C# JsonConvert SerializeXmlNode 空属性

Question

我正在使用 JsonConvert SerializeXmlNode 将 xml 转换为 json。我面临的问题是我有一个标签，它有时可以有值(value)，有时可以为空

<AustrittDatum>2018-01-31+01:00</AustrittDatum>
...
<AustrittDatum xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>

结果 - 当我尝试将 json 反序列化为具有字符串属性“AustrittDatum”的 C# 对象时出现异常 - “Newtonsoft.Json.JsonReaderException:‘读取字符串时出错。意外的标记:StartObject。路径‘AustrittDatum’。”", 因为

<AustrittDatum xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance xsi:nil="true"/> 

被序列化为

"AustrittDatum": {
  "@xmlns:xsi": "http://www.w3.org/2001/XMLSchema-instance",
  "@xsi:nil": "true"
},

我怎样才能强制它像这样 "AustrittDatum": "" 或者也许有一些正确的方法来解决它？

Answer 1

似乎，当遇到带有 xsi:nil="true" 的 XML 元素时, Json.NET 的 XmlNodeConverter使用您看到的属性创建一个 JSON 对象，而不是 null JToken .这与 Newtonsoft 文档页面 Converting between JSON and XML 一致:

Converstion Rules

• Elements remain unchanged.
• Attributes are prefixed with an @ and should be at the start of the object.
• Single child text nodes are a value directly against an element, otherwise they are accessed via #text.
• The XML declaration and processing instructions are prefixed with ?.
• Character data, comments, whitespace and significant whitespace nodes are accessed via #cdata-section, #comment, #whitespace and #significant-whitespace respectively.
• Multiple nodes with the same name at the same level are grouped together into an array.
• Empty elements are null.

If the XML created from JSON doesn't match what you want, then you will need to convert it manually...

尽管如此，认为具有 xsi:nil="true" 的元素将被转换为 null JSON 值是合理的，因为 xsi:nil 是 predefined w3c attribute .可能 Newtonsoft 没有这样做，因为这样的元素可以携带额外的属性，如果元素被转换为 null，这些属性将会丢失。

您可以提交 enhancement request对于 XmlNodeConverter 如果您愿意，但与此同时，以下扩展方法将对 JToken 层次结构进行后处理并转换以前为 nil 元素的对象为空 JSON 值:

public static class JTokenExtensions
{
    const string XsiNamespace = @"http://www.w3.org/2001/XMLSchema-instance";
    readonly static string XmlNullValue = System.Xml.XmlConvert.ToString(true);

    public static JToken ReplaceXmlNilObjectsWithNull(this JToken root)
    {
        return root.ReplaceXmlNilObjects(t => JValue.CreateNull());
    }

    public static JToken ReplaceXmlNilObjects(this JToken root, Func<JToken, JToken> getReplacement)
    {
        var query = from obj in root.DescendantsAndSelf().OfType<JObject>()
                    where obj.Properties().Any(p => p.IsNilXmlTrueProperty())
                    select obj;
        foreach (var obj in query.ToList())
        {
            var replacement = getReplacement(obj);
            if (obj == root)
                root = replacement;
            if (obj.Parent != null)
                obj.Replace(replacement);
        }
        return root;
    }

    static IEnumerable<JToken> DescendantsAndSelf(this JToken node)
    {
        // Small wrapper adding this method to all JToken types.
        if (node == null)
            return Enumerable.Empty<JToken>();
        var container = node as JContainer;
        if (container != null)
            return container.DescendantsAndSelf();
        else
            return new[] { node };
    }

    static string GetXmlNamespace(this JProperty prop)
    {
        if (!prop.Name.StartsWith("@"))
            return null;
        var index = prop.Name.IndexOf(":");
        if (index < 0 || prop.Name.IndexOf(":", index+1) >= 0)
            return null;
        var ns = prop.Name.Substring(1, index - 1);
        if (string.IsNullOrEmpty(ns))
            return null;
        var nsPropertyName = "@xmlns:" + ns;
        foreach (var obj in prop.AncestorsAndSelf().OfType<JObject>())
        {
            var nsProperty = obj[nsPropertyName];
            if (nsProperty != null && nsProperty.Type == JTokenType.String)
                return (string)nsProperty;
        }
        return null;
    }

    static bool IsNilXmlTrueProperty(this JProperty prop)
    {
        if (prop == null)
            return false;
        if (!(prop.Value.Type == JTokenType.String && (string)prop.Value == "true"))
            return false;
        if (!(prop.Name.StartsWith("@") && prop.Name.EndsWith(":nil")))
            return false;
        var ns = prop.GetXmlNamespace();
        return ns == XsiNamespace;
    }
}

然后像这样使用它:

// Parse XML to XDocument
var xDoc = XDocument.Parse(xmlString);

// Convert the XDocument to an intermediate JToken hierarchy.
var converter = new Newtonsoft.Json.Converters.XmlNodeConverter { OmitRootObject = true };
var rootToken = JObject.FromObject(xDoc, JsonSerializer.CreateDefault(new JsonSerializerSettings { Converters = { converter } } ))
    // And replace xsi:nil objects will null JSON values
    .ReplaceXmlNilObjectsWithNull();

// Deserialize to the final RootObject.
var rootObject = rootToken.ToObject<RootObject>();

生成:

"AustrittDatum": [
  "2018-01-31+01:00",
  null
],

这里我最初解析为 XDocument但你也可以使用旧的 XmlDocument

sample 加工 .Net fiddle .