I am attempting to serialise some records into CSV using the ServiceStack.Text library.
I am using inheritance, specifically abstract classes and the properties on the child types are not being output. Yes I know this is a bad idea but as I have no need to deserialise the types and I'm not making a public API. Regardless, this scenario seems to be supported by the docs.
For this example:
public abstract class ResultBase
{
public int MinuteOffset { get; set; }
public double SegmentDuration { get; set; }
}
public class EventIndex : IndexBase
{
public int EventsTotal { get; set; }
public int EventsTotalThresholded { get; set; }
}
And the code to serialise:
var destination = new FileInfo("C:\\somefile.txt")
using (var stream = destination.CreateText())
{
JsvStringSerializer s = new JsvStringSerializer();
var o = s.SerializeToString(results);
stream.Write(o);
CsvSerializer.SerializeToWriter(results, stream);
}
The CSV serialiser outputs this (not what I want):
MinuteOffset,SegmentDuration
0,0
But, the JSV serialiser seems to behave as expected:
[{__type:"AnalysisBase.EventIndex, AnalysisBase",EventsTotal:0,EventsTotalThresholded:0,MinuteOffset:0,SegmentDuration:0}]
Why are there differences in the fields output, is there anyway I can get the CSV serialiser to output all child properties?
The CsvSerializer.SerializeToWriter is a generic method which is not operating on the runtime type of the object. If you are calling for serialization through a base type of the current instance then the serializer will not now any other properties then the base one's.
public static void SerializeToWriter<T>(T value, TextWriter writer)
{
if (value == null) return;
if (typeof(T) == typeof(string))
{
writer.Write(value);
return;
}
CsvSerializer<T>.WriteObject(writer, value);
}
Related
Given the following XML I want to deserialize:
<?xml version="1.0" encoding="utf-8" ?>
<units>
<entity>
<health max="1000"/>
<sprite texture="tank"/>
<entity>
<sprite texture="tank-turret"/> <!-- this element is missing when i deserialize --!>
</entity>
</entity>
</units>
How can I deserialize this recursive object graph using XmlSerializer?
The following is my last try. It successfully deserializes the top-level objects (health, sprite, entity) but it does not seem to find the sprite element in the nested entity node.
I also tried deriving entity from componentlist, but it didn't work either.
public class UnitSerializer
{
public abstract class item
{
}
public class entity : item
{
[XmlArray("entity")]
[XmlArrayItem(typeof(health))]
[XmlArrayItem(typeof(entity))]
[XmlArrayItem(typeof(sprite))]
public componentlist entity2 { get; set; }
}
public abstract class component : item
{
}
public class health : component
{
[XmlAttribute]
public int max { get; set; }
}
public class sprite : component
{
[XmlAttribute]
public string texture { get; set; }
}
public class componentlist : List<item>
{
}
[XmlRoot("units")]
public class units
{
[XmlArray("entity")]
[XmlArrayItem(typeof(health))]
[XmlArrayItem(typeof(entity))]
[XmlArrayItem(typeof(sprite))]
public componentlist entity { get; set; }
}
public void Read()
{
var x = new XmlSerializer(typeof(units),
new[] {
typeof(componentlist),
typeof(entity),
typeof(health),
typeof(sprite)
});
var fs = new FileStream("units.xml", FileMode.Open);
XmlReader reader = new XmlTextReader(fs);
var units = (units)x.Deserialize(reader);
}
}
Your classes can be fixed by replacing use of [XmlArray] and [XmlArrayItem] with [XmlElement(typeof(TDerived))]:
public class UnitSerializer
{
public abstract class item
{
}
public class entity : item
{
[XmlElement("health", typeof(health))]
[XmlElement("entity", typeof(entity))]
[XmlElement("sprite", typeof(sprite))]
public List<item> EntityList { get; set; }
}
public abstract class component : item
{
}
public class health : component
{
[XmlAttribute]
public int max { get; set; }
}
public class sprite : component
{
[XmlAttribute]
public string texture { get; set; }
}
[XmlRoot("units")]
public class units
{
[XmlElement("health", typeof(health))]
[XmlElement("entity", typeof(entity))]
[XmlElement("sprite", typeof(sprite))]
public List<item> EntityList { get; set; }
}
public units Read(string filename)
{
var x = new XmlSerializer(typeof(units));
using (var fs = new FileStream(filename, FileMode.Open))
using (var reader = XmlReader.Create(fs))
{
return (units)x.Deserialize(reader);
}
}
}
Notes:
[XmlArray] indicates a collection should be serialized with an outer wrapper element containing a sequence of elements, while [XmlElement] indicates a collection should be serialized as a sequence without the wrapper. Your XML sample uses repeating elements without wrapper elements, so [XmlElement] should be used. It sort of works because your XML is recursive -- but at every other level repeating elements are getting incorrectly deserialized as wrappers. This explains why some but not all data is lost during deserialization.
