I'm trying to find a way to change the serialization behavior of a property.
Lets say I have a situation like this:
[Serializable]
public class Record
{
public DateTime LastUpdated {get; set; }
// other useful properties ...
}
public class EmployeeRecord : Record
{
public string EmployeeName {get; set; }
// other useful properties ...
}
Now I want to serialize EmployeeRecord. I don't want the LastUpdated property from the Record class to be serialized. (I do want LastUpdated to be serialized when I serialize Record, though).
First I tried hiding the LastUpdated property by using the new keyword and then adding the XmlIgnore attribute:
public class EmployeeRecord : Record
{
public string EmployeeName {get; set; }
[XmlIgnore]
public new DateTime LastUpdated {get; set; }
// other useful properties ...
}
But that didn't work. Then I tried making the base LastUpdated virtual and overriding it, keeping the attribute:
[Serializable]
public class Record
{
public virtual DateTime LastUpdated {get; set; }
// other useful properties ...
}
public class EmployeeRecord : Record
{
public string EmployeeName {get; set; }
[XmlIgnore]
public override DateTime LastUpdated {get; set; }
// other useful properties ...
}
This didn't work either. In both attempts the LastUpdated ignored the XmlIgnore attribute and happily went about its business of serializing.
Is there a way to make what I'm trying to do happen?
First, the [Serializable] attr has nothing to do with the XmlSerializer. That is a red herring. [Serializable] is meaningful to System.Runtime.Serialization, while the XmlSerializer lives in System.Xml.Serialization. If you are decorating your class with [Serializable] and your members with [XmlIgnore] then you are probably confusing yourself or other readers of your code.
XmlSerialization in .NET is very flexible. Depending on how the serialization is being done, directly by you or indirectly, let's say by the web services runtime - you have different ways to control things.
One option is to use the propertyNameSpecified pattern to turn ON or OFF the property in XML Serialization. Suppose you have this code:
public class TypeA
{
public DateTime LastModified;
[XmlIgnore]
public bool LastModifiedSpecified;
}
Then, if LastModifiedSpecified is false in an instance, the LastModified field will not be serialized for that instance. In the constructor for your type, you can set LastModifiedSpecified to always be true in the base type, and always false in the derived type. The actual boolean - LastModifiedSpecified - never gets serialized because it is marked XmlIgnore.
This little trick is documented here.
Your other option is to use XmlAttributeOverrides, which is a way of dynamically providing the set of XML serialization attributes (like XmlElementAttribute, XmlIgnoreAttribute, XmlRootAttribute, and so on...) - dynamically providing those attributes to the serializer at runtime. The XmlSerializer, instead of inspecting the type itself for those attributes, will just walk through the list of override attributes provided to its constructor.
var overrides = new XmlAttributeOverrides();
// ....fill the overrides here....
// create a new instance of the serializer specifying overrides
var s1 = new XmlSerializer(typeof(Foo), overrides);
// serialize as normal, here.
This is illustrated in more detail here.
In your case, you would provide an XmlIgnoreAttribute as an override, but only when serializing the derived type. (or whatever) This works only when you directly instantiate the XmlSerializer - it won't work when serialization is done implicitly by the runtime, as with web services.
Cheers!
The best I can think of...
[Serializable]
public class Record
{
public DateTime LastUpdated {get; set; }
public virtual bool ShouldSerializeLastUpdated() {return true;}
// other useful properties ...
}
public class EmployeeRecord : Record
{
public string EmployeeName {get; set; }
public override bool ShouldSerializeLastUpdated() {return false;}
// other useful properties ...
}
Basically, there are a few patterns that XmlSerializer respects; public bool ShouldSerialize*(), and public bool *Specified {get;set;} (note you should mark *Specified with [XmlIgnore] too...).
Not very elegant, I'll grant; but XmlSerializer only looks at public members, so you can't even hide them (short of [EditorBrowsable(EditorBrowsableState.Never), Browsable(false)]).
Related
I have data that is best described as "onion-like" in that each outer layer builds on the one below it. Below you will see a vastly simplified version (mine is several layers deeper but exhibits the same behavior at each level).
