How to deserialize only part of an XML document in C#

Question

Here's a fictitious example of the problem I'm trying to solve. If I'm working in C#, and have XML like this:

<?xml version="1.0" encoding="utf-8"?> <Cars>   <Car>     <StockNumber>1020</StockNumber>     <Make>Nissan</Make>     <Model>Sentra</Model>   </Car>   <Car>     <StockNumber>1010</StockNumber>     <Make>Toyota</Make>     <Model>Corolla</Model>   </Car>   <SalesPerson>     <Company>Acme Sales</Company>     <Position>        <Salary>           <Amount>1000</Amount>           <Unit>Dollars</Unit>     ... and on... and on....   </SalesPerson> </Cars> 

the XML inside SalesPerson can be very long, megabytes in size. I want to deserialize the tag, but not deserialize the SalesPerson XML element instead keeping it in raw form "for later on".

Essentially I would like to be able to use this as a Objects representation of the XML.

[System.Xml.Serialization.XmlRootAttribute("Cars", Namespace = "", IsNullable = false)] public class Cars {     [XmlArrayItem(typeof(Car))]     public Car[] Car { get; set; }      public Stream SalesPerson { get; set; } }  public class Car {     [System.Xml.Serialization.XmlElementAttribute("StockNumber")]     public string StockNumber{ get; set; }      [System.Xml.Serialization.XmlElementAttribute("Make")]     public string Make{ get; set; }      [System.Xml.Serialization.XmlElementAttribute("Model")]     public string Model{ get; set; } } 

where the SalesPerson property on the Cars object would contain a stream with the raw xml that is within the <SalesPerson> xml element after being run through an XmlSerializer.

Can this be done? Can I choose to only deserialize "part of" an xml document?

Thanks! -Mike

p.s. example xml stolen from How to Deserialize XML document

Answer 1

It might be a bit old thread, but i will post anyway. i had the same problem (needed to deserialize like 10kb of data from a file that had more than 1MB). In main object (which has a InnerObject that needs to be deserializer) i implemented a IXmlSerializable interface, then changed the ReadXml method.

We have xmlTextReader as input , the first line is to read till a XML tag:

reader.ReadToDescendant("InnerObjectTag"); //tag which matches the InnerObject 

Then create XMLSerializer for a type of the object we want to deserialize and deserialize it

XmlSerializer   serializer = new XmlSerializer(typeof(InnerObject));  this.innerObject = serializer.Deserialize(reader.ReadSubtree()); //this gives serializer the part of XML that is for  the innerObject data  reader.close(); //now skip the rest  

this saved me a lot of time to deserialize and allows me to read just a part of XML (just some details that describe the file, which might help the user to decide if the file is what he wants to load).

Answer 2

The accepted answer from user271807 is a great solution but I found, that I also needed to set the xml root of the fragment to avoid an exception with an inner exception saying something like this:

...xmlns=''> was not expected 

This exception was trown when I tried to deserialize only the inner Authentication element of this xml document:

<?xml version=""1.0"" encoding=""UTF-8""?> <Api>   <Authentication>                              <sessionid>xxx</sessionid>       <errormessage>xxx</errormessage>                   </Authentication> </ApI> 

So I ended up creating this extension method as a reusable solution - warning contains a memory leak, see below:

public static T DeserializeXml<T>(this string @this, string innerStartTag = null)         {             using (var stringReader = new StringReader(@this))             using (var xmlReader = XmlReader.Create(stringReader)) {                 if (innerStartTag != null) {                     xmlReader.ReadToDescendant(innerStartTag);                     var xmlSerializer = new XmlSerializer(typeof(T), new XmlRootAttribute(innerStartTag));                     return (T)xmlSerializer.Deserialize(xmlReader.ReadSubtree());                 }                 return (T)new XmlSerializer(typeof(T)).Deserialize(xmlReader);             }         } 

Update 20th March 2017:As the comment below points out, there is a memory leak problem when using one of the constructors of XmlSerializer, so I ended up using a caching solution as shown below:

    /// <summary>     ///     Deserialize XML string, optionally only an inner fragment of the XML, as specified by the innerStartTag parameter.     /// </summary>     public static T DeserializeXml<T>(this string @this, string innerStartTag = null) {         using (var stringReader = new StringReader(@this)) {             using (var xmlReader = XmlReader.Create(stringReader)) {                 if (innerStartTag != null) {                     xmlReader.ReadToDescendant(innerStartTag);                     var xmlSerializer = CachingXmlSerializerFactory.Create(typeof (T), new XmlRootAttribute(innerStartTag));                     return (T) xmlSerializer.Deserialize(xmlReader.ReadSubtree());                 }                 return (T) CachingXmlSerializerFactory.Create(typeof (T), new XmlRootAttribute("AutochartistAPI")).Deserialize(xmlReader);             }         }     } /// <summary> ///     A caching factory to avoid memory leaks in the XmlSerializer class. /// See http://dotnetcodebox.blogspot.dk/2013/01/xmlserializer-class-may-result-in.html /// </summary> public static class CachingXmlSerializerFactory {     private static readonly ConcurrentDictionary<string, XmlSerializer> Cache = new ConcurrentDictionary<string, XmlSerializer>();     public static XmlSerializer Create(Type type, XmlRootAttribute root) {         if (type == null) {             throw new ArgumentNullException(nameof(type));         }         if (root == null) {             throw new ArgumentNullException(nameof(root));         }         var key = string.Format(CultureInfo.InvariantCulture, "{0}:{1}", type, root.ElementName);         return Cache.GetOrAdd(key, _ => new XmlSerializer(type, root));     }     public static XmlSerializer Create<T>(XmlRootAttribute root) {         return Create(typeof (T), root);     }     public static XmlSerializer Create<T>() {         return Create(typeof (T));     }     public static XmlSerializer Create<T>(string defaultNamespace) {         return Create(typeof (T), defaultNamespace);     }     public static XmlSerializer Create(Type type) {         return new XmlSerializer(type);     }     public static XmlSerializer Create(Type type, string defaultNamespace) {         return new XmlSerializer(type, defaultNamespace);     } }