In your XML sample, polymorphic elements are identified by element name. The XmlSerializer(Type, Type[]) constructor should be used to specify polymorphic included types to be serialized using the xsi:type mechanism. Since the xsi:type attribute does not appear in your XML, this constructor need not be used.
(In addition, when constructing an XmlSerializer using the XmlSerializer(Type, Type[]) constructor, you must cache the serializer statically to avoid a severe memory leak. See Memory Leak using StreamReader and XmlSerializer for why.)
XmlTextReader has been deprecated since .Net 2.0. Use XmlReader.Create() instead.
The FileStream and XmlReader should be disposed, ideally via using statements.
I eliminated the public class componentlist : List<item> and replaced it with just a List<item>. This was mainly a matter of taste, but it does make it easier to set the value of such a list using Linq's .ToList().
Demo fiddle here.
I have a project with about 200 classes which need to be saved as json and deserialized back later.
All the classes are immutable and due to this fact I need to inject all complex types into the constructor, otherwise deserialization does not work. Because I use a Clonable base class I don't initialize every parameter in the constructor. When I forget to add a single class to the construtor or misspell it, deserialization does not work anymore and the only way I know to check is to write a lot of unit tests with sample data.
This is a sample to reproduce my problem:
static void Main(string[] args)
{
var immutableClass = new ImmutableClass(new OtherImmutableClass(2)).WithAnyProperty(1);
var jsonString = JsonConvert.SerializeObject(immutableClass, Formatting.Indented);
var deserializedObject = JsonConvert.DeserializeObject<ImmutableClass>(jsonString);
}
public class ImmutableClass : Clonable<ImmutableClass>
{
public ImmutableClass(OtherImmutableClass otherImmutableClassInstance)
{
OtherImmutableClassInstance = otherImmutableClassInstance;
}
public OtherImmutableClass OtherImmutableClassInstance { get; }
[JsonProperty]
public int AnyProperty { get; private set; }
public ImmutableClass WithAnyProperty(int newValue)
{
return With(s => s.AnyProperty = newValue);
}
}
public class OtherImmutableClass
{
public OtherImmutableClass(int completelyWrongPropertyName)
{
MyProperty = completelyWrongPropertyName;
}
public int MyProperty { get; }
}
public abstract class Clonable<T> where T : Clonable<T>
{
protected T With(Action<T> updateAction)
{
var clone = (T)MemberwiseClone();
updateAction(clone);
return clone;
}
}
After serialization the content of my jsonString is as expected:
{
"OtherImmutableClassInstance": {
"MyProperty": 2
},
"AnyProperty": 1
}
When I deserialize no Exception is thrown but the MyProperty is 0 instead of 2 because of completelyWrongPropertyName does not match MyProperty in the constructor of OtherImmutableClass.
Is there an easy way to check if my model is serializable and deserializable without writing UnitTests for each class?
I am searching something like JsonChecker<ImmutableClass>.CanSerializeAndDeserialize();
I already asked google but found no solution.