[CollectionDataContract]
public abstract class AbstractTestGroup : ObservableCollection<AbstractTest>
{
[DataMember]
public abstract string Name { get; set; }
}
[CollectionDataContract]
[KnownType(typeof(Test))]
public class TestGroup : AbstractTestGroup
{
public override string Name
{
get { return "TestGroupName"; }
set { }
}
[DataMember]
public string Why { get { return "Why"; } set { } }
}
[DataContract]
public abstract class AbstractTest
{
[DataMember]
public abstract string SayHello { get; set; }
}
[DataContract]
public class Test : AbstractTest
{
//Concrete class - members in this class get serialized
[DataMember]
public string Month { get { return "June"; } set { } }
public override string SayHello { get { return "HELLO"; } set { } }
}
I create an instance of TestGroup and add Test objects to it using the .Add that comes with the ObservableCollection.
When I serialize and de-serialize this structure I get the following
<TestGroup xmlns="http://schemas.datacontract.org/2004/07/WpfApplication2" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
<AbstractTest i:type="Test">
<SayHello>HELLO</SayHello>
<Month>June</Month>
</AbstractTest>
</TestGroup>
The output has left off the DataMembers in TestGroup. As I get deeper in my onion, no DataMembers that are higher are included (even from the abstract classes). I have tried adding [KnownType(typeof(TestGroup))] to both TestGroup and AbstractTestGroup without success.
The question: Why am I not able to serialize the DataMember Why in the TestGroup class?
Follow up question: Is there an alternative way to serialize and de-serialize a structure of this shape? I am planning on using the output locally to "load" the configuration the user specifies. I would prefer to not have to specify my own Serialization scheme if I can avoid it.
For those interested here is how I am generating the class, serializing, and de-serializing it.
TestGroup tg = new TestGroup();
tg.Add(new Test());
DataContractSerializer ser = new DataContractSerializer(typeof(TestGroup));
MemoryStream memoryStream = new MemoryStream();
ser.WriteObject(memoryStream, tg);
memoryStream.Seek(0, SeekOrigin.Begin);
string str;
using (StreamReader sr = new StreamReader(memoryStream))
str = sr.ReadToEnd();
Edit: For what it's worth I tried changing to using Serializable instead and have the same issue.
The reason why the property Why is not serialized is because TestGroup is a collection. And DataContract treats collections specially. The end result is that only the data in the collection is stored and none of the properties are stored.
Lists are stored in a way that any other list could read them in. The only differentiation is between collections and dictionaries. A good reference is http://msdn.microsoft.com/en-us/library/aa347850%28v=vs.110%29.aspx
UPDATE: I've seen some things online that may help you. In particular, change the abstract class attribute declarations to the following:
[DataContract]
[KnownTypes(typeof(Test))]
public abstract class AbstractTest { /* ... */ }
You could have a look at the documentation at MSDN on the KnownTypesAttribute. Apparently, there's also a constructor overload that takes a string that resolves to a method name that would be found via reflection and would be called by the DataContractSerializer to determine the known types for a base class (if you had multiple known types and/or possibly needed to dynamically return known types that may not be known at compile time). There's also web.config XML configurations for setting up known types.
UPDATE: I noticed that the KnownTypesAttribute attribute seems to be misused in the code examples in the OP. So, I wanted to elaborate the above with the full code that should work.
[CollectionDataContract]
[KnownTypes(typeof(TestGroup))] // Need to tell DCS that this class's metadata will be included with members from this abstract base class.
public abstract class AbstractTestGroup : ObservableCollection<AbstractTest>
{
[DataMember]
public abstract string Name { get; set; }
}
[CollectionDataContract]
//[KnownTypes(typeof(Test))] -- You don't need this here....
public class TestGroup : AbstractTestGroup
{
[DataMember] // Even though this is a derived class, you still need to tell DCS to serialize this overridden property when serializing this type
public override string Name
{
get { return "TestGroupName"; }
set { }
}
[DataMember]
public string Why { get { return "Why"; } set { } }
}
[DataContract]
[KnownTypes(typeof(Test))] // Again, you need to inform DCS
public abstract class AbstractTest
{
[DataMember]
public abstract string SayHello { get; set; }
}
[DataContract]
public class Test : AbstractTest
{
//Concrete class - members in this class get serialized
[DataMember]
public string Month { get { return "June"; } set { } }
[DataMember] // Even though this is a derived class, you still need to tell DCS to serialize this overridden property when serializing this type
public override string SayHello { get { return "HELLO"; } set { } }
}
See the comments next to the KnownTypesAttribute attributes in the example above.
