c# - json 从遗留属性名称反序列化

Question

如何设置 Newtonsoft.Json 以使用旧成员名称反序列化对象，但使用当前成员名称对其进行序列化？

编辑:要求从正在序列化/反序列化的类中删除过时的成员。

这是一个需要序列化和反序列化的示例对象。我已经为一个属性提供了一个属性，其中包含一个名称列表，它可能在过去被序列化。

[DataContract]
class TestObject {
    [LegacyDataMemberNames("alpha", "omega")]
    [DataMember(Name = "a")]
    public int A { get; set; }
}

我想始终使用名称“a”进行 json 序列化，但能够从任何旧名称(包括“alpha”和“omega”以及当前名称“a”)反序列化为一个属性

Answer 1

这可以通过自定义 IContractResolver 来完成通过扩展 DefaultContractResolver 创建:

[System.AttributeUsage(System.AttributeTargets.Property | System.AttributeTargets.Field, AllowMultiple = false, Inherited = true)]
public class LegacyDataMemberNamesAttribute : Attribute
{
    public LegacyDataMemberNamesAttribute() : this(new string[0]) { }

    public LegacyDataMemberNamesAttribute(params string[] names) { this.Names = names; }

    public string [] Names { get; set; }
}

public class LegacyPropertyResolver : DefaultContractResolver
{
    protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
    {
        var properties = base.CreateProperties(type, memberSerialization);

        for (int i = 0, n = properties.Count; i < n; i++)
        {
            var property = properties[i];
            if (!property.Writable)
                continue;
            var attrs = property.AttributeProvider.GetAttributes(typeof(LegacyDataMemberNamesAttribute), true);
            if (attrs == null || attrs.Count == 0)
                continue;
            // Little kludgy here: use MemberwiseClone to clone the JsonProperty.
            var clone = property.GetType().GetMethod("MemberwiseClone", BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
            foreach (var name in attrs.Cast<LegacyDataMemberNamesAttribute>().SelectMany(a => a.Names))
            {
                if (properties.Any(p => p.PropertyName == name))
                {
                    Debug.WriteLine("Duplicate LegacyDataMemberNamesAttribute: " + name);
                    continue;
                }
                var newProperty = (JsonProperty)clone.Invoke(property, new object[0]);
                newProperty.Readable = false;
                newProperty.PropertyName = name;
                properties.Add(newProperty);
            }
        }

        return properties;
    }
}

然后将属性添加到您的类型中，如问题所示:

[DataContract]
class TestObject
{
    [LegacyDataMemberNames("alpha", "omega")]
    [DataMember(Name = "a")]
    public int A { get; set; }
}

构造和配置 LegacyPropertyResolver 实例，例如如下:

static IContractResolver legacyResolver = new LegacyPropertyResolver 
{ 
    // Configure as required, e.g. 
    // NamingStrategy = new CamelCaseNamingStrategy() 
};

然后在settings中使用它:

var settings = new JsonSerializerSettings { ContractResolver = legacyResolver };
var deserialized = JsonConvert.DeserializeObject<TestObject>(jsonString, settings);

注意事项:

• 此实现不要求类具有显式数据协定属性注释。如果愿意，您可以添加该限制。

• 你应该cache and reuse instances of contract resolvers以获得最佳性能。

演示 fiddle here .