I realize this looks to be an exact duplicate of Using XmlSerializer to serialize derived classes, but I cannot figure out how to get this working following the guidance from that same question:
using System;
using System.Text;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;
namespace xmlSerializerLab
{
public class Utf8StringWriter : System.IO.StringWriter
{
public override Encoding Encoding => Encoding.UTF8;
}
[XmlRoot(ElementName = "Query", Namespace = "http://www.opengis.net/wfs")]
public class Query
{
[XmlElement(ElementName = "Filter", Namespace = "http://www.opengis.net/ogc")]
public Filter Filter { get; set; }
}
[XmlInclude(typeof(PropertyIsOpFilter))]
[XmlInclude(typeof(PropertyIsEqualToFilter))]
[XmlInclude(typeof(OpFilterBase))]
[XmlInclude(typeof(LiteralFilter))]
[XmlInclude(typeof(Query))]
[Serializable]
public class Filter
{
[XmlElement]
public Filter And { get; set; }
}
public class PropertyIsOpFilter : Filter, IXmlSerializable
{
public Filter LeftOp { get; set; }
public Filter RightOp { get; set; }
public XmlSchema GetSchema()
{
return null;
}
public void ReadXml(XmlReader reader) { }
public void WriteXml(XmlWriter writer)
{
Program.ToXml(LeftOp, writer);
Program.ToXml(RightOp, writer);
}
}
[XmlRoot("IsEqualTo")]
public class PropertyIsEqualToFilter : PropertyIsOpFilter { }
public class OpFilterBase : Filter, IXmlSerializable
{
public string Op { get; set; }
public object Value { get; set; }
public XmlSchema GetSchema()
{
return null;
}
public void ReadXml(XmlReader reader) { }
public void WriteXml(XmlWriter writer)
{
if (!String.IsNullOrEmpty(Op))
{
writer.WriteStartElement(Op);
writer.WriteValue(Value);
writer.WriteEndElement();
}
else
{
writer.WriteValue(Value);
}
}
}
public class LiteralFilter : OpFilterBase { }
class Program
{
public static void ToXml(Object o, XmlWriter writer)
{
var inputSerializer = new XmlSerializer(o.GetType(), new Type[] {
typeof(Filter),
typeof(PropertyIsOpFilter),
typeof(PropertyIsEqualToFilter),
typeof(OpFilterBase),
typeof(LiteralFilter),
typeof(Query)
});
inputSerializer.Serialize(writer, o);
}
public static string ToXml(Object o)
{
var inputSerializer = new XmlSerializer(o.GetType());
using (var writer = new Utf8StringWriter())
{
using (var xmlWriter = new XmlTextWriter(writer))
{
ToXml(o, xmlWriter);
}
return writer.ToString();
}
}
static void Main(string[] args)
{
Filter o = new PropertyIsEqualToFilter()
{
LeftOp = new LiteralFilter()
{
Value = 1
},
RightOp = new LiteralFilter()
{
Value = 1
}
};
var query = new Query()
{
Filter = o
};
Console.WriteLine(ToXml(query));
Console.ReadLine();
}
}
}
It results in this exception:
InvalidOperationException: The type
xmlSerializerLab.PropertyIsEqualToFilter may not be used in this
context. To use xmlSerializerLab.PropertyIsEqualToFilter as a
parameter, return type, or member of a class or struct, the parameter,
return type, or member must be declared as type
xmlSerializerLab.PropertyIsEqualToFilter (it cannot be object).
Objects of type xmlSerializerLab.PropertyIsEqualToFilter may not be
used in un-typed collections, such as ArrayLists.
As far as I can tell, I need the IXmlSerializable on the PropertyIsOpFilter and OpFilterBase because I'm trying to target a specific XML format described by this schema. But I'm finding that I also have to make the Query class IXmlSerializable.
