Add ValueKind property in System.Text.Json.Nodes.JsonNode class

[kingcean]

Background and Motivation

System.Text.Json.Node.JsonNode has provided a way to as JsonObject, JsonArray and JsonValue, but has no way to get its value kind directly.

Proposed API

namespace System.Text.Json.Nodes
{
    public abstract class JsonNode : IDynamicMetaObjectProvider {
+        public abstract JsonValueKind ValueKind { get; }
    }
}

Usage Examples

var json = JsonNode.Parse("{ \"name\": \"Kingcean\" }");
Assert.AreEqual(JsonValueKind.Object, json.ValueKind );
Assert.AreEqual(JsonValueKind.String, json["name"].ValueKind ;

Implementation for Reference

// namespace System.Text.Json.Nodes
public abstract class JsonNode
{
    public abstract JsonValueKind ValueKind { get; }
    // ...
}
public sealed class JsonArray : JsonNode, IList<JsonNode?>, ICollection<JsonNode?>, IEnumerable<JsonNode?>, IEnumerable
{
    public override JsonValueKind ValueKind => JsonValueKind.Array;
    // ...
}
public sealed class JsonObject : JsonNode, IDictionary<string, JsonNode?>, ICollection<KeyValuePair<string, JsonNode?>>, IEnumerable<KeyValuePair<string, JsonNode?>>, IEnumerable
{
    public override JsonValueKind ValueKind => JsonValueKind.Object;
    // ...
}
internal abstract partial class JsonValue<TValue> : JsonValue
{
    public override JsonValueKind ValueKind
    {
        get
        {
            if (_value is null) return JsonValueKind.Null;
            if (_value is JsonElement element) return element.ValueKind;
            if (_value is string || _value is Guid || _value is DateTime || _value is DateTimeOffset) return JsonValueKind.String;
            if (_value is bool b) return b ? JsonValueKind.True : JsonValueKind.False;
            if (_value is int || _value is long || _value is uint || _value is ulong || _value is short || _value is ushort || _value is double || _value is float || _value is decimal || _value is byte ||  || _value is sbyte) return JsonValueKind.Number;
            throw new NotSupportedException();
        }
    }
    // ...
}

[ghost]

Tagging subscribers to this area: @eiriktsarpalis, @layomia
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Background and Motivation

System.Text.Json.Node.JsonNode has provided a way to as JsonObject, JsonArray and JsonValue, but has no way to get its value kind directly.

Proposed API

namespace System.Text.Json.Nodes
{
    public abstract class JsonNode : IDynamicMetaObjectProvider {
+        public abstract JsonValueKind ValueKind { get; }
    }
}

Usage Examples

var json = JsonNode.Parse("{ \"name\": \"Kingcean\" }");
Assert.AreEqual(JsonValueKind.Object, json.ValueKind );
Assert.AreEqual(JsonValueKind.String, json["name"].ValueKind ;

Implementation for Reference

// namespace System.Text.Json.Nodes
public abstract class JsonNode
{
    public abstract JsonValueKind ValueKind { get; }
    // ...
}
public sealed class JsonArray : JsonNode, IList<JsonNode?>, ICollection<JsonNode?>, IEnumerable<JsonNode?>, IEnumerable
{
    public override JsonValueKind ValueKind => JsonValueKind.Array;
    // ...
}
public sealed class JsonObject : JsonNode, IDictionary<string, JsonNode?>, ICollection<KeyValuePair<string, JsonNode?>>, IEnumerable<KeyValuePair<string, JsonNode?>>, IEnumerable
{
    public override JsonValueKind ValueKind => JsonValueKind.Object;
    // ...
}
internal abstract partial class JsonValue<TValue> : JsonValue
{
    public override JsonValueKind ValueKind
    {
        get
        {
            if (_value is null) return JsonValueKind.Null;
            if (_value is JsonElement element) return element.ValueKind;
            if (_value is string || _value is Guid || _value is DateTime || _value is DateTimeOffset) return JsonValueKind.String;
            if (_value is bool b) return b ? JsonValueKind.True : JsonValueKind.False;
            if (_value is int || _value is long || _value is uint || _value is ulong || _value is short || _value is ushort || _value is double || _value is float || _value is decimal || _value is byte ||  || _value is sbyte) return JsonValueKind.Number;
            throw new NotSupportedException();
        }
    }
    // ...
}

Author:	kingcean
Assignees:	-
Labels:	api-suggestion, area-System.Text.Json, untriaged
Milestone:	-

[kevinchalet]

Having such a property would be extremely useful! 👏🏻

/cc @steveharter

[kevinchalet]

As mentioned in #52611, this property would be very useful in OpenIddict. Any chance it could be discussed for 6.0?

[steveharter]

The main reason that this isn't supported is that a JsonValue in "edit mode" can be assigned to any CLR type - a POCO, a Dictionary, an Enum, etc and in JSON they may be serialized in an arbitrary format depending on the converter. In "read mode" (after a Parse()) the underlying JsonElement.ValueKind can be used.

However, I did create a JsonNode extension sample for ValueKind in #55827 (comment) that handles this pretty well, but is not cheap when in "edit" mode and these types of values are assigned to a JsonValue. I plan on formalizing the sample soon (in STJ tests) and depending on feedback may make it into 7.0.

Also, note that JsonNode.GetValue<object>() can be called to get the underlying value. This may be useful in certain scenarios, like ValueKind, where inspection of the value is necessary. I'm also updating the doc to make this more clear.

Closing as it should be addressed by #55827.

[sebastienros]

Also, note that JsonNode.GetValue<object>() can be called to get the underlying value

Is it possible that it returns a JsonElement in some cases instead?

Update

Just assume I had not read the doc correctly ... thanks