UPDATE: Added the DataMemberAttribute attribute to the derived class' overridden properties.
UPDATE: OK, there may be an added dimension to this that is causing the behavior you're referencing. Do you have an interface or a class that is decorated with the ServiceContractAttribute attribute, where the service contains a method which returns one of these abstract types above? If so, then you also need to decorate said interface or class method that returns the abstract type with the ServiceKnownTypesAttribute attribute. A quick and dirty example follows:
[ServiceContract]
//[ServiceKnownTypes(typeof(TestGroup))] -- You could also place the attribute here...not sure what the difference is, though.
public interface ITestGroupService
{
[OperationContract]
[ServiceKnownTypes(typeof(TestGroup))]
AbstractTestGroup GetTestGroup();
}
HTH.
I'm setting up a WCF interface. My data contract looks like this:
[DataContract(Namespace = "wcf")]
[KnownType(typeof(TypeFromLibrary))]
public class MyClass
{
[DataMember]
public TypeFromLibrary myProp { get; set; }
}
Is it possible to use TypeFromLibrary in a DataContract like this? All of the examples I have seen only use int, string, double, etc as the property type.
NOTE: I have the copies of the library on both the server and client side of the WCF.
I just wanted to post what worked for me in case someone else was having trouble.
[DataContract(Namespace = "wcf", IsReference = true)]
public class NewType : TypeFromLibrary
{
public NewType(TypeFromLibrary baseObj)
{
//set all props here
}
public event EventHandler<SomeEventArgs> SomeEvent;
[OperationContract]
public string SomeBaseFunction()
{
}
[DataMember]
public CustomBaseProp SomeProp { get; set; }
[DataMember]
public int SomeInt { get; set;}
}
This worked as long as SomeProp was null. As soon as a value was given to SomeProp the same error showed up. I went to the next level and decorated CustomBaseProp as well and that worked. However, I stopped there because there are more custom classes in CustomBaseProp and wanted to seek alternative solutions. To fix completely fix it, you would have to decorate the CustomBaseProp class and other custom classes with the appropriate attributes.
I have two classes, RichString and RequiredRichString. In RequiredRichString, I'm re-implementing the Value property with the 'new' keyword. If I reflect the attributes on Value on RequiredRichString, I only get Required, but after testing posting markup multiple times, AllowHtml is still taking effect.
public class RichString
{
[AllowHtml]
public string Value { get; set; }
}
public class RequiredRichString : RichString
{
[Required]
new public string Value { get; set; }
}
In short: Why does ASP.NET still acknowledge the AllowHtml attribute when I re-implement the Value property with new?
If you have the flag set:
[AttributeUsage(Inherited=true)]
Then the attribute will be inherited.
But you can subclass the Attribute to your needs, ie MyAttribute(Enabled = true) in the base class and MyAttribute(Enabled = false) in the new implementation. For instance...
[AttributeUsage(Inherited=true, AllowMultiple=true, Inherited=true)]
public class MyAttribute : Attribute
{
public bool Enabled { get; set; }
public MyAttribute() { }
public void SomethingTheAttributeDoes()
{
if (this.Enabled) this._DoIt)();
}
}
public class MyObject
{
[MyAttribute(Enabled = true)]
public double SizeOfIndexFinger { get; set; }
}
public class ExtendedObject : MyObject
{
[MyAttribute(Enabled = false)]
public new double SizeOfIndexFinger { get; set; }
}
Note this answer: How to hide an inherited property in a class without modifying the inherited class (base class)? - it seems maybe you can achieve what you want by using method overriding rather than hiding.
I can understand why you would think otherwise for a new property, but my understanding is that new is about providing a new implementation, often in the form of a new storage mechanism (a new backing field for instance) rather than changing the visible interface of the subclass. Inherited=true is a promise that subclasses will inherit the Attribute. It makes sense or at least it could be argued that only a superseding Attribute should be able to break this promise.
The class that I need gets serialized as a web service response body.
The problem is, the properties from the base class get serialized along with it, and I can't have that for this service.