Here is a sample XML document that I'd like to be able to produce from the model:
<GetFeature xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"
service="WFS"
version="1.1.0"
maxFeatures="0" xmlns="http://www.opengis.net/wfs">
<ResultType>Results</ResultType>
<OutputFormat>text/gml; subtype=gml/3.1.1</OutputFormat>
<Query
d2p1:srsName="EPSG:4326" xmlns:d2p1="http://www.opengis.net/ogc">
<d2p1:Filter>
<d2p1:IsEqualTo>
<d2p1:PropertyName>Prop1</d2p1:PropertyName>
<d2p1:Literal>1</d2p1:Literal>
</d2p1:IsEqualTo>
</d2p1:Filter>
</Query>
</GetFeature>
By making the Query class IXmlSerializable and writing a good bit of WriteXml and ReadXml logic I can get it to work, but I'd expect it to work without having to do all that since the XmlRoot and XmlAttribute and XmlElement tags should give enough information to the serializer for it to know which class to instantiate based on the tag name (match ElementName) and certainly how to serialize based on the attributes.
The problem you are seeing can be reproduced with the following minimal example:
public class BaseClass
{
}
public class DerivedClass : BaseClass, IXmlSerializable
{
#region IXmlSerializable Members
public XmlSchema GetSchema() { return null; }
public void ReadXml(XmlReader reader) { throw new NotImplementedException(); }
public void WriteXml(XmlWriter writer) { }
#endregion
}
Using the serialization code:
BaseClass baseClass = new DerivedClass();
using (var textWriter = new StringWriter())
{
using (var xmlWriter = XmlWriter.Create(textWriter))
{
var serializer = new XmlSerializer(typeof(BaseClass), new Type[] { typeof(DerivedClass) });
serializer.Serialize(xmlWriter, baseClass);
}
Console.WriteLine(textWriter.ToString());
}
The following exception is thrown (sample fiddle #1):
System.InvalidOperationException: There was an error generating the XML document.
---> System.InvalidOperationException: The type DerivedClass may not be used in this context. To use DerivedClass as a parameter, return type, or member of a class or struct, the parameter, return type, or member must be declared as type DerivedClass (it cannot be object). Objects of type DerivedClass may not be used in un-typed collections, such as ArrayLists.
This is among the most unhelpful exception messages I have seen from XmlSerializer. To understand the exception, you need to understand how XmlSerializer handles polymorphism via the [XmlInclude] mechanism. If I remove IXmlSerializable from DerivedClass, the following XML is generated (fiddle #2):
<BaseClass xsi:type="DerivedClass" />
Notice the xsi:type type attribute? That is a w3c standard attribute that XmlSerializer uses to explicitly assert the type of a polymorphic element; it is documented here. When XmlSerializer is deserializing a polymorphic type to which [XmlInclude] attributes have been applied (either statically or through the constructor you are using), it will look for the xsi:type attribute to determine the actual type to construct and deserialize.
It is this, apparently, which conflicts with IXmlSerializable. A type which implements this interface should completely control its XML reading and writing. However, by parsing and interpreting the xsi:type attribute, XmlSerializer has already begun automatic deserialization, and so throws an exception due to the inconsistent deserialization strategies of the base and derived types.
What's more, adding IXmlSerializable to the base type doesn't really fix the problem either If you do so, the xsi:type attribute is never written, and later, when ReadXml() is called, an object of the base type will get unconditionally constructed, as shown in fiddle #3.
(It's conceivable that Microsoft could have implemented a special case where XmlSerializer begins automatic deserialization, then "backs off" and hands the task over to ReadXml() when an IXmlSerializable polymorphic type is encountered and constructed. But, they did not.)
