Access nested objects in C#

Question

I am trying to access specific properties from my object via Google Books API. The content is deserialized into two POCOs to access the nested object. I am stuck on is accessing the properties of volumeInfo to gather info like the title, author, images, etc.

//POCOs
public class GBAModel1
{
    public List<GBAModel2> items { get; set; }
}
public class GBAModel2
{
    public string id { get; set; }
    public string selfLink { get; set; }
    public Object volumeInfo { get; set; }

}

//REPOSITORY
public async Task<List<GBAModel2>> GetBooksFromApi()
{
    string testUrl = "https://www.googleapis.com/books/v1/volumes?q=jujutsu+kaisen+isbn=%229781974733767%22+inauthor=Gege";

    using (HttpResponseMessage response = await ApiHelper.ApiClient.GetAsync(testUrl))
    {
        if (response.IsSuccessStatusCode)
        {
            GBAModel1 results = await response.Content.ReadFromJsonAsync<GBAModel1>();

            return results.items;
        } else
        {
            throw new Exception(response.ReasonPhrase);
        }
    }
}

//CONTROLLER
[HttpGet("/booksApi")]
public async Task<IActionResult> GetBooks()
{
    var testResult= await _bookAction.GetBooksFromApi();
    var testAccess = testResult[0].volumeInfo;
    return Ok(testAccess);
}

//EXAMPLE JSON
{
  "kind": "books#volumes",
  "totalItems": 1,
  "items": [
    {
      "kind": "books#volume",
      "id": "cltJEAAAQBAJ",
      "etag": "cWfbxxKUP7w",
      "selfLink": "https://www.googleapis.com/books/v1/volumes/cltJEAAAQBAJ",
      "volumeInfo": {
        "title": "Jujutsu Kaisen, Vol. 17",
        "subtitle": "Perfect Preparation",
        "authors": [
          "Gege Akutami"
        ],
        "publisher": "VIZ Media LLC",
        "publishedDate": "2022-08-16",
        "description": "Hunted down by Okkotsu and on the brink of death, Itadori recalls a troubling family scene from his past. But why is the former form of Noritoshi Kamo there? As the sorcerers begin to take action toward suppressing the lethal culling game, Maki pays the Zen’in clan a visit... -- VIZ Media",
        "industryIdentifiers": [
          {
            "type": "ISBN_13",
            "identifier": "9781974733767"
          }
        ],
        "imageLinks": {
          "smallThumbnail": "http://books.google.com/books/content?id=cltJEAAAQBAJ&printsec=frontcover&img=1&zoom=5&edge=curl&source=gbs_api",
          "thumbnail": "http://books.google.com/books/content?id=cltJEAAAQBAJ&printsec=frontcover&img=1&zoom=1&edge=curl&source=gbs_api"
        },
        "language": "en",
      },
    }
  ]
}

I tried using a dot property like var testAccess = testResult[0].volumeInfo.title but gave me a CS1061:

'object' does not contain a definition for 'title' and no accessible extension method 'title' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?).

And also tried getting the title through methods:

var testAccess = testResult[0].volumeInfo;
var try2 = testAccess .GetType()
          .GetProperty("title")
          .GetValue(this, null);
return Ok(try2);

...but error was

Object reference not set to an instance of an object.

How can I properly access this object?

Answer 1

In C#, the most idiomatic way of addressing problems such as these is to define DTOs to contain the desired properties:

public class VolumeInfo
{
    public string title { get; set; }
    public string subtitle { get; set; }
    public List<string> authors { get; set; }
    public string publisher { get; set; }
    public string publishedDate { get; set; }
    public string description { get; set; }
    public List<IndustryIdentifier> industryIdentifiers { get; set; }
    public ImageLinks imageLinks { get; set; }
    public string language { get; set; }
}

and then update the volumeInfo property of GBAModel2:

public class GBAModel2
{
    public string id { get; set; }
    public string selfLink { get; set; }
    public VolumeInfo volumeInfo { get; set; }
}

Then you can write testResult.items[0].volumeInfo.title.

If you don't want to create all these DTOs, you can also work directly with the JSON AST.