How to get parent node id from child node id in JSON

Question

Here is my JSON string:

[
  {
    "Order": 1,
    "IssueId": 83719,
    "Journal": "HLRF",
    "Identity": "HLRF, Vol.137, Iss.4, y.2024, February 2024",
    "Web": "https://harvardlawreview.org/forum/issue/83719",
    "Articles": [
      {
        "Link": "https://harvardlawreview.org/forum/article/1451533",
        "Pdf": 3789188
      },
      {
        "Link": "https://harvardlawreview.org/forum/article/1451561",
        "Pdf": 3789306
      },
      {
        "Link": "https://harvardlawreview.org/forum/article/1451574",
        "Pdf": 3789358
      }
    ]
  }
]

And I am using Json.Net and object structure like this:

var issues = JsonConvert.DeserializeObject<List<Issue>>("___Json.String___");

public class Issue
{
    public int Order { get; set; }
    public int IssueId { get; set; }
    public string Journal { get; set; }
    public string Identity { get; set; }
    public string Web { get; set; }
    public List<Article> Articles { get; set; }
}

public class Article
{
    public string Link { get; set; }
    public int Pdf { get; set; }
} 

From the JSON, I know the Pdf number like 3789306. It is located in the first issue and the second article.

So I want to get the parent issue's id: IssueId. In our example 83719. But I did not manage it.

Answer 1

As you deserialize into List<Issue>, this will be easier to achieve via System.Linq to search the parent that contains the children with Pdf is 3789306.

For the handling in case that articleId may not exist, use .FirstOrDefault() and null-conditional operator (?.).

using System.Linq;

int articleId = 3789306;
int? issueId = issues.FirstOrDefault(x => x.Articles.Any(y => y.Pdf == articleId))
    ?.IssueId;

Answer 2

So I want to get parent issue's id IssueId. In our example 83719. But I did not manage it.

This can be achieved by using Linq query. First of all you need to flattens the structure using SelectMany to access all articles across issues. Then, need to filters for the article with the matching Pdf and selects the IssueId from its parent.

Finally, it retrieves the first matching element or indicates if no article was found.

int? parentId = issues!.Select((issue, index) => new { issue, index })
                           .Where(x => x.issue.Articles.Any(a => a.Pdf == pdfToFind))
                           .Select(x => x.issue.IssueId)
                           .FirstOrDefault();

Full Demo:

[HttpGet]
[Route("GetParentNode")]
public IActionResult GetParentNode()
{
    string json = @"
[
  {
    ""Order"": 1,
    ""IssueId"": 83719,
    ""Journal"": ""HLRF"",
    ""Identity"": ""HLRF, Vol.137, Iss.4, y.2024, February 2024"",
    ""Web"": ""https://harvardlawreview.org/forum/issue/83719"",
    ""Articles"": [
      {
        ""Link"": ""https://harvardlawreview.org/forum/article/1451533"",
        ""Pdf"": 3789188
      },
      {
        ""Link"": ""https://harvardlawreview.org/forum/article/1451561"",
        ""Pdf"": 3789306
      },
      {
        ""Link"": ""https://harvardlawreview.org/forum/article/1451574"",
        ""Pdf"": 3789358
      }
    ]
  }
]";

    var issues = JsonConvert.DeserializeObject<List<Issue>>(json);

    int pdfToFind = 3789306;

   
    int? parentId = issues!.Select((issue, index) => new { issue, index })
                          .Where(x => x.issue.Articles.Any(a => a.Pdf == pdfToFind))
                          .Select(x => x.issue.IssueId)
                          .FirstOrDefault();

   
    return Ok("Parent Issue's Id: " + parentId);
}

Output:

Note: For more linq techniques, pleaes refer to this official document.