The solution would seem to be to serialize your Filter types automatically using the [XmlInclude] mechanism. In fact I don't see any reason you need to use IXmlSerializable, and was able to serialize your model successfully by removing IXmlSerializable completely and making some minor changes to namespaces:
public static class XmlNamespaces
{
public const string OpengisWfs = "http://www.opengis.net/wfs";
}
[XmlRoot(Namespace = XmlNamespaces.OpengisWfs)]
public class Query
{
public Filter Filter { get; set; }
}
[XmlInclude(typeof(PropertyIsOpFilter))]
[XmlInclude(typeof(OpFilterBase))]
[XmlRoot(Namespace = XmlNamespaces.OpengisWfs)]
public class Filter
{
[XmlElement]
public Filter And { get; set; }
}
[XmlInclude(typeof(PropertyIsEqualToFilter))]
[XmlRoot(Namespace = XmlNamespaces.OpengisWfs)]
public class PropertyIsOpFilter : Filter
{
public Filter LeftOp { get; set; }
public Filter RightOp { get; set; }
}
[XmlRoot("IsEqualTo", Namespace = XmlNamespaces.OpengisWfs)]
public class PropertyIsEqualToFilter : PropertyIsOpFilter { }
[XmlInclude(typeof(LiteralFilter))]
[XmlRoot(Namespace = XmlNamespaces.OpengisWfs)]
public class OpFilterBase : Filter
{
public string Op { get; set; }
public object Value { get; set; }
}
[XmlRoot(Namespace = XmlNamespaces.OpengisWfs)]
public class LiteralFilter : OpFilterBase { }
Notes:
For the [XmlInclude] mechanism to work, all the included types apparently must be in the same XML namespace as the base type. To ensure this I added [XmlRoot(Namespace = XmlNamespaces.OpengisWfs)] to all the Filter subtypes.
The [XmlInclude(typeof(DerivedType))] attributes can be added either to their immediate parent type or to the lowest common base type. In the code above I added the attributes to the immediate parent types so that members of an intermediate type could be serialized successfully, e.g.:
public class SomeClass
{
PropertyIsOpFilter IsOpFilter { get; set; }
}
Consider marking intermediate types that cannot be instantiated as abstract, e.g. public abstract class Filter. Consider marking types that are "most derived" as sealed, e.g. public sealed class LiteralFilter
If you use the new XmlSerializer(Type, Type []) constructor, you must statically cache the serializer to avoid a severe memory leak, as explained here. It's not necessary in my solution but you are using it in your question.
Sample fiddle #4 showing that the following XML is generated successfully:
<Query xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.opengis.net/wfs">
<Filter xsi:type="PropertyIsEqualToFilter">
<LeftOp xsi:type="LiteralFilter">
<Value xsi:type="xsd:int">1</Value>
</LeftOp>
<RightOp xsi:type="LiteralFilter">
<Value xsi:type="xsd:int">1</Value>
</RightOp>
</Filter>
</Query>
I have a class that I need to serialize/deserialize, and I'm half way there - I have serialization functional, resulting in the below XML. However, since I'm implementing IXmlSerializable myself, I'm uncertain what an implementation of ReadXml should look like, given that SomeGenericClass<T> was serialized using attribute-based flagging rather than an explicit implementation if IXmlSerializable
<?xml version="1.0" encoding="utf-16"?>
<FooContainer FooName="DoSomething">
<SomeGenericClassOfString xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Value="Foobar" Name="firstParam" Description="First Paramater Serialized" />
<SomeGenericClassOfInt32 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Value="10000" Name="nextParam" Description="Second Serialized parameter" />
</FooContainer>
Which I want to serialize back into an instance of:
public class FooContainer : IList<ISomeGenericClassBase>, IXmlSerializable
{
public string FooName {get;set;}
void IXmlSerializable.WriteXml(XmlWriter writer) {
var serializer = XmlSerializer.FromTypes(new Type[]{SomeGenericBaseClass})[0];
this
.Select(item=>SomeGenericClassBase.ConvertToMe(item))
.ToList()
.ForEach(item=>serializer.Serialize(writer, item));
