如何从 JsonConvert.PopulateObject 中排除某些基类型或接口中不存在的属性？

Question

是否可以为 JsonConvert.PopulateObject 定义选项以排除 json 中给定的字段，这些字段在目标对象的接口实现中不存在？

public interface IElementWriter
{
    string Name { get; set; }
}
public interface IElementUpdateWriter : IElementWriter
{
    string FirstName { get; set; }
}
public interface IElementInsertWriter : IElementWriter
{
    DateTime? CreationDate { get; set; }
}

public class Element:IElementWriter, IElementInsertWriter, IElementUpdateWriter {
    public int ID { get; set; }
    public string Name { get; set; }
    public DateTime? CreationDate { get; set; }
    public string FirstName { get; set; }
}

static void Main(string[] args)
{
    IElementWriter element = new Element() { ID = 1, Name = "SourceName", CreationDate=DateTime.Today, FirstName="SourceFirstName" };

    string json = "{ id:'8', Name:'newName', FirstName:'newFirstName' }";

    JsonConvert.PopulateObject(json, element, new JsonSerializerSettings() {

    });
    Console.WriteLine(JsonConvert.SerializeObject(element));
    Console.ReadLine();
}

结果:

{"ID":8,"Name":"newName","CreationDate":"2019-06-05T00:00:00+02:00","FirstName":"newFirstName"}

必需因为 IElementWriter 没有 ID 也没有 FirstName:

{"ID":1,"Name":"newName","CreationDate":"2019-06-05T00:00:00+02:00","FirstName":"SourceFirstName"}

Answer 1

JsonSerializerSettings 中没有简单的设置会直接从其类型导致 JsonConvert.PopulateObject() to populate an instance of a derived type as if it were an instance of some base type. To confirm this, you can check the source for JsonSerializerInternalReader.Populate(), which takes as arguments only a reader and target and pulls the target's contract:

public void Populate(JsonReader reader, object target)
{
    Type objectType = target.GetType();

    JsonContract contract = Serializer._contractResolver.ResolveContract(objectType);

因此您的选择包括：

修改您的 Element class 的定义并将 [JsonIgnore] 添加到您不想填充的属性中。

您可能不想这样做，因为它会阻止属性被序列化或反序列化。
使用 custom contract resolver 忽略不属于 IElementWriter.
的所有 Element 属性
这似乎是更好的解决方案。

假设您选择选项 #2，您可以引入以下自定义合约解析器：

public class UpcastingContractResolver<TDerived, TBase> : DefaultContractResolver where TDerived: TBase
{
    readonly HashSet<string> baseProperties = ((JsonObjectContract)JsonSerializer.Create().ContractResolver.ResolveContract(typeof(TBase)))
        .Properties.Select(p => p.UnderlyingName)
        .ToHashSet();

    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
    {
        var properties = base.CreateProperties(type, memberSerialization);
        if (type == typeof(TDerived) || type.IsSubclassOf(typeof(TDerived)))
        {
            foreach (var property in properties)
            {
                if (!baseProperties.Contains(property.UnderlyingName))
                    property.Ignored = true;
            }
        }
        return properties;
    }
}

然后，在某处缓存一个实例以提高性能 suggested by Newtonsoft:

static IContractResolver elementAsElementWriterResolver = new UpcastingContractResolver<Element, IElementWriter>();

并按如下方式填充您的 element：

// Only populate those properties present in IElementWriter
JsonConvert.PopulateObject(json, element, new JsonSerializerSettings
                           { 
                               ContractResolver = elementAsElementWriterResolver 
                           });

演示 fiddle here.

如何从 JsonConvert.PopulateObject 中排除某些基类型或接口中不存在的属性？

How to exclude properties from JsonConvert.PopulateObject that don't exist in some base type or interface?

c#

serialization

interface

json.net

populate