Why is there no XML serializable dictionary in .NET?

Question

I need a dictionary to serialize XML. In fact, I now have two completely different programs that need this. I was pretty surprised to see that .NET doesn't have one. I asked a question elsewhere and got sarcastic answers. I do not understand why this is a stupid question.

Can anyone enlighten me considering how the various dependent .NET functions are related to XML serialization, why there is no dictionary for XML serialization. Hope you can also explain why some people find this stupid question. I guess I should miss something fundamental, and I hope that you can fill in the blanks.

Answer 1

The thing about XML Serialization is that it is not just creating a stream of bytes. It is also about creating an XML schema with which this byte stream will be validated. There is no good way to represent a dictionary in an XML schema. The best you can do is show that there is a unique key.

You can always create your own shell, for example, One way to serialize dictionaries .

Answer 2

I know that this was answered before, but since I have a very concise way (code) to serialize IDictionary with the DataContractSerializer class (used by WCF, but it can and should be used anywhere), I could not resist it here :

public static class SerializationExtensions { public static string Serialize<T>(this T obj) { var serializer = new DataContractSerializer(obj.GetType()); using (var writer = new StringWriter()) using (var stm = new XmlTextWriter(writer)) { serializer.WriteObject(stm, obj); return writer.ToString(); } } public static T Deserialize<T>(this string serialized) { var serializer = new DataContractSerializer(typeof(T)); using (var reader = new StringReader(serialized)) using (var stm = new XmlTextReader(reader)) { return (T)serializer.ReadObject(stm); } } } 

This works fine in .NET 4, and should also work in .NET 3.5, although I have not tested it yet.

UPDATE:. does not work in the .NET Compact Framework (not even NETCF 3.7 for Windows Phone 7), because DataContractSerializer not supported!

I made the stream into a string because it was more convenient for me, although I could introduce lower level serialization for Stream and then use it to serialize for strings, but I tend to generalize only when necessary (as premature optimization is evil , so premature generalization ...)

Using is very simple:

 // dictionary to serialize to string Dictionary<string, object> myDict = new Dictionary<string, object>(); // add items to the dictionary... myDict.Add(...); // serialization is straight-forward string serialized = myDict.Serialize(); ... // deserialization is just as simple Dictionary<string, object> myDictCopy = serialized.Deserialize<Dictionary<string,object>>(); 

myDictCopy will be a verbatim copy of myDict.

You will also notice that the generic methods provided will be able to serialize any type (as far as I know), since it is not limited to IDictionary interfaces, it can really be any generic type T.

Hope this helps someone!

Answer 3

They added one in .NET 3.0. If possible, add a link to System.Runtime.Serialization and find System.Xml.XmlDictionary, System.Xml.XmlDictionaryReader and System.Xml.XmlDictionaryWriter.

I would agree that he is not in a particularly vulnerable place.

Answer 4

Create your own :-), the readonly function is a bonus, but if you need a key other than a line, then the class needs some modifications ...

 namespace MyNameSpace { [XmlRoot("SerializableDictionary")] public class SerializableDictionary : Dictionary<String, Object>, IXmlSerializable { internal Boolean _ReadOnly = false; public Boolean ReadOnly { get { return this._ReadOnly; } set { this.CheckReadOnly(); this._ReadOnly = value; } } public new Object this[String key] { get { Object value; return this.TryGetValue(key, out value) ? value : null; } set { this.CheckReadOnly(); if(value != null) { base[key] = value; } else { this.Remove(key); } } } internal void CheckReadOnly() { if(this._ReadOnly) { throw new Exception("Collection is read only"); } } public new void Clear() { this.CheckReadOnly(); base.Clear(); } public new void Add(String key, Object value) { this.CheckReadOnly(); base.Add(key, value); } public new void Remove(String key) { this.CheckReadOnly(); base.Remove(key); } public XmlSchema GetSchema() { return null; } public void ReadXml(XmlReader reader) { Boolean wasEmpty = reader.IsEmptyElement; reader.Read(); if(wasEmpty) { return; } while(reader.NodeType != XmlNodeType.EndElement) { if(reader.Name == "Item") { String key = reader.GetAttribute("Key"); Type type = Type.GetType(reader.GetAttribute("TypeName")); reader.Read(); if(type != null) { this.Add(key, new XmlSerializer(type).Deserialize(reader)); } else { reader.Skip(); } reader.ReadEndElement(); reader.MoveToContent(); } else { reader.ReadToFollowing("Item"); } reader.ReadEndElement(); } public void WriteXml(XmlWriter writer) { foreach(KeyValuePair<String, Object> item in this) { writer.WriteStartElement("Item"); writer.WriteAttributeString("Key", item.Key); writer.WriteAttributeString("TypeName", item.Value.GetType().AssemblyQualifiedName); new XmlSerializer(item.Value.GetType()).Serialize(writer, item.Value); writer.WriteEndElement(); } } } } 

