How Can I Serialize and Deserialize Fields Using System.Text.Json?

System.Text.Json: Serialization and Deserialization Fields

In newer .NET versions, System.Text.Json.JsonSerializer is the preferred JSON serialization and deserialization method. However, it poses a challenge for classes containing field variables, as these are not supported by default.

The problem

In older versions of .NET, field variables could be included in the serialization/deserialization process. With the introduction of JsonSerializer, only attributes are supported, leading to the following issues:

using System.Text.Json;

public class Car
{
    public int Year { get; set; } // 正确序列化
    public string Model; // 未正确序列化（字段变量）
}

static void Problem()
{
    Car car = new Car()
    {
        Model = "Fit",
        Year = 2008,
    };
    string json = JsonSerializer.Serialize(car); // {"Year":2008}
    Car carDeserialized = JsonSerializer.Deserialize<Car>(json);

    Console.WriteLine(carDeserialized.Model); // null!
}

Solution

To solve this problem, two strategies exist:

1. .NET 5 and above

Starting in .NET 5, public fields can be serialized and deserialized via:

• Set JsonSerializerOptions.IncludeFields to true
• Add [JsonInclude] attributes to fields

Example:

using System.Text.Json;
using System.Text.Json.Serialization;

static void Main()
{
    var car = new Car { Model = "Fit", Year = 2008 };

    // 启用支持
    var options = new JsonSerializerOptions { IncludeFields = true };

    // 传递“options”
    var json = JsonSerializer.Serialize(car, options);

    // 传递“options”
    var carDeserialized = JsonSerializer.Deserialize<Car>(json, options);

    Console.WriteLine(carDeserialized.Model); // 输出 "Fit"
}

public class Car
{
    public int Year { get; set; }
    [JsonInclude]
    public string Model;
}

2. .NET Core 3.x

In .NET Core 3.x, field serialization is not supported. As a workaround, consider using a custom converter to achieve the desired behavior.

For more information and detailed documentation, please refer to the following resources:

• .NET documentation: System.Text.Json
• GitHub Issues: #34558 and #876

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