Linking a third model in EF CORE - entity-framework

Question

This is the EF CORE setup I have at the moment.
Telephone model
[ForeignKey("TelNoTypeID")]
public int? TelNoTypeID { get; set; }
public DropDown TelNoType { get; set; }
Person model
public ICollection<Telephone> TelephoneIDs { get; set; }
I've also tried using
public virtual ICollection<Telephone> TelephoneIDs { get; set; }
DropDown model
public int DropDownID { get; set; }
public string DisplayText { get; set; }
Person controller
public async Task<IActionResult> Details(int? id)
{
var person = await _context.Persons
.Include(p => p.Gender)
.Include(p => p.Title)
.Include(p => p.AddressIDs)
.Include(p => p.TelephoneIDs)
.SingleOrDefaultAsync(m => m.PersonID == id);
So a collection of Telephone numbers are stored against the Person model.
This brings back from the database and displays on the screen the numeric value from the field
Telephones.TelNoTypeID
The equivalent SQL to what I have is
select Telephones.TelNoTypeID from Person
inner join Telephones on Telephones.PersonID = Person.PersonID
I need to display the linked text value instead which is stored in
DropDown.displaytext
The equivalent SQL to what I need is
select DropDown.displaytext from Person
inner join Telephones on Telephones.PersonID = Person.PersonID
inner join DropDown on DropDown.DropDownID = Telephones.TelNoTypeID
I've tried using
.ThenInclude(p => p.<something>)
but the Dot notation just refers to the generic collection properties/methods, not back to my person, dropdown or telephone models
I've linked the Person model directly to the Dropdown model using and displaying the dropdown.displaytext with
Person model
[ForeignKey("GenderID")]
public int? GenderID { get; set; }
public virtual DropDown Gender { get; set; }
but despite putting the same code into telephone, it's not working
How can I link a third model (DropDown) to a second model (Telephone)?
Thanks

Answer 1

I was trying to link to the DropDown model, turns out I needed to link to the property, so
var person = await _context.Persons
.Include(p => p.Gender)
.Include(p => p.Title)
.Include(p => p.AddressIDs)
.Include(p => p.TelephoneIDs)
.ThenInclude(p => p.TelNoType)
//.Include("TelephoneIDs.TelNoType.DisplayText")
.SingleOrDefaultAsync(m => m.PersonID == id);
I don't understand why, I'm presuming it's because the links already exist between the 3 models and the ThenInclude points to the exact property I'm trying to link with/to.