Restructuring a JSON object in C#

Question

I have some JSON data that looks like this:

[
  {
    "name": "foo",
    "id": 1,
    "child": {
          name: "A",
          id: 1,
     }
  },
  {
    "name": "bar",
    "id": 1,
    "child": {
          name: "A",
          id: 1,
     }
  },
  {
    "name": "baz",
    "id": 2,
    "child": {
          name: "B",
          id: 2,
     }
  },
  {
    "name": "alpha",
    "id": 1,
    "child": {
          name: "A",
          id: 1,
     }
  }
]

I'm loading it into my .NET project and trying to restructure it so that it returns a response that looks something like this:

[
  {
    "name": "A"
    "id": 1,
    "parents": [
        {
          "name": "foo",
          "id": 1,
        },
        {
           "name": "bar",
           "id": 1,
        },
        {
           "name": "alpha",
           "id": 1,
        }
     ]
  },
  {
    "name": "B"
    "id": 2,
    "parents": [
        {
          "name": "baz",
          "id": 2,
        }
     ]
  }
]

I was able to use LINQ to grab all the IDs that matched, but only for 1 ID.

var test = deserializedJsonData.Where(w => w.child.id == SomeID).Select(s => s).ToList()

The moment I tried to iterate "SomeID" inside of a loop to iterate it, it freezes and crashes.

Is there a more efficient way of doing this?

EDIT: Corrected typo as pointed out in comments

Don't you mean [{"name": "A", ..."parents": [...? foo is not a child of A in your input. — Xerillio
– Xerillio, Commented Mar 15, 2021 at 20:41
from d in deserializedJsonData group new { d.id, d.name } by new { d.child.id, d.child.name } into g select new { g.Key.name, g.Key.id, parents = g.AsEnumerable() }; — Aluan Haddad
– Aluan Haddad, Commented Mar 15, 2021 at 20:46
How are you deserializing the JSON? json.net? system.text.json? Something else? To what data model or document object model are you deserializing? And is the JSON schema fixed, or might there be additional properties? The moment I tried to iterate "SomeID" inside of a loop to iterate it, it freezes and crashes. -- then can you please edit your question to share a minimal reproducible example that reproduces the problem? — dbc
– dbc, Commented Mar 15, 2021 at 21:39

Zunayed Shahriar · Accepted Answer · 2021-03-16 12:16:19Z

Regarding your requirement, I've created the objects.

public class Base
{
    public int id { get; set; }
    public string name { get; set; }
}

public class Data : Base
{
    public Base child { get; set; }
}

public class RequiredData : Base
{
    public List<Base> parents { get; set; }
}

Then created a comparer to distinct your child objects.

public class BaseComparer : IEqualityComparer<Base>
{
    public bool Equals(Base x, Base y)
    {
        if (x.id.Equals(y.id) && (x.name.Equals(y.name)))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    public int GetHashCode(Base obj)
    {
        unchecked
        {
            int hash = 100;
            hash = hash * 10 + obj.id.GetHashCode();
            hash = hash * 10 + obj.name.GetHashCode();
            return hash;
        }
    }
}

Finally,

string rawData = File.ReadAllText(@"your_json_file_path");
var parsedData = JsonConvert.DeserializeObject<Data[]>(rawData);
var childs = parsedData.GroupBy(g => g.child.id).Select(s => new Base()
{
    id = s.Key,
    name = s.Where(w => w.child.id == s.Key).First().child.name
}).ToList();
var result = parsedData.GroupBy(s => s.child).Select(s => 
new RequiredData()
{
    id = s.Key.id,
    name = s.Key.name,
    parents = parsedData.Where(w => w.child.id == s.Key.id).Select(x =>
    new Base()
    {
        id = x.id,
        name = x.name
    }).ToList()
}).Distinct(new BaseComparer()).ToList();
var jsonResult = JsonConvert.SerializeObject(result);

jsonResult will contain your required output.

Note: I'm using Newtonsoft.Json library for JSON operations.

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