I need to block those properties from being serialized on only this subclass. So I tried hiding the properties using new but the base class properties are still being serialized (i.e. "Hello, world" is in the resulting http response body):
public class MyBaseClass
{
public string MyProperty { get { return "Hello, world"; } }
}
public class MyChildClass : MyBaseClass
{
[XmlIgnore]
[JsonIgnore]
public new string MyProperty { get; set; }
}
this gets returned via something like this:
return myHttpRequestMessage.CreateResponse(myStatusCode, myChildClassInstance);
So two questions
What up with that? Why isn't it honoring the child class with its decorations?
Is there another way to achieve what I'm trying to achieve (which is preventing the decorated properties from being serialized?
I know it's a total kludge, but until I have the time to fix the deeper issue (which is the operation that's forcing this inheritance), this is what I have to work with.
JSON
If you are using JSON.NET (which is a default JSON serializer in Web.API), then you will probably need to use custom ContractResolver. Answers for this question has a good examples of creating such type of class. In the following examples I will use IgnorableSerializerContractResolver from one of the answers.
Now you can register it in Global.asax:
var json = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
json.SerializerSettings.ContractResolver = new IgnorableSerializerContractResolver()
.Ignore<MyBaseClass>(x => x.MyProperty);
If you already using some contract resolver (for example CamelCasePropertyNamesContractResolver) then you will need to combine them somehow.
XML
I don't know what type (DataContractSerializer or XmlSerializer) of XML serialization are you using, but as I know, DataContractSerializer doesn't allow to exclude properties in runtime. You will need to use XmlSerializer. You can set custom serializers per type:
var xmlOver = new XmlAttributeOverrides();
var xmlAttr = new XmlAttributes { XmlIgnore = true };
xmlOver.Add(typeof(MyBaseClass), "MyProperty", xmlAttr);
var xml = GlobalConfiguration.Configuration.Formatters.XmlFormatter;
xml.SetSerializer<MyChildClass>(new XmlSerializer(typeof(MyChildClass), xmlOver));
Siple way
If you have access to your MyBaseClass and allowed to do some changes, then you can solve your problem using Data attributes:
[DataContract]
public class MyBaseClass
{
public string MyProperty { get; set; }
}
[DataContract]
public class MyChildClass : MyBaseClass
{
[DataMember]
public string MyProperty2 { get; set; }
}
In this case you can use default serializers (JSON.NET for JSON and DataContractSerializer for XML) and it will be solved for you automatically. Please note that you must add DataContract to MyBaseClass, or otherwise XML serialization will fail.
In order to ignore a property from the base class you could override this property in the derived class and decorate it with JsonIgnoreAttribute:
public class MyBaseClass
{
public virtual string MyProperty { get { return "Hello, world"; } }
}
public class MyChildClass : MyBaseClass
{
[JsonIgnore]
public override string MyProperty { get; }
}
You get an empty json object serializing it:
Debug.Assert(Newtonsoft.Json.JsonConvert.SerializeObject(new MyChildClass()) == "{}");
I want to specify that one property in an XML serializable class is an attribute of another property in the class, not of the class itself. Is this possible without creating additional classes?
For example, if I have the following C# class
class Alerts
{
[XmlElement("AlertOne")]
public int AlertOneParameter { get; set; }
public bool IsAlertOneEnabled { get; set; }
}
how can I specify that IsAlertOneEnabled is an attribute of AlertOne so that the XML serializes to the following?
<Alerts>
<AlertOne Enabled="True">99</AlertOne>
</Alerts>
If you are using XmlSerializer with default (non-IXmlSerializable) serialization, then indeed: this cannot be achieved without adding an extra class that is the AlertOne, with an attribute and a [XmlText] value.
If you implement IXmlSerializable it should be possible, but that is not a nice interface to implement robustly (the deserialization, in particular, is hard; if it is write-only then this should be fine). Personally I'd recommend mapping to a DTO model with the aforementioned extra class.
Other tools like LINQ-to-XML would make it pretty simple, of course, but work differently.
An example of a suitable DTO layout:
public class Alerts
{
[XmlElement("AlertOne")]
public Alert AlertOne { get; set; }
}
public class Alert
{
[XmlText]
public int Parameter { get; set; }
[XmlAttribute("Enabled")]
public bool Enabled { get; set; }
}
You could of course add a few [XmlIgnore] pass-thru members that talk to the inner instance.