Create Newtonsoft.Json.Linq.JArray from another array with different structure

Question

I have first Newtonsoft.Json.Linq.JArray with this structure:

[
  {
    "Fields": [
      {
        "Value": "child",
        "Key": "Relationship"
      },
      {
        "Value": "Alex",
        "Key": "FirstName"
      }
    ]
  }
]

And another Newtonsoft.Json.Linq.JArray:

[
  {
    "Relationship": "child",
    "FirstName": "Alex"
  }
]

Is it real to turn second one to the first one? Have not much experience in c# and Linq.

Answer 1

To transform your first JSON sample to your second, you may use LINQ to JSON as follows:

// Parse (or load from a stream) the incoming JSON as a JArray
var array = JArray.Parse(jsonString);

// For each object in the array, query they Key/Value properties of each Fields[*] object and turn then into a single JPropery, 
// then add those properties to a new JObject
var query = array.Select(i => 
    new JObject(i.SelectTokens("Fields[*]").Select(o => new JProperty((string)o["Key"], o["Value"]))));

// Create a new JArray from the query
var newArray = new JArray(query);

The trickest part is here:

i => new JObject(i.SelectTokens("Fields[*]").Select(o => 
    new JProperty((string)o["Key"], o["Value"])))

This expression:

1. Uses SelectTokens() to query all Fields[*] objects in the root array item;
2. then gets the "Key" and "Value" properties of each object;
3. then turns them into a single JProperty;
4. and finally combines the JProperty instances into a single JObject.

Note that, if one of the [*].Fields[*].Key properties is missing, the code above will throw an exception, so you might want to check for that.

Demo fiddle #1 here.

Similarly, to transform your second sample to your first, you can do:

var query = array
    .OfType<JObject>()
    .Select(o => 
           new JObject
           {
               {"Fields", new JArray(o.Properties().Select(p => new JObject{{"Key", p.Name}, {"Value", p.Value}}))},
           });

var newArray = new JArray(query);

Here I am using C#'s dictionary collection initializer syntax to initialize my JObject instances, which I can do because JObject implements IDictionary<string, JToken>.

Demo fiddle #2 here.