Answer 5

Use DataContractSerializer! See Sample below.

 using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Runtime.Serialization; using System.Xml; namespace ConsoleApplication1 { class Program { static void Main(string[] args) { A a = new A(); a.Value = 1; B b = new B(); b.Value = "SomeValue"; Dictionary<A, B> d = new Dictionary<A,B>(); d.Add(a, b); DataContractSerializer dcs = new DataContractSerializer(typeof(Dictionary<A, B>)); StringBuilder sb = new StringBuilder(); using (XmlWriter xw = XmlWriter.Create(sb)) { dcs.WriteObject(xw, d); } string xml = sb.ToString(); } } public class A { public int Value { get; set; } } public class B { public string Value { get; set; } } } 

In the above code, the following xml is created:

 <?xml version="1.0" encoding="utf-16"?> <ArrayOfKeyValueOfABHtQdUIlS xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/2003/10/Serialization/Arrays"> <KeyValueOfABHtQdUIlS> <Key xmlns:d3p1="http://schemas.datacontract.org/2004/07/ConsoleApplication1"> <d3p1:Value>1</d3p1:Value> </Key> <Value xmlns:d3p1="http://schemas.datacontract.org/2004/07/ConsoleApplication1"> <d3p1:Value>SomeValue</d3p1:Value> </Value> </KeyValueOfABHtQdUIlS> </ArrayOfKeyValueOfABHtQdUIlS> 

Answer 6

This is my implementation.

 using System; using System.Collections.Generic; using System.Text; using System.Xml.Serialization; using System.Xml.Schema; using System.Xml; namespace Rubik.Staging { [XmlSchemaProvider("GetInternalSchema")] public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IXmlSerializable { #region IXmlSerializable Members private const string ns = "http://www.rubik.com.tr/staging"; public static XmlQualifiedName GetInternalSchema(XmlSchemaSet xs) { bool keyIsSimple = (typeof(TKey).IsPrimitive || typeof(TKey) == typeof(string)); bool valueIsSimple = (typeof(TValue).IsPrimitive || typeof(TValue) == typeof(string)); XmlSchemas schemas = new XmlSchemas(); XmlReflectionImporter importer = new XmlReflectionImporter(ns); importer.IncludeType(typeof(TKey)); importer.IncludeType(typeof(TValue)); XmlTypeMapping keyMapping = importer.ImportTypeMapping(typeof(TKey)); XmlTypeMapping valueMapping = importer.ImportTypeMapping(typeof(TValue)); XmlSchemaExporter exporter = new XmlSchemaExporter(schemas); if(!keyIsSimple) exporter.ExportTypeMapping(keyMapping); if(!valueIsSimple) exporter.ExportTypeMapping(valueMapping); XmlSchema schema = (schemas.Count == 0 ? new XmlSchema() : schemas[0]); schema.TargetNamespace = ns; XmlSchemaComplexType type = new XmlSchemaComplexType(); type.Name = "DictionaryOf" + keyMapping.XsdTypeName + "And" + valueMapping.XsdTypeName; XmlSchemaSequence sequence = new XmlSchemaSequence(); XmlSchemaElement item = new XmlSchemaElement(); item.Name = "Item"; XmlSchemaComplexType itemType = new XmlSchemaComplexType(); XmlSchemaSequence itemSequence = new XmlSchemaSequence(); XmlSchemaElement keyElement = new XmlSchemaElement(); keyElement.Name = "Key"; keyElement.MaxOccurs = 1; keyElement.MinOccurs = 1; XmlSchemaComplexType keyType = new XmlSchemaComplexType(); XmlSchemaSequence keySequence = new XmlSchemaSequence(); XmlSchemaElement keyValueElement = new XmlSchemaElement(); keyValueElement.Name = keyMapping.ElementName; keyValueElement.SchemaTypeName = new XmlQualifiedName(keyMapping.XsdTypeName, keyMapping.XsdTypeNamespace); keyValueElement.MinOccurs = 1; keyValueElement.MaxOccurs = 1; keySequence.Items.Add(keyValueElement); keyType.Particle = keySequence; keyElement.SchemaType = keyType; itemSequence.Items.Add(keyElement); XmlSchemaElement valueElement = new XmlSchemaElement(); valueElement.Name = "Value"; valueElement.MaxOccurs = 1; valueElement.MinOccurs = 1; XmlSchemaComplexType valueType = new XmlSchemaComplexType(); XmlSchemaSequence valueSequence = new XmlSchemaSequence(); XmlSchemaElement valueValueElement = new XmlSchemaElement(); valueValueElement.Name = valueMapping.ElementName; valueValueElement.SchemaTypeName = new XmlQualifiedName(valueMapping.XsdTypeName, valueMapping.XsdTypeNamespace); valueValueElement.MinOccurs = 1; valueValueElement.MaxOccurs = 1; valueSequence.Items.Add(valueValueElement); valueType.Particle = valueSequence; valueElement.SchemaType = valueType; itemSequence.Items.Add(valueElement); itemType.Particle = itemSequence; item.SchemaType = itemType; sequence.Items.Add(item); type.Particle = sequence; schema.Items.Add(type); xs.XmlResolver = new XmlUrlResolver(); xs.Add(schema); return new XmlQualifiedName(type.Name, ns); } public void ReadXml(System.Xml.XmlReader reader) { XmlSerializer keySerializer = new XmlSerializer(typeof(TKey)); XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue)); bool wasEmpty = reader.IsEmptyElement; reader.Read(); if (wasEmpty) return; while (reader.NodeType != System.Xml.XmlNodeType.EndElement) { reader.ReadStartElement("Item"); reader.ReadStartElement("Key"); TKey key = (TKey)keySerializer.Deserialize(reader); reader.ReadEndElement(); reader.ReadStartElement("Value"); TValue value = (TValue)valueSerializer.Deserialize(reader); reader.ReadEndElement(); this.Add(key, value); reader.ReadEndElement(); reader.MoveToContent(); } reader.ReadEndElement(); } public void WriteXml(System.Xml.XmlWriter writer) { XmlSerializer keySerializer = new XmlSerializer(typeof(TKey)); XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue)); foreach (TKey key in this.Keys) { writer.WriteStartElement("Item"); writer.WriteStartElement("Key"); keySerializer.Serialize(writer, key); writer.WriteEndElement(); writer.WriteStartElement("Value"); TValue value = this[key]; valueSerializer.Serialize(writer, value); writer.WriteEndElement(); writer.WriteEndElement(); } } #endregion #region IXmlSerializable Members public XmlSchema GetSchema() { return null; } #endregion } } 

