如何使用 XmlSerializer 反序列化大型文档中的节点

How to deserialize a node in a large document using XmlSerializer(如何使用 XmlSerializer 反序列化大型文档中的节点)

问题描述

我有一个大型 XML 文档，已加载到 XmlDocument 中，我想使用 XmlSerializer 类将其中的选定元素反序列化为生成的 .NET 类使用 xsd.exe.

I have a large XML document that I have loaded into an XmlDocument and I want to use the XmlSerializer class to deserialize selected elements from it into a .NET class generated using xsd.exe.

这是迄今为止我尝试过的 MCVE；xsd 和生成的类在帖子的末尾.如代码中的注释中所述，我得到一个 InvalidOperationException - <Cars xmlns:'http://MyNamespace'/>没想到:

Here's an MCVE of what I've tried so far; the xsd and generated class are at the end of the post. As noted in the comments in the code, I am getting an InvalidOperationException - <Cars xmlns:'http://MyNamespace' /> was not expected:

static string XmlContent = @"
    <RootNode xmlns=""http://MyNamespace"">
        <Cars>
        <Car make=""Volkswagen"" />
        <Car make=""Ford"" />
        <Car make=""Opel"" />
        </Cars>
    </RootNode>";

static void TestMcve()
{
    var doc = new XmlDocument();
    doc.LoadXml(XmlContent);
    var nsMgr = new XmlNamespaceManager(doc.NameTable);
    nsMgr.AddNamespace("myns", "http://MyNamespace");
    var rootSerializer = new XmlSerializer(typeof(RootNode));
    var root = (RootNode) rootSerializer.Deserialize(new XmlNodeReader(doc));
    Console.WriteLine(root.Cars[0].make); // Works fine so far

    var node = doc.DocumentElement.SelectSingleNode("myns:Cars", nsMgr);
    Console.WriteLine(node.OuterXml);
    var carSerializer = new XmlSerializer(typeof(Car));
    using (var reader = new XmlNodeReader(node))
    {
        // What I want is a list of Car instances deserialized from
        // the Car child elements of the Cars element.
        // The following line throws an InvalidOperationException
        // "<Cars xmlns:'http://MyNamespace' /> was not expected"
        // If I change SelectSingleNode above to select "myns:Cars/myns:Car"
        // I get "<Car xmlns:'http://MyNamespace' /> was not expected"
        var result = carSerializer.Deserialize(reader);
    }
}

我还想随后更新我的 Car 类实例，并使用 XmlSerializer 将其插入回文档中，这是后续问题的主题 如何使用 XmlSerializer 在大文档中插入节点.

I also want to subsequently update my Car class instance, and insert it back into the document using the XmlSerializer, which is the subject of a follow-up question How to insert a node in a large document using XmlSerializer .

xsd 和生成的类如下:

The xsd and generated classes follow:

<xs:schema xmlns="http://MyNamespace" xmlns:xs="http://www.w3.org/2001/XMLSchema" 
           targetNamespace="http://MyNamespace" 
           elementFormDefault="qualified" attributeFormDefault="unqualified" 
           version="3.9.0.8">
  <xs:complexType name="Cars">
    <xs:sequence>
      <xs:element name="Car" type="Car" maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="Car">
    <xs:attribute name="make" type="xs:string" use="required"/>
  </xs:complexType>
  <xs:complexType name="RootNode">
    <xs:sequence>
      <xs:element name="Cars" type="Cars" minOccurs="0"/>
    </xs:sequence>
  </xs:complexType>
  <xs:element name="RootNode" type="RootNode" />
</xs:schema>

xsd.exe 生成的代码:

Code generated by xsd.exe:

using System.Xml.Serialization;


/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "4.6.1055.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(Namespace="http://MyNamespace")]
[System.Xml.Serialization.XmlRootAttribute(Namespace="http://MyNamespace", IsNullable=false)]
public partial class RootNode {

    private Car[] carsField;

    /// <remarks/>
    [System.Xml.Serialization.XmlArrayItemAttribute(IsNullable=false)]
    public Car[] Cars {
        get {
            return this.carsField;
        }
        set {
            this.carsField = value;
        }
    }
}

/// <remarks/>
[System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "4.6.1055.0")]
[System.SerializableAttribute()]
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.ComponentModel.DesignerCategoryAttribute("code")]
[System.Xml.Serialization.XmlTypeAttribute(Namespace="http://MyNamespace")]
public partial class Car {

    private string makeField;

    /// <remarks/>
    [System.Xml.Serialization.XmlAttributeAttribute()]
    public string make {
        get {
            return this.makeField;
        }
        set {
            this.makeField = value;
        }
    }
}

推荐答案

这里有两个问题:

1. var node = doc.DocumentElement.SelectSingleNode("myns:Cars", nsMgr); 位于 元素——<Car> 节点的重复序列的容器元素 - 但您的 XmlSerializer 被构造为反序列化名为 <Car>.尝试使用反序列化单个汽车的序列化程序反序列化一系列汽车是行不通的.

[System.Xml.Serialization.XmlTypeAttribute(Namespace = "http://MyNamespace")]
// Not included!
//[System.Xml.Serialization.XmlRootAttribute(Namespace = "http://MyNamespace")]
public partial class Car
{
}

public static partial class XmlNodeExtensions
{
    public static List<T> DeserializeList<T>(this XmlNodeList nodes)
    {
        return nodes.Cast<XmlNode>().Select(n => n.Deserialize<T>()).ToList();
    }

    public static T Deserialize<T>(this XmlNode node)
    {
        if (node == null)
            return default(T);
        var serializer = XmlSerializerFactory.Create(typeof(T), node.LocalName, node.NamespaceURI);
        using (var reader = new XmlNodeReader(node))
        {
            return (T)serializer.Deserialize(reader);
        }
    }
}

public static class XmlSerializerFactory
{
    // To avoid a memory leak the serializer must be cached.
    // https://stackoverflow.com/questions/23897145/memory-leak-using-streamreader-and-xmlserializer
    // This factory taken from 
    // https://stackoverflow.com/questions/34128757/wrap-properties-with-cdata-section-xml-serialization-c-sharp/34138648#34138648

    readonly static Dictionary<Tuple<Type, string, string>, XmlSerializer> cache;
    readonly static object padlock;

    static XmlSerializerFactory()
    {
        padlock = new object();
        cache = new Dictionary<Tuple<Type, string, string>, XmlSerializer>();
    }

    public static XmlSerializer Create(Type serializedType, string rootName, string rootNamespace)
    {
        if (serializedType == null)
            throw new ArgumentNullException();
        if (rootName == null && rootNamespace == null)
            return new XmlSerializer(serializedType);
        lock (padlock)
        {
            XmlSerializer serializer;
            var key = Tuple.Create(serializedType, rootName, rootNamespace);
            if (!cache.TryGetValue(key, out serializer))
                cache[key] = serializer = new XmlSerializer(serializedType, new XmlRootAttribute { ElementName = rootName, Namespace = rootNamespace });
            return serializer;
        }
    }
}

var nodes = doc.DocumentElement.SelectNodes("myns:Cars/myns:Car", nsMgr);
var cars = nodes.DeserializeList<Car>();