如何即时将属性添加到JSON对象

Question

我们在项目中使用Json.Net来序列化和序列化JSON对象。

我们的实体具有一些DateTime属性，我希望能够将它们转换为PersianCalender DateTime并在我的JSON对象中作为字符串提供：

例如，我们有这个实体：

public class PersonCertificate
{
      public DateTime CertificateDate{get;set;}
}

我想拥有这样的json对象：

{
    "PersianCertificateDate":"1395/10/10"
}

所以我认为将一个名为" aspersiandate"的属性很棒，这样我就可以做这样的事情：

public class PersonCertificate
{
      [JsonIgnore]
      [AsPersianDate]
      public DateTime CertificateDate{get;set;}
}

我知道我可以有一个自定义合同解析器来拦截JSON属性创建过程，但我不知道该如何告诉Json.Net将PersianCertificateDate置于CertificateDate中？

Answer 1

好吧，它比我想象的要容易得多。实际上，违规者负责获取和设置所有属性值，所以这就是我所做的：

public class EntityContractResolver:DefaultContractResolver
    {
        private class PersianDateValueProvider:IValueProvider
        {
            private readonly PropertyInfo _propertyInfo;
            public PersianDateValueProvider(PropertyInfo propertyInfo)
            {
                _propertyInfo = propertyInfo;
            }

            public void SetValue(object target, object value)
            {
                try
                {
                    var date = value as string;
                    if(value==null && _propertyInfo.PropertyType==typeof(DateTime))
                        throw new InvalidDataException();
                    _propertyInfo.SetValue(target,date.ToGregorianDate());
                }
                catch (InvalidDataException)
                {
                    throw new ValidationException(new[]
                    {
                        new ValidationError
                        {
                            ErrorMessage = "Date is not valid",
                            FieldName = _propertyInfo.Name,
                            TypeName = _propertyInfo.DeclaringType.FullName
                        }
                    });
                }
            }
            public object GetValue(object target)
            {
                if(_propertyInfo.PropertyType.IsNullable() && _propertyInfo.GetValue(target)==null) return null;
                try
                {
                    return ((DateTime) _propertyInfo.GetValue(target)).ToPersian();
                }
                catch
                {
                    return string.Empty;
                }
            }
        }

        protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
        {
            var list= base.CreateProperties(type, memberSerialization).ToList();
            list.AddRange(type.GetProperties()
                .Where(pInfo => IsAttributeDefined(pInfo,typeof(AsPersianDateAttribute))&& (pInfo.PropertyType == typeof (DateTime) || pInfo.PropertyType == typeof (DateTime?)))
                .Select(CreatePersianDateTimeProperty));
            return list;
        }
        private JsonProperty CreatePersianDateTimeProperty(PropertyInfo propertyInfo)
        {
            return new JsonProperty
            {
                PropertyName = "Persian"+propertyInfo.Name ,
                PropertyType = typeof (string),
                ValueProvider = new PersianDateValueProvider(propertyInfo),
                Readable = true,
                Writable = true
            };
        }
        private bool IsAttributeDefined(PropertyInfo propertyInfo,Type attribute)
        {
            var metaDataAttribute = propertyInfo.DeclaringType.GetCustomAttribute<MetadataTypeAttribute>(true);
            var metaDataProperty = metaDataAttribute?.MetadataClassType?.GetProperty(propertyInfo.Name);
            var metaDataHasAttribute = metaDataProperty != null && Attribute.IsDefined(metaDataProperty, attribute);
            return metaDataHasAttribute || Attribute.IsDefined(propertyInfo, attribute);
        }
    }