocation { get; set; }
    public string OrgID { get; set; }
    public ICollection<HazardsCategory> HazardsCategories { get; set; }
}

public class HazardsCategory
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public string IdHCA { get; set; }
    [Required]
    public string HazCategory { get; set; }
    public string IdHL { get; set; }
    [ForeignKey("IdHL")]
    public HazardsLocation HazardsLocation { get; set; }
}

and relation in Context

modelBuilder.Entity<HazardsLocation>()
                .HasMany(a => a.HazardsCategories)
                .WithOne(a => a.HazardsLocation)
                .OnDelete(DeleteBehavior.Cascade);

            modelBuilder.Entity<HazardsCategory>()
                .HasMany(a => a.HazardsSources)
                .WithOne(a => a.HazardsCategory)
                .OnDelete(DeleteBehavior.Cascade);

but when I try to delete one item from the first table I get the following error

 

SqlException: The DELETE statement conflicted with the REFERENCE constraint "FK_HazardsCategories_HazardsLocations_IdHL". The conflict occurred in database "aspnet-RoSafety-53bc9b9d-9d6a-45d4-8429-2a2761773502", table "dbo.HazardsCategories", column 'IdHL'.

 

The delete procedure

public async Task<IActionResult> OnPostDeleteAsync(string idhl)
{
    if (idhl == null)
    {
        return NotFound();
    }
    var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
    var orgid = await _context.UsersData.Where(s => s.Id == userId).Select(s => s.OrgID).FirstOrDefaultAsync();

    var hazard = await _context.HazardsLocations.FindAsync(idhl);
    _context.HazardsLocations.Remove(hazard);
    _context.SaveChanges();

    return RedirectToPage("/HazId/HazLocation");
}