Convert object to System.Text.Json.JsonElement

In .NET 6 methods are being added to JsonSerializer to serialize an object directly to a JsonElement or JsonDocument:

public static partial class JsonSerializer
{
    public static JsonDocument SerializeToDocument<TValue>(TValue value, JsonSerializerOptions? options = null);
    public static JsonDocument SerializeToDocument(object? value, Type inputType, JsonSerializerOptions? options = null);
    public static JsonDocument SerializeToDocument<TValue>(TValue value, JsonTypeInfo<TValue> jsonTypeInfo);
    public static JsonDocument SerializeToDocument(object? value, Type inputType, JsonSerializerContext context);

    public static JsonElement SerializeToElement<TValue>(TValue value, JsonSerializerOptions? options = null);
    public static JsonElement SerializeToElement(object? value, Type inputType, JsonSerializerOptions? options = null);
    public static JsonElement SerializeToElement<TValue>(TValue value, JsonTypeInfo<TValue> jsonTypeInfo);
    public static JsonElement SerializeToElement(object? value, Type inputType, JsonSerializerContext context);
}

Thus in .NET 6 you will be able to do:

using var jsonDocument = JsonSerializer.SerializeToDocument(new MyClass { Data = "value" });

or

var jsonElement = JsonSerializer.SerializeToElement(new MyClass { Data = "value" });

Notes:

• JsonSerializerContext and JsonTypeInfo<T> are newly exposed in .NET 6 and provide metadata about a set of types, or a single type T, that is relevant to JSON serialization. They are used when serializing using metadata and code generated at compile time. See Try the new System.Text.Json source generator for details.

• JsonDocument is IDisposable, and in fact must needs be disposed because, according to the docs:

  JsonDocument builds an in-memory view of the data into a pooled buffer. Therefore, unlike JObject or JArray from Newtonsoft.Json, the JsonDocument type implements IDisposable and needs to be used inside a using block.

  In your sample code you do not dispose of the document returned by JsonDocument.Parse(), but you should.

• The new methods should be present in .NET 6 RC1.

In .NET 5 and earlier a method equivalent to JObject.FromObject() is not currently available out of the box in System.Text.Json. There is an open enhancement about this, currently targeted for Future:

• We should be able serialize and serialize from DOM #31274.

In the interim you may get better performance by serializing to an intermediate byte array rather than to a string, since both JsonDocument and Utf8JsonReader work directly with byte spans rather than strings or char spans, like so:

public static partial class JsonExtensions
{
    public static JsonDocument JsonDocumentFromObject<TValue>(TValue value, JsonSerializerOptions options = default) 
        => JsonDocumentFromObject(value, typeof(TValue), options);

    public static JsonDocument JsonDocumentFromObject(object value, Type type, JsonSerializerOptions options = default)
    {
        var bytes = JsonSerializer.SerializeToUtf8Bytes(value, type, options);
        return JsonDocument.Parse(bytes);
    }

    public static JsonElement JsonElementFromObject<TValue>(TValue value, JsonSerializerOptions options = default)
        => JsonElementFromObject(value, typeof(TValue), options);

    public static JsonElement JsonElementFromObject(object value, Type type, JsonSerializerOptions options = default)
    {
        using var doc = JsonDocumentFromObject(value, type, options);
        return doc.RootElement.Clone();
    }
}

And then call it like:

using var doc = JsonExtensions.JsonDocumentFromObject(new MyClass { Data = "value" });

Or, if you need to use the root element outside the scope of a using statement:

var element = JsonExtensions.JsonElementFromObject(new MyClass { Data = "value" });

Notes:

• As noted above, a JsonDocument needs to be disposed after being created. The above JsonExtensions.JsonElementFromObject() extension methods correctly dispose of their internal document and returns a clone of the root element, as recommended in the documentation.

• Serializing to an intermediate Utf8 byte sequence is likely to be more performant than serializing to a string because, according to the docs:

  Serializing to UTF-8 is about 5-10% faster than using the string-based methods. The difference is because the bytes (as UTF-8) don't need to be converted to strings (UTF-16).

• For the inverse method, see System.Text.Json.JsonElement ToObject workaround.

Demo fiddle here.

dbc's answer is a good start, but not enough if the object value is already a json string! Moreover, the type is not used in his code.

Thus I propose the following improved version:

    public static JsonDocument JsonDocumentFromObject(object value, JsonSerializerOptions options = null)
    {
        if (value is string valueStr)
        {
            try { return JsonDocument.Parse(valueStr); }
            catch {}
        }

        byte[] bytes = JsonSerializer.SerializeToUtf8Bytes(value, options);
        return JsonDocument.Parse(bytes);
    }

    public static JsonElement JsonElementFromObject(object value, JsonSerializerOptions options = null)
    {
        JsonElement result;
        using (JsonDocument doc = JsonDocumentFromObject(value, options))
        {
            result = doc.RootElement.Clone();
        }
        return result;
    }

with the following unit test (xUnit):

    [Fact()]
    public void JsonElementFromObjectTest()
    {
        object o = new
        {
            id = "myId",
            timestamp = DateTime.UtcNow,
            valid = true,
            seq = 1
        };

        JsonElement element1 = JsonSerializerExtension.JsonElementFromObject(o);
        Assert.Equal(JsonValueKind.Object, element1.ValueKind);
        string oStr1 = element1.GetRawText();
        Assert.NotNull(oStr1);

        JsonElement element2 = JsonSerializerExtension.JsonElementFromObject(oStr1);
        Assert.Equal(JsonValueKind.Object, element2.ValueKind);
        string oStr2 = element2.GetRawText();
        Assert.NotNull(oStr2);

        Assert.Equal(oStr1, oStr2);
    }

without the direct try Parse, element2 is a JsonValueKind.String and oStr2 contains the not escaped unicode characters, thus being an invalid Json string.

A slick approach in .NET 5 would be:

private JsonElement JsonElementFromObject(object value)
{
    var jsonUtf8Bytes = JsonSerializer.SerializeToUtf8Bytes(value, new JsonSerializerOptions());
    using var doc = JsonDocument.Parse(jsonUtf8Bytes);
    return doc.RootElement.Clone();
}

Steps:

1. Convert the value into a JSON string, encoded as UTF-8 bytes (SerializeToUtf8Bytes).
2. Parse the JSON string (JsonDocument.Parse).
3. Return the root element.