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C# - Serializing List of Object to XML using generic method [duplicate]

I have a serializable class and one of the properties in my class generates a Guid in the getter. The property implements no setter and is ignores during serialization. Why is that and do I always have to implement a setter in order for my property to be serialized.
[Serializable]
public class Example
{
[XmlAttribute("id")]
public string Id
{
get
{
return Guid.NewGuid().ToString();
}
}
}
I tried implementing an empty setter and it got serialized correctly.
[Serializable]
public class Example
{
[XmlAttribute("id")]
public string Id
{
get
{
return Guid.NewGuid().ToString();
}
set {}
}
}
Update:
Can you point out how should I define properties whose values never change or ones that the value for is generated internally?

It's a limitation of XmlSerializer it doesn't serialize read-only properties, what you have done in your second example is essentially the hack to get it to serialize, however, it's useless if you need it to deserialize later.
Alternatively you could switch to using DataContractSerializer, it's more flexible.

See "Introducing XML Serialization" in the MSDN documentation. Among other things, it says:
Items That Can Be Serialized
The following items can be serialized using the XmlSerializer class:
Public read/write properties and fields of public classes.
Classes that implement ICollection or IEnumerable.
Note:
Only collections are serialized, not public properties.
XmlElement objects.
XmlNode objects.
DataSet objects.
Also, see "Why XML-Serializable class need a parameterless constructor"
Also, IXmlSerializable
In addition to the above types which can be serialized by the XML Serializer, any type which implements the IXmlSerializable interface can be serialized and deserialized. In particular, this means that the XElement and XDocument types can be serialized.
See "IXmlSerializable Interface".

Limitation of XMLSerializer - Properties without setter can't be serialized.
But you can use DataContractSerializer to serialize private setter properties -
[DataMember]
public string Id
{
get
{
return Guid.NewGuid().ToString();
}
private set {}
}

if you want to have private setters, and have the object be serializable/deserializable, impliment ISerializable, and create a constructor like MyObject(SerializationInfo info, StreamingContext context). An example is found here.

Serialization attributes are used to serialize and deserialize objects.
XmlSerializer will assume that you don't need to serialize any property that doesn't have a setter.
Setter will be used when deserializing a string into an object, because an instance of the object needs to be created and then the setter will be used to populate the property value.

NetDataContractSerializer Deserialization With New Property

Lacking any real foresight, I've serialized a large set of data decorated only with Serializable using NetDataContractSerializer, and now I'd like to add a new field. What are my options?
The original class looks something like this (with a few levels of inheritance and quite a few fields):
[Serializable]
public class InheritedClass : BaseClass
{
public string StringId { get; set; }
}
And now I'd like to add another property, say something like:
[Serializable]
public class InheritedClass : BaseClass
{
public string StringId { get; set; }
public int IntId { get; set; }
}
Now when I update the class and go to deserialize, I receive an exception since the new field is not present, something like:
Exception thrown: 'System.Runtime.Serialization.SerializationException' in System.Runtime.Serialization.dll
Additional information: Error in line 1 position 601. 'Element' '_x003C_StringId_x003E_k__BackingField' from namespace 'http://schemas.datacontract.org/2004/07/QT' is not expected. Expecting element '_x003C_IntId_x003E_k__BackingField'.
Ok, so this makes sense since NetDataContractSerializer requires the same class. I can get around that using a DataMember attribute like:
[DataMember(IsRequired = false)]
The problem then is that switching to DataMember (as I should have done upfront, or used a different serializer) changes the implicit alphabetical ordering, and then most of my fields will silently not deserialize as is well known.
I've attempted to add an ordering that's inline with the ordering on disk manually (via Order properties on the attribute), but that doesn't appear to be respected either. (I don't see an order value I could match in the raw xml either.)
Are there any other options beyond writing something to load the xml and insert the missing node? (Or equivalently setup a parallel type and deserialize from one an re-serialize to another?) If not, I'll probably just load up with the current type and deserialize to JsonNet or protobuf, but am I missing anything more straightforward with DataMember/etc?

