C# – Deserializing XML into class obj in C#

cnetxmlxml-serialization

This is one of the entries I have in a huge XML file of over 200 such entries.

<TradeFills>
 <TradeFill>
  <Broker>xxx</Broker>
  <CustomerAccount/>
  <qwFillTransID>xxxxxxxxxxxxxxxxxxx</qwFillTransID>
  <qwPrevTransID>xxx</qwPrevTransID>
  <qwGroupTransID>xxxxxxxxxxxxxxxxx</qwGroupTransID>
  <GroupTransID>xxxxxxxx</GroupTransID>
  <TransID>x</TransID>
  <Service>xxxxxxxxxxxxxxxx</Service>
  <Symbol>xx</Symbol>
  <Exchange>xxxxx</Exchange>
  <InstClass>xxxxxxxx</InstClass>
  <InstSubClass>xxxxxxx</InstSubClass>
  <ContractSymbol>xxxx</ContractSymbol>
  <ExpirationDate>xxxxxxxx</ExpirationDate>
  <Month>xx</Month>
  <Year>xxxx</Year>
  <Strike>xxx</Strike>
  <TradePCU>xxxx</TradePCU>
  <Buy>x</Buy>
  <Quantity>xx</Quantity>
  <Price>xxxxx</Price>
  <FillTime>xxxxxxxxxxxxxxx</FillTime>
  <PosUpdated>xxxxxxxxxxx</PosUpdated>
  <Description/>
 </TradeFill>
</TradeFills>

I am attempting to deserialize this into a class object but failing every time.

This is my code so far:

using System;

using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Xml.Serialization;

namespace DeserializeXML
{
public class Program
{

    // This is the class that will be deserialized.
    [Serializable()]
    public class TradeFill
    {
        [XmlElement("Broker")]
        public string broker;

        [XmlElement("qwFillTransID")]
        public string qwFillTransId;

        [XmlElement("qwPrevTransID")]
        public string qwPrevTransId;

        [XmlElement("qwGroupTransID")]
        public string qwGroupTransId;

        [XmlElement("GroupTransID")]
        public string GroupTransID;

        [XmlElement("TransID")]
        public string TransId;

        [XmlElement("Service")]
        public string Service;

        [XmlElement("Exchange")]
        public string Exchange;

        [XmlElement("InstClass")]
        public string InstClass;

        [XmlElement("InstSubClass")]
        public string InstSubClass;

        [XmlElement("ContractSymbol")]
        public string ConSymbol;

        [XmlElement("ExpirationDate")]
        public DateTime ExpDate;

        [XmlElement("Month")]
        public int month;

        [XmlElement("Year")]
        public int year;

        [XmlElement("Strike")]
        public double strike;

        [XmlElement("TradePCU")]
        public string TradePCU;

        [XmlElement("Buy")]
        public int buy;

        [XmlElement("Quantity")]
        public int quantity;

        [XmlElement("Price")]
        public double price;

        [XmlElement("FillTime")]
        public DateTime FillTime;

        [XmlElement("PosUpdated")]
        public string PosUpdated;

    }


    [XmlRootAttribute("TradeFills")]
    public class SIGTrades
    {
        [XmlElement("TradeFills")]
        public TradeFill[] TradeFills{ get; set; }
    }


    [Serializable()]
    public class Test
    {
         public static void Main()
        {
            Test t = new Test();
          // Read a purchase order.
            t.DeserializeObject("c:\\test.xml");
        }

        private void DeserializeObject(string filename)
        {   
            Console.WriteLine("Reading with Stream");
            // Create an instance of the XmlSerializer.
            XmlSerializer serializer =
            new XmlSerializer(typeof(TradeFill));
            // Reading the XML document requires a FileStream.
            Stream reader= new FileStream(filename,FileMode.Open);

            // Declare an object variable of the type to be deserialized.
            TradeFill i;

            // Call the Deserialize method to restore the object's state.
            i = (TradeFill)serializer.Deserialize(reader);

            // Write out the properties of the object.
            Console.Write(i.qwFillTransId);
        }
    }


}

}

When I execute it, I only see "Reading with Stream" on the console, and nothing else.

EDIT

I just realized I say only 'Reading with stream" because it was still reading. After about 5 seconds, this is what I got:

Unhandled Exception: System.InvalidOperationException: DeserializeXML.Program is
 inaccessible due to its protection level. Only public types can be processed.
   at System.Xml.Serialization.TypeDesc.CheckSupported()
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo sourc
e, Boolean directReference, Boolean throwOnError)
   at System.Xml.Serialization.TypeScope.ImportTypeDesc(Type type, MemberInfo me
mberInfo, Boolean directReference)
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo sourc
e, Boolean directReference, Boolean throwOnError)
   at System.Xml.Serialization.ModelScope.GetTypeModel(Type type, Boolean direct
Reference)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type type
, XmlRootAttribute root, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultName
space)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type)
   at DeserializeXML.Program.Test.DeserializeObject(String filename) in c:\docum
ents and settings\sobti\my documents\visual studio 2010\Projects\DeserializeXML\
DeserializeXML\Program.cs:line 109
   at DeserializeXML.Program.Test.Main() in c:\documents and settings\sobti\my d
ocuments\visual studio 2010\Projects\DeserializeXML\DeserializeXML\Program.cs:li
ne 102

EDIT

After making my Program class public, I now get this error:

Unhandled Exception: System.InvalidOperationException: There was an error reflec
ting type 'DeserializeXML.Program.TradeFill'. ---> System.InvalidOperationExcept
ion: There was an error reflecting field 'GroupTransId'. ---> System.InvalidOper
ationException: The XML element 'qwGroupTransId' from namespace '' is already pr
esent in the current scope. Use XML attributes to specify another XML name or na
mespace for the element.
   at System.Xml.Serialization.XmlReflectionImporter.AddUniqueAccessor(INameScop
e scope, Accessor accessor)
   at System.Xml.Serialization.XmlReflectionImporter.AddUniqueAccessor(MemberMap
ping member, INameScope elements, INameScope attributes, Boolean isSequence)
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(Str
uctMapping mapping, StructModel model, Boolean openModel, String typeName, Recur
sionLimiter limiter)

EDIT

made a bunch of changes to my code (as reflected above). Had some items listed twice, double checked case etc. I now get this error:

Unhandled Exception: System.InvalidOperationException: There is an error in XML
document (2, 2). ---> System.InvalidOperationException: <TradeFills xmlns=''> wa
s not expected.
   at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderTradeF
ill.Read3_TradeFill()
   --- End of inner exception stack trace ---

Best Answer

Try changing this:

class Program
    {

to this

public class Program
    {

If you don't specify an access modifier then it uses the default of internal

Microsoft consistently violates those rules

Okay, #2 and #3 anyway. Our beloved dictionary has 2 internal structs:

[StructLayout(LayoutKind.Sequential)]  // default for structs
private struct Entry  //<Tkey, TValue>
{
    //  View code at *Reference Source
}

[Serializable, StructLayout(LayoutKind.Sequential)]
public struct Enumerator : 
    IEnumerator<KeyValuePair<TKey, TValue>>, IDisposable, 
    IDictionaryEnumerator, IEnumerator
{
    //  View code at *Reference Source
}

*Reference Source

The 'JonnyCantCode.com' source got 3 out of 4 - quite forgivable since #4 probably wouldn't be an issue. If you find yourself boxing a struct, rethink your architecture.

Let's look at why Microsoft would use these structs:

Each struct, Entry and Enumerator, represent single values.
Speed
Entry is never passed as a parameter outside of the Dictionary class. Further investigation shows that in order to satisfy implementation of IEnumerable, Dictionary uses the Enumerator struct which it copies every time an enumerator is requested ...makes sense.
Internal to the Dictionary class. Enumerator is public because Dictionary is enumerable and must have equal accessibility to the IEnumerator interface implementation - e.g. IEnumerator getter.

Update - In addition, realize that when a struct implements an interface - as Enumerator does - and is cast to that implemented type, the struct becomes a reference type and is moved to the heap. Internal to the Dictionary class, Enumerator is still a value type. However, as soon as a method calls GetEnumerator(), a reference-type IEnumerator is returned.

What we don't see here is any attempt or proof of requirement to keep structs immutable or maintaining an instance size of only 16 bytes or less:

Nothing in the structs above is declared readonly - not immutable
Size of these struct could be well over 16 bytes
Entry has an undetermined lifetime (from Add(), to Remove(), Clear(), or garbage collection);

And ... 4. Both structs store TKey and TValue, which we all know are quite capable of being reference types (added bonus info)

Hashed keys notwithstanding, dictionaries are fast in part because instancing a struct is quicker than a reference type. Here, I have a Dictionary<int, int> that stores 300,000 random integers with sequentially incremented keys.

Capacity: 312874
MemSize: 2660827 bytes
Completed Resize: 5ms
Total time to fill: 889ms

Capacity: number of elements available before the internal array must be resized.

MemSize: determined by serializing the dictionary into a MemoryStream and getting a byte length (accurate enough for our purposes).

Completed Resize: the time it takes to resize the internal array from 150862 elements to 312874 elements. When you figure that each element is sequentially copied via Array.CopyTo(), that ain't too shabby.

Total time to fill: admittedly skewed due to logging and an OnResize event I added to the source; however, still impressive to fill 300k integers while resizing 15 times during the operation. Just out of curiosity, what would the total time to fill be if I already knew the capacity? 13ms

So, now, what if Entry were a class? Would these times or metrics really differ that much?

Capacity: 312874
MemSize: 2660827 bytes
Completed Resize: 26ms
Total time to fill: 964ms

Obviously, the big difference is in resizing. Any difference if Dictionary is initialized with the Capacity? Not enough to be concerned with ... 12ms.

What happens is, because Entry is a struct, it does not require initialization like a reference type. This is both the beauty and the bane of the value type. In order to use Entry as a reference type, I had to insert the following code:

/*
 *  Added to satisfy initialization of entry elements --
 *  this is where the extra time is spent resizing the Entry array
 * **/
for (int i = 0 ; i < prime ; i++)
{
    destinationArray[i] = new Entry( );
}
/*  *********************************************** */

The reason I had to initialize each array element of Entry as a reference type can be found at MSDN: Structure Design. In short:

Do not provide a default constructor for a structure.

If a structure defines a default constructor, when arrays of the structure are created, the common language runtime automatically executes the default constructor on each array element.

Some compilers, such as the C# compiler, do not allow structures to have default constructors.

It is actually quite simple and we will borrow from Asimov's Three Laws of Robotics:

The struct must be safe to use
The struct must perform its function efficiently, unless this would violate rule #1
The struct must remain intact during its use unless its destruction is required to satisfy rule #1

...what do we take away from this: in short, be responsible with the use of value types. They are quick and efficient, but have the ability to cause many unexpected behaviors if not properly maintained (i.e. unintentional copies).

Best Answer

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Microsoft consistently violates those rules

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