How can I serialize an object with a Dictionary<string,object> property?

Question

In the example code below, I get this error:

Element TestSerializeDictionary123.Customer.CustomProperties vom Typ System.Collections.Generic.Dictionary`2[[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Object, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]] can not be serialized because it implements IDictionary.

When I take out the Dictionary property, it works fine.

How can I serialize this Customer object with the dictionary property? Or what replacement type for Dictionary can I use that would be serializable?

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

namespace TestSerializeDictionary123
{
    public class Program
    {
        static void Main(string[] args)
        {
            List<Customer> customers = Customer.GetCustomers();

            Console.WriteLine("--- Serializing ------------------");

            foreach (var customer in customers)
            {
                Console.WriteLine("Serializing " + customer.GetFullName() + "...");
                string xml = XmlHelpers.SerializeObject<Customer>(customer);
                Console.WriteLine(xml);
                Console.WriteLine("Deserializing ...");
                Customer customer2 = XmlHelpers.DeserializeObject<Customer>(xml);
                Console.WriteLine(customer2.GetFullName());
                Console.WriteLine("---");
            }

            Console.ReadLine();
        }
    }

    public static class StringHelpers
    {
        public static String UTF8ByteArrayToString(Byte[] characters)
        {
            UTF8Encoding encoding = new UTF8Encoding();
            String constructedString = encoding.GetString(characters);
            return (constructedString);
        }

        public static Byte[] StringToUTF8ByteArray(String pXmlString)
        {
            UTF8Encoding encoding = new UTF8Encoding();
            Byte[] byteArray = encoding.GetBytes(pXmlString);
            return byteArray;
        }
    }

    public static class XmlHelpers
    {
        public static string SerializeObject<T>(object o)
        {
            MemoryStream ms = new MemoryStream();
            XmlSerializer xs = new XmlSerializer(typeof(T));
            XmlTextWriter xtw = new XmlTextWriter(ms, Encoding.UTF8);
            xs.Serialize(xtw, o);
            ms = (MemoryStream)xtw.BaseStream;
            return StringHelpers.UTF8ByteArrayToString(ms.ToArray());
        }

        public static T DeserializeObject<T>(string xml)
        {
            XmlSerializer xs = new XmlSerializer(typeof(T));
            MemoryStream ms = new MemoryStream(StringHelpers.StringToUTF8ByteArray(xml));
            XmlTextWriter xtw = new XmlTextWriter(ms, Encoding.UTF8);
            return (T)xs.Deserialize(ms);
        }
    }

    public class Customer
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Street { get; set; }
        public string Location { get; set; }
        public string ZipCode { get; set; }
        public Dictionary<string,object> CustomProperties { get; set; }

        private int internalValue = 23;

        public static List<Customer> GetCustomers()
        {
            List<Customer> customers = new List<Customer>();
            customers.Add(new Customer { Id = 1, FirstName = "Jim", LastName = "Jones", ZipCode = "23434" });
            customers.Add(new Customer { Id = 2, FirstName = "Joe", LastName = "Adams", ZipCode = "12312" });
            customers.Add(new Customer { Id = 3, FirstName = "Jack", LastName = "Johnson", ZipCode = "23111" });
            customers.Add(new Customer { Id = 4, FirstName = "Angie", LastName = "Reckar", ZipCode = "54343" });
            customers.Add(new Customer { Id = 5, FirstName = "Henry", LastName = "Anderson", ZipCode = "16623" });
            return customers;
        }

        public string GetFullName()
        {
            return FirstName + " " + LastName + "(" + internalValue + ")";
        }

    }
}

Answer 1

I've just found this blog post by Rakesh Rajan which describes one possible solution:

Override XmlSerialization by making the type implement the System.Xml.Serialization.IXmlSerializable class. Define how you want the object to be serialized in XML in the WriteXml method, and define how you could recreate the object from an xml string in the ReadXml method.

But this wouldn't work as your Dictionary contains an object rather than a specific type.

Answer 2

You can't (short of doing it all yourself, which is horrible); the xml serializer isn't going to have a clue what to do with object, as it doesn't include type metadata in the wire format. One (hacky) option would be to stream these all as strings for the purposes of serialization, but then you have a lot of extra parsing (etc) code to write.

Answer 3

What about to mark Customer class as DataContract and its properties as DataMembers. DataContract serializer will do the serialization for you.

Answer 4

In our application we ended up using:

DataContractSerializer xs = new DataContractSerializer(typeof (T));

instead of:

XmlSerializer xs = new XmlSerializer(typeof (T));

which solved the problem as DatacontractSerializer supports Dictionary.

Another solution is ths XML Serializable Generic Dictionary workaround also works in the above example, and there is a long discussion at that link from people using it, might be useful for people working with this issue.

Answer 5

You can use Binary serialization instead. (Just make sure all your classes are marked as [Serializable]. Of course, it won't be in XML format, but you didn't list that as a requirement :)

Answer 6

Here's a generic dictionary class that knows how to serialize itself:

  public class XmlDictionary<T, V> : Dictionary<T, V>, IXmlSerializable {
    [XmlType("Entry")]
    public struct Entry {
      public Entry(T key, V value) : this() { Key = key; Value = value; }
      [XmlElement("Key")]
      public T Key { get; set; }
      [XmlElement("Value")]
      public V Value { get; set; }
    }
    System.Xml.Schema.XmlSchema IXmlSerializable.GetSchema() {
      return null;
    }
    void IXmlSerializable.ReadXml(System.Xml.XmlReader reader) {
      this.Clear();
      var serializer = new XmlSerializer(typeof(List<Entry>));
      reader.Read();  // Why is this necessary?
      var list = (List<Entry>)serializer.Deserialize(reader);
      foreach (var entry in list) this.Add(entry.Key, entry.Value);
      reader.ReadEndElement();
    }
    void IXmlSerializable.WriteXml(System.Xml.XmlWriter writer) {
      var list = new List<Entry>(this.Count);
      foreach (var entry in this) list.Add(new Entry(entry.Key, entry.Value));
      XmlSerializer serializer = new XmlSerializer(list.GetType());
      serializer.Serialize(writer, list);
    }
  }