使用 JSON.NET 序列化时如何将属性从接口继承到对象

Question

using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using System.Text;
using System.IO;
using System.Runtime.Serialization;
using Newtonsoft.Json.Serialization;
using System.Linq;
using System.Reflection;
public interface IParent
{
    [JsonProperty]
    int Id {get;set;}
}

[JsonObject(MemberSerialization.OptIn)]
public class Parent : IParent
{
    public int Id { get;set; }  
    public string Name {get;set;}   
}

public class Serializer
{
    public static void Main()
    {

        var parent = new Parent() { Id = 1, Name ="Parent"};        
        var sb = new StringBuilder();
                var sw = new StringWriter(sb);

                var settings = new JsonSerializerSettings()
                       {
                           NullValueHandling = NullValueHandling.Ignore                            
                       };

            var output = JsonConvert.SerializeObject(parent, Formatting.None, settings);
                Console.WriteLine(output);
            Console.ReadKey();
    }
}

在上面的代码中，输出是{}。是否可以序列化并获得输出为{"Id":1}？

Answer 1

这是一个坏主意。

话虽如此，Newtonsoft 为您提供了一种更改序列化内容的方法：在这种情况下，您将子类化DefaultContractResolver并覆盖CreateProperty.

问题是，根据接口的属性决定何时应该选择序列化并不容易。一方面，一个类可能会实现多个具有冲突序列化指令的接口。此外，将对象反序列化为声明为冲突接口（例如）的变量是行不通的。它很脆弱，也不安全（它允许外部代码指定实例显示的数据）。

如果您必须这样做，以下代码适用于您的情况：

public class InterfaceContractResolver : DefaultContractResolver, IContractResolver
{
    public InterfaceContractResolver() : this(false) { }
    public InterfaceContractResolver(bool shareCache) : base (shareCache) {}

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var property = base.CreateProperty(member, memberSerialization);
        var interfaces = member.DeclaringType.GetInterfaces();
        foreach (var @interface in interfaces)
        {
            foreach (var interfaceProperty in @interface.GetProperties())
            {
                // This is weak: among other things, an implementation 
                // may be deliberately hiding an interface member
                if (interfaceProperty.Name == member.Name && interfaceProperty.MemberType == member.MemberType)
                {
                    if (interfaceProperty.GetCustomAttributes(typeof(JsonPropertyAttribute), true).Any())
                    {
                        property.Ignored = false;
                        return property;
                    }
                }
            }
        }
        return property;
    }

}

然后，当您创建序列化程序时，在设置中将解析程序的实例传递给它：

var settings = new JsonSerializerSettings()
{
    NullValueHandling = NullValueHandling.Ignore,
    ContractResolver = new InterfaceContractResolver(true)
};