How can I use an interface (from which classes implement) in an XML web service?
When I do so, I get a YSOD claiming the interface is not serializable. If I add the Serializable attribute to the interface's class, there's another error which hampers progress (can't remember which).
For the most part interfaces are not serializable without some work. Usually this error is encountered when the class being serialized contains an object that is using an interface as a variable, or some variation of this. For instance, a property like this would throw an error:
[Serializable]
public class TestClass
{
private ICustomInterface _iCustomInterfaceObject;
public ICustomInterface CustomInterfaceProperty
{
get { return _iCustomInterfaceObject; }
set { _iCustomInterfaceObject = value; }
}
}
For the sake of the argument (and not making me type additional validation code), let's say that you always are assigning CustomInterfaceProperty to an object that inherits from ICustomInterface (as is required when using interface types like this). Even if it is 100% sure to always be populated, it won't allow you to serialize the TestClass.
To get around this, you need to make sure the interface you are using, the one that is throwing the error, also inherits from ISerializable. That way you are promising that all of the objects inheriting from ICustomInterface also have serialization methods implemented.
Unfortunately, this is not the case when using xml serialization. If you are using the serializers found in System.Xml.Serialization then this method won't work, since, as Robert Harvey pointed out, an interface does not contain a parameterless constructor (which is required when using the xml serializers). My suggestion for now, if you are set on this method of serialization, attach the attribute [XmlIgnore] to the section in question and move on from there.
My advice is to treat the objects that go over the wire as basic data transfer objects and nothing more. You're tempted to just use your domain objects and serialize them, but as you're already seeing, normal in-memory objects can have far more complexity than can be serialized without a lot of work, and sometimes not at all.
You can also end up limiting functionality of your domain classes just to keep them serializable.
Finally, a more subtle bug to avoid, and a reason to have separate DTO's, is that you otherwise are tightly coupling your domain objects to a publicly published interface i.e. the web service itself. Versioning a web service can be a hassle, and it's easier if your service interface isn't tightly coupled to your domain classes.
I'm guessing that the other message is that you can't serialize the interface because it doesn't contain a default (parameterless) constructor.
If the underlying classes are framework classes, you might be hosed. Some of them are not marked serializable, and some of them do not have parameterless constructors.
Also, you may be getting confused between runtime serialization and XML serialization. XML Serialization is what the old ASMX web services use. It does not pay much attention to the [Serializable] attribute, but mostly just serializes the public read/write properties of public classes which have a default constructor.
Related
I'm trying to find out if there's a way to stop functions/methods from being added (EDIT: by other developers) to a class for the case where the object is a Model or DTO which should not contain methods (to prevent 'abuse' of the Models/DTOs by others, who may try and add 'helper' methods etc).
Is there any way to achieve this?
Use reflection and write a unit test that fails if a model-class has methods.
Mark all you model classes with a custom attribute. Then make a unit test that uses reflection to load a given assembly, iterate all classes in that assembly and check that classes marked with the model attribute does not have methods. This should be fairly straight forward using reflection.
I believe you are trying to solve a procedural issue with code where you should be using communication.
Your colleagues (i assume) are operating on the code files with 'full trust' privileges. If they break that privilege you should open a dialogue. Use the change as an opportunity to educate them on the intended design. Perhaps they are correct and you will be educated!
I suggest simply making the intended design obvious in the class name and with a comment stating the intended nature. Perhaps quote the design document(s) that informed the class.
You cannot hinder anyone with full write-access to your code-base to do so. The only two things you may do to avoid it are create some CodeAnalysis-rule for FXCop as mentioned by Christian.K in the comments or by writing your DTO-class so that it is undoubtly a DTO that should not have any methods by using a unambigious name for the class and if this is not enough provide some code-comments that notifies the coder to do not so.
However you may need some kind of method if using collections e.g. where you will need some kind of comparision if two instances of your DTO are equal, so you have to provide at least an Equals- and GetHashCode-method.
You don't need to use a struct to prevent additions to a class. You can use the sealed keyword
public sealed class MyDTOObject { ... }
Now, you can not inherent a class and also prevent inheritance (which is essentially what you're asking). The very fact of inheriting MyDTOObject is creating a new class which is based off of not equal to, or restricted, or defined in any way by the implementation of MyDTOObject.
You can use an abstract class, to force derived classes to implement certain methods, but not the other way around.
If you want to prevent others from deriving from your class and implementing helper methods, you must use the sealed keyword, or mark the class internal.
You may prevent the class being extended or inherited by marking it final that way nobody would be able to extend your class and hence not being able to add any behavior. But stop and ask yourself whether you want to do that or not, because then you'd be signing an invisible contract that everything ever required by the class is written in the class and this class needs no further addition.
