How to do a cascade delete in .Netcore 2.0

Question

In my application, I have this class structure.

public class Class1
{
    public long Class1ID { get; set; }
    public ICollection<Class2> class2 { get; set; }
}

public class Class2
{
    public long Class2ID { get; set; }
    public ICollection<Link> Link { get; set; }
}

public class Link
{
    public long ID { get; set; }

    public string URL { get; set; }
}

Front end:

public async Task<IActionResult> OnPostAsync(long? id)
{
    var r = 1 + 1;
    if (id == null)
    {
        return NotFound();
    }

    var Class1 = await _context.Class1.FindAsync(id);
    await _context.SaveChangesAsync();

    if (Class1 != null)
    {
        _context.Class1.Remove(Class1);
        await _context.SaveChangesAsync();
    }

    return RedirectToPage("./Index");
}

The data is data-bound correctly using a local db. I am able to edit and view Class1 right now. When I try to delete an instance of Class1 it says I can't because it is being used.

SqlException: The DELETE statement conflicted with the REFERENCE constraint "FK_Class2_Class1_Class1ID". The conflict occurred in database "DBName", table "dbo.Class2", column 'Class1ID'. The statement has been terminated.

In order to do a cascade delete, do I have to go through the database and delete all the related fields in the OnPostAsync() method? Or is there a much simpler way?