c# - 在不更改模型类的情况下，为 Json.NET 中的一个属性自定义序列化程序

Question

我需要做类似下面的事情，但我需要在不添加属性或以其他方式污染模型类的情况下进行。理想的解决方案是通过 JsonSerializerSettings 工作，而不会干扰其他自定义序列化。顺便说一句，以下来自这个问题:Custom conversion of specific objects in JSON.NET

public class Person
{
    public string FirstName { get; set; }
    [JsonConverter(typeof(AllCapsConverter))]
    public string LastName { get; set; }
    // more properties here in the real example, some of which nest to properties that use their own JsonConverters.
}

这个玩具示例的 JsonConverter(内容并不真正相关；相关的是我将它用于属性):

public class AllCapsConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
        => objectType == typeof(string);

    public override bool CanRead => false;

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotSupportedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var str = value as string;
        var upper = str.ToUpperInvariant();
        JToken j = JToken.FromObject(upper);
        j.WriteTo(writer);
    }
}

通过单元测试:

public class PersonSerializationTest
{
    [Fact]
    public void SerializePerson_LastNameCaps()
    {
        var person = new Person
        {
            FirstName = "George",
            LastName = "Washington"
        };
        var serialized = JsonConvert.SerializeObject(person);
        var expected = @"{""FirstName"":""George"",""LastName"":""WASHINGTON""}";
        Assert.Equal(expected, serialized);
    }
}

Answer 1

您可以通过自定义 ContractResolver 以编程方式将 JsonConverter 应用于模型类中的一个或多个属性，而无需使用属性。这是一个非常简单的示例，它将您的 AllCapsConverter 应用于 Person 类中的 LastName 属性。 (如果您正在寻找更强大的解决方案，请查看@dbc 的 answer 。我在这里的目的是展示可能可行的最简单示例。)

public class CustomResolver : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty prop = base.CreateProperty(member, memberSerialization);
        if (prop.DeclaringType == typeof(Person) && prop.UnderlyingName == "LastName")
        {
            prop.Converter = new AllCapsConverter();
        }
        return prop;
    }
}

这里是更新的测试和 Person 模型，展示了如何使用解析器:

public class PersonSerializationTest
{
    [Fact]
    public void SerializePerson_LastNameCaps()
    {
        var person = new Person
        {
            FirstName = "George",
            LastName = "Washington"
        };
        var settings = new JsonSerializerSettings
        {
            ContractResolver = new CustomResolver()
        };
        var serialized = JsonConvert.SerializeObject(person, settings);
        var expected = @"{""FirstName"":""George"",""LastName"":""WASHINGTON""}";
        Assert.Equal(expected, serialized);
    }
}

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

工作演示:https://dotnetfiddle.net/o4e3WP