使用 System.Text.Json 创建 JSON 对象

Question

I am working on migrating from Json.Net to System.Text.Json. I am not sure how we can build json object like below code using System.Text.Json. I tried lots of workaround but nothing seems working. I know we can do this using JsonObject from Dot net 6 , but I am using Dot net core 5.

Newtonsoft code:

var json = new JObject(
    new JProperty("Status", result.Status.ToString()),
    new JProperty("Duration", result.TotalDuration.TotalSeconds.ToString()));
if (result.Entries.Any())
{
    var entries = new JObject(result.Entries
        .Select(d => new JProperty(d.Key, new JObject(new JProperty("Status", d.Value.Status.ToString()), new JProperty("Duration", d.Value.Duration.TotalSeconds.ToString()), new JProperty("Description", d.Value.Description)))));

    json.Add(new JProperty("result", entries));
}

Answer 1

In .NET 5 you can use a combination of dictionaries and anonymous types to construct free-form JSON on the fly. For instance, your sample code can be rewritten for System.Text.Json as follows:

var json = new Dictionary<string, object>
{
    ["Status"] = result.Status.ToString(),
    ["Duration"] = result.TotalDuration.TotalSeconds.ToString(NumberFormatInfo.InvariantInfo),
};

var entries = result.Entries.ToDictionary(
    d => d.Key,
    d => new { Status = d.Value.Status.ToString(), Duration = d.Value.Duration.TotalSeconds.ToString(NumberFormatInfo.InvariantInfo), Description = d.Value.Description } );
if (entries.Count > 0)
    json.Add("result", entries);

var newJson = JsonSerializer.Serialize(json, new JsonSerializerOptions { WriteIndented = true });

Notes:

• When constructing a JSON object with properties whose values have mixed types (like the root json object in your example) use Dictionary<string, object> (or ExpandoObject , which implements Dictionary<string, object> ).

  You must use object for the value type because System.Text.Json does not support polymorphism by default unless the declared type of the polymorphic value is object . For confirmation, see How to serialize properties of derived classes with System.Text.Json :

  You can get polymorphic serialization for lower-level objects if you define them as type object .

• When constructing a JSON object with a fixed, known set of properties, use an anonymous type object.

• When constructing a JSON object with runtime property names but fixed value types, use a typed dictionary. Oftentimes LINQ's ToDictionary() method will fit perfectly, as is shown above.

• Similarly, when constructing a JSON array with values that have mixed types, use List<object> or object [] . A typed List<T> or T [] may be used when all values have the same type.

• When manually formatting numbers or dates as strings, be sure to do so in the invariant locale to prevent locale-specific differences in your JSON.

Demo fiddle here .