}
// IList Implementation omitted - wraps a private List<ISomeGenericClassBase>
}
Where the list will contain instances along these lines:
public interface ISomeGenericClassBase
{
}
public interface ISomeGenericBaseClass<T> : ISomeGenericBaseClass
{
}
public class SomeGenericClassBase : ISomeGenericClassBase
{
public static SomeGenericClassBase ConvertToMe(ISomeGenericClassBase target) {
return new SomeGenericClassBase() {Property1 = target.Property1; Property2 = target.Property2}
}
public static ISomeGenericBaseClass ExpantToTyped(SomeGenericClassBase target) {
// Implementation omitted - converts a base class instance to a generic instance by working out the generic type from saved data and reconstructing
}
}
public class SomeGenericClass<T> : SomeGenericClassBase, ISomeGenericBaseClass<T>
{
[XmlAttribute]
public string Name {get;set;}
[XmlAttribute]
public string Description{get;set;}
[XmlAttribute]
public T Value {get;set;}
[XmlElement("")]
public T[] ValidOptions {get;set;}
}
EDIT: Expanded the implementation - realised as it was, it didn't illustrate the problem correctly
Core issue is that I want to be able to serialize items that only implement the interface, even if I only get back SomeGenericClassBase instances. Per the approach used in the ExpandToTyped method, I'm expecting consumers of the class to save sufficient data in their implementations that allow the resulting classes to be converted back into their original form as required. So yes, there's a loss of fidelity, but it's one I can live with in exchange for the flexibility of using a list of interfaces instead of a list of base classes.
One solution is to sidestep the issue (IXmlSerializable.ReadXml looks quite painful anyway, e.g. for collections). What I eventually did is scrap IXmlSerializable, and instead generate a class along the lines of the below.
Please note that whilst this approach works, it's currently quite error prone if the serializable instance is used for anything other than serialization - synchronization is maintained ONLY when SerializationTarget is set or retrieved. When it's set, we convert existing parameters to appropriate instances and add them to a serializable list. When it's retrieved, if it's null, we inflate from whatever was in the current value.
However, if FooContainer changes after the creation of this object, it won't maintain that synchronization and what gets serialized will be out of date. This is largely because I'm lazy and don't want to implement IList<SomeGenericClassBase> again to override the Add and Remove methods (though this would be the more robust approach).
public class FooContainerSerializable
{
public FooContainerSerializable() {}
public FooContainerSerializable(FooContainer serializationTarget)
{
this.SerializationTarget = serializationTarget;
}
[XmlIgnore]
public FooContainer SerializationTarget
{
get {
if (_SerializationTarget == null)
{
_SerializationTarget = new FooContainer();
// Copy across extant collection properties here
this.Parameters.ForEach(item=>_SerializationTarget.Add(item));
}
return _SerializationTarget;
}
set {
// Synchronize this entity's entries here
_SerializationTarget = value;
_SerializationTarget.ForEach(item=>this.Parameters.Add(item.Deflate()));
}
}
private FooContainer _SerializationTarget;
[XmlElement]
public string FooName {
get {return this.SerializationTarget.FooName;}
set {this.SerializationTarget.FooName = value;}
}
[XmlElement]
public List<SomeGenericClassBase> Parameters {
get {return _Parameters ?? (_Parameters = new List<SomeGenericClassBase>());}
set {_Parameters = value;}
}
}
Here is another option if you are willing to use an abstract class instead of an interface in your collection definition. You'd also need to declare all the derived types of SomeGenericClassBase using XmlInclude attributes. I'm thinking this wouldn't be too bad if there are just a handful of types you'd use with this class.
