How to load XML data to a data structure?

Question

I have the following XML document

<?xml version = "1.0" encoding = "utf-8"?>
<flights_for_sale>
<ad id="0001" createdon ="11/02/20" expireson="12/02/20">
<aircraft id="A10">
<year> 1977 </year>
<make> <![CDATA[&c;]]> </make>
<model> Skyhawk </model>
<color> Light blue and white </color>
<description>
New paint, nearly new interior,
685 hours SMOH, full IFR King avionics
</description>
<price> 23,495 </price>
</aircraft>
<seller id = "s001" phone="123-123-123"> Skyway Aircraft </seller>
<seller id = "s002" phone="123-123-222"> Boeing </seller>
<seller id = "s003" phone="123-123-233"> McDouglas </seller>
<membership id="1000" from="12/03/16" to="12/03/18" no="M0001">Silver</membership>
<membership id="1000" from="12/03/16" to="12/03/18" no="M0002">Gold</membership>
<membership id="1000" from="12/03/16" to="12/03/18" no="M0003">Platinum</membership>
<location>
<city> Rapid City, </city>
<state> South Dakota </state>
</location>
</ad>
<ad id="002" createdon ="11/05/20" expireson="12/05/20">
<aircraft>
<year> 1965 </year>
<make> &p; </make>
<model> Cherokee </model>
<color> Gold </color>
<description>
240 hours SMOH, dual NAVCOMs, DME,
new Cleveland brakes, great shape
</description>
</aircraft>
<seller phone="555-333-2222" email="[e-mail]" id="s004">John Seller</seller>
<membership id="1000" from="12/03/16" to="12/03/18" no="M0020">State Membership</membership>
<membership id="1000" from="12/03/16" to="12/03/18" no="M0002">Gold</membership>
<location>
<city> St. Joseph, </city>
<state> Missouri </state>
</location>
</ad>
</flights_for_sale>

I have the following C# classes

class Advert2
{
public int? Id { get; set; }
public DateTime? CreatedOn { get; set; }
public DateTime? ExpiresOn { get; set; }
public Aircraft MyAircraft { get; set; }
public List<Seller2> MySellers { get; set; }
public List<Membership> MyMemberships { get; set; }

public Advert2()
{
MySellers = new List<Seller2>();
MyMemberships = new List<Membership>();
MyAircraft = new Aircraft();
}


}

class Seller2
{
public int? Id { get; set; }
public string SellerName { get; set; }
public string Phone { get; set; }
}

class Membership
{
public int? Id { get; set; }
public string MembershipNumber { get; set; }

public DateTime? From { get; set; }

public DateTime? To { get; set; }

public String MemberType { get; set; }

}

class Aircraft {

public string Make { get; set; }
public string Model { get; set; }


public decimal? Price { get; set; }

public string Description { get; set; }
}

Then i have used the following two methods to parse XML elements and attributes ( check for NULLs )

public static class XMLCommons
{
public static string TryGetElementValue(this XElement parentEl, string elementName, string defaultValue = null)
{
var foundEl = parentEl.Element(elementName);

if (foundEl != null)
{
return foundEl.Value;
}

return defaultValue;
}



public static string TryGetAttribtueValue(this XElement parentEl, string elementName, string attrName, string defaultValue = null)
{
var foundEl = parentEl.Element(elementName);

if (foundEl != null) {
//check attribute exists

var foundAttr = foundEl.Attribute(attrName);
if (foundAttr != null)
{
return foundAttr.Value;
}
}

return defaultValue;
}


}

 

Then i have written the following code to read element/attributes on the XML, and populate data to the `Advert2` object structure

var xmlPath2 = System.IO.Path.Combine("../../../data/" + "XMLFile2.xml");
var xml2 = XDocument.Load(xmlPath2);
var query2 = xml2.Root.Descendants("ad").Select(n => new Advert2 {
Id = Convert.ToInt32(n.Parent.TryGetAttribtueValue("ad", "id")),
CreatedOn = Convert.ToDateTime( n.Parent.TryGetAttribtueValue("ad", "createdon") ),
ExpiresOn = Convert.ToDateTime(n.Parent.TryGetAttribtueValue("ad", "expireson")),
MyAircraft = new Aircraft {
Make = n.TryGetElementValue("make"),
Model = n.TryGetElementValue("model"),
Description = n.TryGetElementValue("description"),
Price = Convert.ToDecimal( n.TryGetElementValue("price") ) },
MySellers = new List<Seller2>().Add( new Seller2 {
Id = Convert.ToInt32( n.TryGetAttribtueValue("seller","id") ),
SellerName = n.TryGetElementValue("seller"),
Phone = n.TryGetAttribtueValue("seller","phone")
} )
}).ToList();

but the issues is i get syntax errors when i tried to create objects to populate `MySellers` List.

Error:

Severity    Code    Description Project File    Line    Suppression State
Error   CS0029  Cannot implicitly convert type 'void' to System.Collections.Generic.List<XMLParsing.Seller2>'

So it seems like i don't know how to populate those two collections `MySellers` and `MyMemberships`.

is there away to populate those two collections so i can create the `Averts2` Collection?