Marking a type with [Serializable] means that the type can be serialized by serializing its public and private fields -- not its properties. NetDataContractSerializer respects this attribute when present, serializing the fields as indicated. For an auto-implemented property the secret backing field is what is actually serialized.
When adding a new field, what one generally does to handle legacy data is to mark it with [OptionalField] to indicate that it won't always be present in serialization streams. In c# 7.3 and later, it's possible to do this to the secret backing field of an auto-implemented property by using a field-targeted attribute:
[Serializable]
public class InheritedClass : BaseClass
{
public string StringId { get; set; }
[field: OptionalField]
public int IntId { get; set; }
}
Prior to c# 7.3 there is no way to apply an attribute to the backing field of an auto-implemented property. Thus you need to make the backing field be explicit and add the attribute to it:
[Serializable]
public class InheritedClass : BaseClass
{
public string StringId { get; set; }
[OptionalField]
int intId;
public int IntId { get { return intId; } set { intId = value; } }
}
Notes:
As noted in the question, if a type is marked with data contract attributes then NetDataContractSerializer will use those in preference to the default [Serializable] contract and allow you to explicitly indicate properties to serialize (and provide names clearer than the secret backing field names).
Unfortunately it is not always practical to add data contract attributes to legacy types.
NetDataContractSerializer has not been ported to .NET Core / .NET 5 and likely never will be.

Force WCF to serialize unused class

I appear to be having an issue with the following snippet of code in that, when I come to specifying what the Item is (eg CashInHand), the actual type CashInHandPayment is not available because it hasn't been carried across when I generate the proxy class (most likely because it doesn't read in XmlElementAttributes).
Is there any way to force classes such as AccountPayment, CashInHandPayment and CCPayment to be serialized in the proxy class?
[DataContract]
public class Payment
{
[XmlElementAttribute("Account", typeof(AccountPayment))]
[XmlElementAttribute("CashInHand", typeof(CashInHandPayment))]
[XmlElementAttribute("CreditCard", typeof(CCPayment))]
[XmlChoiceIdentifierAttribute("ItemElementName")]
[DataMember]
public object Item { get; set; }
}
[DataContract]
public enum ItemElementName
{
[EnumMember]
Account,
[EnumMember]
CashInHand,
[EnumMember]
CreditCard
}
//This class will not be in the generated proxy class
[DataContract]
public class AccountPayment
{
[DataMember]
public double Amount { get; set; }
}
//classes for CashInHandPayment and CCPayment also created, but not shown.
Forgive me if 'serialize' isn't the correct term to use, if you read the question and find that it isn't, please change it accordingly!
Update - answer mentioned by Simon Svensson:
[KnownType(typeof(AccountPayment))]
[KnownType(typeof(CashInHandPayment))]
[KnownType(typeof(CCPayment))]
[DataContract]
public class Payment
{
[XmlElementAttribute("Account", typeof(AccountPayment))]
[XmlElementAttribute("CashInHand", typeof(CashInHandPayment))]
[XmlElementAttribute("CreditCard", typeof(CCPayment))]
[XmlChoiceIdentifierAttribute("ItemElementName")]
[DataMember]
public object Item { get; set; }
}
Many thanks, Simon!

Uhm. Isnt XmlElementAttribute and XmlChoiceIdentifierAttribute xml serialization, which is a older serialization compared to the DataContractSerializer which reads DataContractAttribute and DataMemberAttribute?
I believe that you should use the KnownTypeAttribute for this, but I have never tried it, nor have I had this scenario in my own code.

Is there any way to force classes such as AccountPayment,
CashInHandPayment and CCPayment to be serialized in the proxy class?
They need to be marked with a [DataContract] attribute, that should be sufficient, I would think.
When svcutil.exe (either launched directly from the command line, or from Visual Studio using Add Service Reference) encounters classes with the [DataContract] attribute on the class and [DataMember] on the properties (or fields), it will create a copy in the proxy for those classes.
Marc

I think specifying DataContract should be sufficient. But, if that isn't working, why not try creating a dummy OperationContract method that uses the class?