[XmlRoot(ElementName = "FooContainer")]
public class FooContainer : List<SomeGenericClassBase>
{
[XmlAttribute]
public string FooName { get; set; }
}
[XmlInclude(typeof(SomeGenericClass<string>))]
[XmlInclude(typeof(SomeGenericClass<int>))]
public abstract class SomeGenericClassBase
{
[XmlAttribute]
public string Name { get; set; }
[XmlAttribute]
public string Description { get; set; }
}
public class SomeGenericClass<T> : SomeGenericClassBase
{
[XmlAttribute]
public T Value { get; set; }
[XmlElement]
public T[] ValidOptions { get; set; }
}
class Class1
{
public static void Run()
{
var f = new FooContainer()
{
new SomeGenericClass<string> { Name = "firstParam", Description = "First Paramater Serialized", Value = "Foobar"},
new SomeGenericClass<int> { Name = "nextParam", Description = "Second Serialized parameter", Value = 10000 }
};
f.FooName = "DoSomething";
XmlSerializer serializer = new XmlSerializer(f.GetType());
StringBuilder sb = new StringBuilder();
// Serialize
using (StringWriter writer = new StringWriter(sb))
{
serializer.Serialize(writer, f);
}
Console.WriteLine(sb);
// Deserialize
using(StringReader reader = new StringReader(sb.ToString()))
{
FooContainer f2 = (FooContainer)serializer.Deserialize(reader);
}
}
}
This would serialize to the following XML:
<?xml version="1.0" encoding="utf-16"?>
<FooContainer xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<SomeGenericClassBase xsi:type="SomeGenericClassOfString" Name="firstParam" Description="First Paramater Serialized" Value="Foobar" />
<SomeGenericClassBase xsi:type="SomeGenericClassOfInt32" Name="nextParam" Description="Second Serialized parameter" Value="10000" />
</FooContainer>
Deserialization maintains full fidelity.
I have a problem on serializing a class to XML. I have created a sample code that runs an shows the error. The class I want to serialize named "ContentContainer", ContentContainer has a collection of items that its type is "ContentItemBase". because my requirements I implemented these classes as follow. but when the code reaches to the part if actual serialization call, serializer throws this exception :
The type UserQuery+SpecificContentItem was not expected. Use the
XmlInclude or SoapInclude attribute to specify types that are not
known statically.
I have searched on this problem but my requirements I can't implement the XmlInclude method that mentioned in exception message.
is there any solution (Design OR Implementation Tip) for this problem and similar problems?
CODE :
void Main()
{
var item = new SpecificContentItem{ Name = "Test", Value = "TestValue" , SpecificField="TestField"};
var container = new ContentContainer();
container.Items.Add(item);
container.Name = "Test Container";
XmlSerializer ser= new XmlSerializer(typeof(ContentContainer));
StringWriter writer = new StringWriter();
ser.Serialize(writer, container);
string result = writer.ToString();
}
public abstract class ContentItemBase
{
public abstract string Name {get; set;}
public abstract string Value {get; set;}
}
public class SpecificContentItem: ContentItemBase
{
public string SpecificField {get; set;}
public override string Name {get; set;}
public override string Value {get; set;}
}
public class ContentContainer
{
public ContentContainer()
{
Items = new ContentItemCollection();
}
public string Name {get;set;}
public ContentItemCollection Items{get; set;}
}
public class ContentItemCollection : IEnumerable<ContentItemBase>
{
public SpecificContentItem SpecificItem { get; set; }
public IEnumerator<ContentItemBase> GetEnumerator()
{
if (SpecificItem != null)
yield return SpecificItem;
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public void Add(Object obj)
{
if (obj is SpecificContentItem)
SpecificItem = (SpecificContentItem)obj;
}
}
Creating your serializer as:
XmlSerializer ser = new XmlSerializer(typeof(ContentContainer),
new Type[] { typeof(SpecificContentItem) });
should do the trick.
You can also add a Serialize method to ContentContainer class
public string Serialize()
{
var types = Items.Select(x => x.GetType()).Distinct().ToArray();
XmlSerializer ser = new XmlSerializer(typeof(ContentContainer),types);
StringWriter writer = new StringWriter();
ser.Serialize(writer, this);
return writer.ToString();
}
Since the allowed use of XmlInclude seems to be ambiguous, I'm still going to suggest
[XmlInclude(typeof(SpecificContentItem))]
public class ContentItemCollection : IEnumerable<ContentItemBase>
{
as a possible solution. How that applies with your real world situation is a bit more difficult to tell, but I hope it's applicable and works!