将空XML元素反序列化为Guid.Empty

Question

我有一些反序列化的麻烦.

<Order>
    ...
    <CardNumber />
    ...
</Order>

如果我使用

<CardNumber>00000000-0000-0000-0000-000000000000</CardNumber>

它正常工作,但万一我只使用<CardNumber />- 对象不反序列化(

有没有办法将空元素反序列化为Guid.Empty？

应该使用此元素的值映射的属性:

[XmlElement(ElementName = "CardNumber")]
[JsonProperty("CardNumber")]
public Guid? CardNumber { get; set; }

JSON中的相同情况正常工作并使用Guid.Empty而不是空元素值

{
    "CardNumber": ""
}

Answer 1

您看到的异常清楚地说明了问题：

System.InvalidOperationException occurred
  Message="There is an error in XML document (3, 3)."
  InnerException: System.FormatException
       Message="Guid should contain 32 digits with 4 dashes (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)."

如前所述，XmlSerializer不支持将空字符串反序列化为Guid. 因此，您需要使用代理属性手动进行转换：

[XmlRoot("Order")]
public class Order
{
    [XmlIgnore]
    [JsonProperty("CardNumber")]
    public Guid? CardNumber { get; set; }

    [XmlElement(ElementName = "CardNumber", IsNullable = true)]
    [Browsable(false), EditorBrowsable(EditorBrowsableState.Never), DebuggerBrowsable(DebuggerBrowsableState.Never)]
    [JsonIgnore]
    public string XmlCardNumber
    {
        get
        {
            if (CardNumber == null)
                return null;
            else if (CardNumber.Value == Guid.Empty)
                return "";
            return XmlConvert.ToString(CardNumber.Value);
        }
        set
        {
            if (value == null)
                CardNumber = null;
            else if (string.IsNullOrEmpty(value))
                CardNumber = Guid.Empty;
            else
                CardNumber = XmlConvert.ToGuid(value);
        }
    }
}

如果您需要在许多具有属性的不同类型中执行此操作Guid?，则可以像这样提取代理类型：

[XmlType(AnonymousType = true, IncludeInSchema = false)]
public class XmlGuid
{
    [XmlIgnore]
    public Guid Guid { get; set; }

    [XmlText]
    public string XmlCardNumber
    {
        get
        {
            if (Guid == Guid.Empty)
                return null;
            return XmlConvert.ToString(Guid);
        }
        set
        {
            if (string.IsNullOrEmpty(value))
                Guid = Guid.Empty;
            else
                Guid = XmlConvert.ToGuid(value);
        }
    }

    public static implicit operator Guid?(XmlGuid x)
    {
        if (x == null)
            return null;
        return x.Guid;

    }

    public static implicit operator XmlGuid(Guid? g)
    {
        if (g == null)
            return null;
        return new XmlGuid { Guid = g.Value };
    }

    public static implicit operator Guid(XmlGuid x)
    {
        if (x == null)
            return Guid.Empty;
        return x.Guid;

    }

    public static implicit operator XmlGuid(Guid g)
    {
        return new XmlGuid { Guid = g };
    }
}

并像这样使用它：

[XmlRoot("Order")]
public class Order
{
    [XmlElement(Type = typeof(XmlGuid), ElementName = "CardNumber", IsNullable = true)]
    [JsonProperty("CardNumber")]
    public Guid? CardNumber { get; set; }
}

在这里，我利用了这样一个事实：该XmlElementAttribute.Type属性会自动获取我为from 和 to定义的隐式转换。Guid?XmlGuid