To be clear, I was talking in Java context.
I have a class say supplierAddress which comes from a webservice (it is a datacontact). I then have a second class myAddress which inherits from that class and has a few more constructors and metods.
What I want to do is pass a myAddress back to the webservice. When I pass a cast down myAddress it throws seriazation errors, which makes sence as its a refrence object and the whole object is still being passed even if im casting down.
Is it possible to clone just the base class of an object? Is what im trying to do possible/correct ?
You should specify Known types for your base class.
UPDATE: additional clarification.
SOA (Service-Oriented Architecture) paradigm doesn't support such common features like polymorphism or method overloading. This behaviour based on very simple fact: you don't know which platform will consume your service. Its definitely possible to consume your service in platform or language that doesn't support such thing like inheritance or method overloading.
That's why you should create your service functions with unique names and that's why you should explicitly stated what types you're going to pass instead of base class reference.
When you specify known types this information would expose out of your service through metadata and every client could understand how to deal with your responses.
I have 3-rd party dll. From that I receive an object of some type (I know its interface, but not all the object). That object is not marked as serializable and I'm not related to that libruary development at all.
I want to serialize it to some storage and then receive it from storage with the same state later (public/private, references etc.). I got here one option - make my own serialization mechanism that will act the same as .NET serializers with the only difference - it won't revise serialization attributes.
Is that the best way?
Thanks.
You can use XmlSerializer or DataContractSerializer to serialize types not marked with SerializableAttribute.
There may be other options. And can always go ahead with custom implementation if nothing works for you.
You can make your own class inheriting from that object and serialize it.
OR you can make your own replica of that class and make some explicit (or implicit, but not recommended) conversion methods.
I've seen many different ways to serialize objects in C# that I'm not sure which one to use and when.
In the current situation I'm serializing for exposure through WCF so I'm guessing the [DataContract] attribute is the way to go.
Currently I'm reading in some XML, then exposing the resulting object through WCF. So I am deserializing XML for which I have no access to the original classes (therefore I'm rebuilding the class and can implement serialization whichever way I want). Then it has to be serializable for the WCF.
But if [DataContract] is good for this case, then why wouldn't I use it all the time instead of ISerializable, or the [Serializable] attribute?
So a bit of two questions in one, which to use for this problem, and why are there different ways to serialize.
DataContract is a good place to start for basic serializing. But if you want to control exactly how the object is serialized use the ISerializable interface. Also, the data contract attribute does not get inherited, but the ISerializable will
ISerializable has been around since .net 1.1. DataContract was introduced in .net 3.0 to simplify serializing for most cases.
Using ISerializable, by implementing GetObjectData, you can customize the way an object is serialized/deserialized within the object's class without having to create a serializer
If you create a WCF service, I think you should stick to DataContract. One of its big advantages is the opt in (i.e. no bad surprises) mechanism.
I'd like to override the Serialize methods of the ASP.NET JavaScriptSerializer class. Nothing too fancy, I just want to do some additional post processing to the serialized string returned from .NET.
Unfortunately, none of the methods on this class are declared virtual and the class itself does not derive from an interface or abstract class (seems like a strange oversight given how many of the core .NET Framework classes are designed for extensibility).
Based on some reading I've done on the subject, it appears that I have a couple of options to choose from.
Create an extension method. I'm not a huge fan of this option, since it involves creating a new method (compiler won't allow using the same name/signature twice) that class consumers would need to be aware of.
Derive a new class from JavaScriptSerializer that has the exact same signature. Since JavaScriptSerializer has no virtual methods, I would use the "new" keyword in each method/property declaration in order to perform method hiding. I think this option is considered a decorator pattern?
Create a new interface called IJavaScriptSerializer that would have the same signature as JavaScriptSerializer. Remove all references in my code to JavaScriptSerializer and replace with references to the newly created interface.
I'd love to hear about additional approaches and the pros/cons of each approach.
Thanks for taking the time to read.
You're misunderstanding the Decorator Pattern, which refers to an object that inherits a class and wraps another instance of that class. (This is very common for streams). In your case, it's inapplicable.
I would recommend that you make your own replacement (or wrapper, whichever you need) for the JavaScriptSerializer class, without trying to have an identical API. If you need to be able to swap implementations, I would make an interface or base class with the core methods, and have two concrete implementations of it, one wrapping the original and one adding your post-processing.
In general, when designing classes, you should design to meet your needs, not to copy the .Net Framework's built-in classes.
Go to http://json.org and d/l one of the several classes that have source code, for JSON serialization.
Then, put in your post-processing, compile and use in your project.
Ideally, at this point I would create an extension method so I can just do this:
List<MyObject> s = fillObject();
return s.ToJSON();