Answer 7

General helper for quickly adding IXmlSerializable to any (existing) dictionary without using inheritance:

 using System.Xml; using System.Xml.Serialization; using System.Collections.Generic; namespace GameSpace { public class XmlSerializerForDictionary { public struct Pair<TKey,TValue> { public TKey Key; public TValue Value; public Pair(KeyValuePair<TKey,TValue> pair) { Key = pair.Key; Value = pair.Value; }//method }//struct public static void WriteXml<TKey,TValue>(XmlWriter writer, IDictionary<TKey,TValue> dict) { var list = new List<Pair<TKey,TValue>>(dict.Count); foreach (var pair in dict) { list.Add(new Pair<TKey,TValue>(pair)); }//foreach var serializer = new XmlSerializer(list.GetType()); serializer.Serialize(writer, list); }//method public static void ReadXml<TKey, TValue>(XmlReader reader, IDictionary<TKey, TValue> dict) { reader.Read(); var serializer = new XmlSerializer(typeof(List<Pair<TKey,TValue>>)); var list = (List<Pair<TKey,TValue>>)serializer.Deserialize(reader); foreach (var pair in list) { dict.Add(pair.Key, pair.Value); }//foreach reader.Read(); }//method }//class }//namespace 

And a convenient serializable general dictionary:

 using System.Xml; using System.Xml.Schema; using System.Xml.Serialization; using System.Collections.Generic; namespace GameSpace { public class SerializableDictionary<TKey,TValue> : Dictionary<TKey,TValue>, IXmlSerializable { public virtual void WriteXml(XmlWriter writer) { XmlSerializerForDictionary.WriteXml(writer, this); }//method public virtual void ReadXml(XmlReader reader) { XmlSerializerForDictionary.ReadXml(reader, this); }//method public virtual XmlSchema GetSchema() { return null; }//method }//class }//namespace 

Answer 8

I know that now it was done to death, but here is my contribution. I took the good bits from the solutions from @Loudenvier and @Jack and wrote my own serializable (sorry, I'm British) dictionary.

 public class SerialisableDictionary<T1, T2> : Dictionary<T1, T2>, IXmlSerializable { private static DataContractSerializer serializer = new DataContractSerializer(typeof(Dictionary<T1, T2>)); public void WriteXml(XmlWriter writer) { serializer.WriteObject(writer, this); } public void ReadXml(XmlReader reader) { Dictionary<T1, T2> deserialised = (Dictionary<T1, T2>)serializer.ReadObject(reader); foreach(KeyValuePair<T1, T2> kvp in deserialised) { Add(kvp.Key, kvp.Value); } } public XmlSchema GetSchema() { return null; } } 

I like this approach because you don’t have to explicitly serialize or deserialize anything, just pump the entire class hierarchy through the XmlSerializer and you're done.