I need help in converting following code which is using newtonsoft to System.Text.Json

string myList = null!;
string jSon = /* From some source */;
object jsonObject = JsonConvert.DeserializeObject(jSon, typeof(object));

// Loop through the keys
foreach (var jsonList in ((Newtonsoft.Json.Linq.JObject)(jsonObject)))
{                   
    if (jsonList.Key == "myKey")
    {                       
        foreach (object o in (jsonList.Value.ToArray()))
        {                           
            myList  = o.ToString().ToUpper()   ',';
        }
    }
}

json like:

{"myKey":["fir","dsdsd"],"status":"ok"}

CodePudding user response：

With System.Text.Json, you can parse arbitrary JSON using either the JsonDocument or JsonNode document object models. The differences are:

• JsonNode is modifiable and is, in my opinion, easier to work with as it most closely resembles Newtonsoft's LINQ to JSON model. It was added in .NET 6.
• JsonDocument is read-only, but may be a little more memory-efficient in parsing huge JSON files. It was introduced as part of the original System.Text.Json API in .NET Core 3.0.

Thus, using JsonNode, your code can be rewritten as follows:

static string QueryJson(string json, string myKey, bool addComma = false)
{
    // Parse to a JsonNode and cast to JsonObject.  An exception is thrown if not an object
    var node = JsonNode.Parse(json)!.AsObject(); 
    
    // Query the array of strings
    var query = (node[myKey] as JsonArray)?.Select(i => i?.ToString().ToUpper()) ?? Enumerable.Empty<string>();
    if (addComma)
        query = query.Concat(new [] { "" });

    // Join the string array into a single comma-separated string
    var myString = string.Join(',', query);

    return myString;
}

And here is a version of the same logic using JsonDocument:

static string QueryJsonWithJsonDocument(string json, string myKey, bool addComma = false)
{
    // Parse to a JsonNode and cast to JsonObject.  An exception is thrown if not an object
    using var doc = JsonDocument.Parse(json);

    // Query the array of strings
    var query = doc.RootElement.GetProperty(myKey).EnumerateArray().Select(e => e.GetString()?.ToUpper());
    if (addComma)
        query = query.Concat(new [] { "" });

    // Join the string array into a single comma-separated string
    var myString = string.Join(',', query);

    return myString;
}

Notes:

• You tagged your question .net-core-3.1. This version goes out of support in about a month, on December 13, 2022. If you are using this version you will need to use JsonDocument since JsonNode was introduced in .NET 6.

• JsonDocument is disposable, and should be disposed to ensure that pooled memory is returned to the system. JsonNode is not disposable.

• It will be more efficient to use string.Join() than manually building a comma-separated string using multiple string additions.

• Your current code adds a trailing comma to the string: FIR,DSDSD,. This looks like a bug, but if you want that you can make string.Join() add a trailing comma by adding an extra empty string to the query.

Demo fiddle here.