Using XmlIgnore on generated partial classes

I've got a LINQ 2 SQL generated class I'd like to expose through a webservice.
There are some internal properties I don't want to be available.
Normally I'd throw [XmlIgnore] in there but because the properties are in the generated half I can't do that.
I've been looking at using MetadataType following this post which looks like it should allow me to define the property attributes in another class.
My code looks something like this:
[MetadataType(typeof(ProspectMetaData))]
public partial class Prospect : ApplicationBaseObject
{
}
public class ProspectMetaData
{
[XmlIgnore]
public object CreatedDateTime { get; set; }
[XmlIgnore]
public object AmendedDateTime { get; set; }
[XmlIgnore]
public object Timestamp { get; set; }
}
I'm referencing this through an ASP.NET Web Service from a Silverlight Project.
The issue is that the [XmlIgnore] attributes are being ignored, those properties are being sent through.
Does anyone have any insight into what might be going wrong here? and what might be the best way to do this?

You can do this by passing your own XmlAttributeOverrides to the XmlSerializer, in the XmlAttributeOverrides you can change the XmlIgnore to true for the fields/properties you wish without touching the DBML generated code and it works like a charm, use the same overrides to deserialize as well...
Refer this link for more information
// Create the XmlAttributeOverrides and XmlAttributes objects.
XmlAttributeOverrides xOver = new XmlAttributeOverrides();
XmlAttributes attrs = new XmlAttributes();
attrs.XmlIgnore = true;
/* Setting XmlIgnore to true overrides the XmlIgnoreAttribute
applied to the following fields. Thus it will be serialized.*/
xOver.Add(typeof(Prospect), "CreatedDateTime", attrs);
xOver.Add(typeof(Prospect), "AmendedDateTime", attrs);
xOver.Add(typeof(Prospect), "Timestamp", attrs);
XmlSerializer xSer = new XmlSerializer(typeof(Prospect), xOver);
TextWriter writer = new StreamWriter(outputFilePath);
xSer.Serialize(writer, object);

AFAIK, MetadataTypeAttribute is not supported by XmlSerializer (although it would be nice - I've simply never checked). And as you say, you can't add member attributes in a partial class.
One option may be to make the generated properties non-public (private, protected or internal) - and name it something like TimestampStorage (etc) - then re-expose them (in the partial class) on the public API:
[XmlIgnore]
public object Timestamp {
get {return TimestampStorage; }
set {TimestampStorage = value; }
}
// and other properties
(since XmlSerializer only looks at the public API). The biggest problem here is that LINQ-to-SQL queries (Where etc) will only work against the generated columns (TimestampStorage etc). I've used this approach before with the member as internal, allowing my DAL class to use the internal property... but it is a bit of a fudge.

I agree with Marc. The easiest thing to do is mark them internal. Optionally, you can then re-expose them in the partial class with [XmlIgnore]. BTW, You can control the accessibility of the properties in the linq2sql designer. Get at the properties dialog and you'll see a place to set them

Calling GetObjectData on serialization

I am confused about the serialization sample from MSDN.
My confusion is in method GetObjectData (which is called during serialization), will the method,
serialize both the additional data (in method GetObjectData from AddValue) and the fields/properties of the class;
or just write the data in method GetObjectData without writing fields/properties of the class?
I have debugged seems (2) is correct -- no fields/properties data are serialized if GetObjectData method is used? Is that correct? (I am not an expert and just want to confirm here, but 100% confident about myself.)

Im not sure what you want to achieve but isn't easier to let C# do the work for you:
using System;
using System.Collections.Generic;
using System.Xml.Serialization;
namespace Test
{
[Serializable]
public class TestObject
{
private String name;
private String note;
#region Getters/setters
public String Name
{
get { return name; }
set { name = value; }
}
public String Note
{
get { return note; }
set { note = value; }
}
#endregion
}
}
Now you can use the XmlSerializer or BinaryFormatter to (de)serialize the object

If you implement ISerializable, you are reasponsible for all data (i.e. scenario "2" in your question); nothing extra is serialized automatically. What is your requirement? Things like DataContractSerializer can be property-based, allowing you to decorate both the regular fields and your custom property (that has some logic) and have them serialized properly. If you need binary (for space etc), then perhaps consider things like protobuf-net, which mixes the two while being space efficient.
So: what are your requirements?
Data Contract example:
[DataContract]
public class Foo {
[DataMember]
public int Bar {get;set;} // simple data
[DataMember]
private string DoSomeThinking {
get {.... serialize the complex data ....}
set {.... deserialize the complex data ....}
}
}

If you implement ISerializable you must add all data (at least the data needed to deserialize) including all fields to the SerializationInfo using AddValue.