I have a class with a read-only property defined. In my code I define this as a property with a getter only.
I want to be able to send this object back and forth across a web service. When I call a "Get" method in the service, it would be populated with a value on the service side. Once I define this property, I don't want the consumer of the web service to be able to set/change this property.
When I add a reference to this web service to a project, the object has the property serialized a few different ways depending on how I try to define the object on the service side:
internal setter: Creates the property in the WSDL. Visual Studio generates a class with both a getter & a setter for this property.
no setter: Does not create the property in the WSDL. Visual Studio then obviously does not define this property at all.
Read-only public member variable - Does not create the property in the WSDL. Again, Visual Studio will not do anything with this property since it doesn't know about it.
Allowing the consumer of the web service to set a value for this property will not cause any harm. If the value is set, it is ignored on the web service side. I'd just prefer if the consumer can't change/set the property to begin.
Is there any way to define a property as read-only? Right now we're using C#/.NET 2.0 for the web service, and (for now at least) we have control over all of the consumers of this service, so I can try changing configurations if needed, but I prefer to only change things on the web service and not the consumers.
I can be wrong, but I think the problem here is how serialization works - in order to deserialize an object the serializer creates an empty object and then sets all the properties on this object - thats why you need a setter for the properties to be included in serialization. The client code has the same "interface" to the object as the deserializer.
Caveat, I am a Java guy so the first part of my answer focuses on what may be possible in C#.
Firstly, with a custom serializer in Java, you can do almost anything you want, including directly setting values of a protected or private field using reflection so long as the security manager doesn't prevent this activity. I don't know if there are analogous components in C# for the security manager, field access, and custom serializers, but I would suspect that there are.
Secondly, I think there is a fundamental difference in how you are viewing Web services and the Web service interface as part of your application. You are right-click generating the Web service interface from existing code - known as "code first". There are many articles out there about why WSDL first is the preferred approach. This one summarizes things fairly well, but I would recommend reading others as well. While you are thinking in terms of a shared code library between the client side and server side of your Web service and maintaining object structure and accessibility, there is no such guarantee once you publish an API as a Web service and don't have control over all of the consumers. The WSDL and XSD serve as a generic description of your Web service API and your server and client can be implemented using different data binding configurations, object classes, or languages. You should think of your Web service interface and the XML that you pass in and out of it as describing the semantics of the exchange, but not necessarily the syntax of the data (your class structure) once it is internalized (deserialized) in your client or server.
Furthermore, it is advisable to decouple your transport related structures from your internal business logic structures lest you find yourself having to refactor both your server implementation, your Web service API, and your (and other's) client implementations all at the same time.
There's no built-in way to do this in .NET 2.0 as far as I know. In cases where I wanted to serialize a read-only property, I've implemented the IXmlSerializable interface so that I could control the ReadXml() and WriteXml() methods.
In later versions of the .NET framework, you can serialize read-only properties by setting an attribute on the backing field.
Related
I have been developing a WCF service for my project. I have multiple projects in my solution, explained below:
WCF Service - WCF Service Project
Business Logic - project contains domain logic
Data Access Layer - for accessing data
Core - project contains the business objects only (Many of them are sent as a response of service call - This contains the classes which are to be shared with client)
Log - project to log errors and activities
Service project puts call to Business project for the respective operation and the Business Logic project intializes the objects of the classes defined in Core object. And these objects are sent as the response of service call.
This is done successfully, i am able to share all public properties of the class defined in Core project. But i am unable to use DataContract/DataMember attributes in the core project as this is a non-WCF project. I need to achieve few tasks for which i have to use DataMember attributes like i dont want to share a property in case of null value, i don't want to share few properties of some objects with the client.
Please tell me if i am mistaken with the approach. And please help me achieving the above, i couldn't find any similar question on the forum.
Edit: (Let me try explaining it better)
All the projects are referenced in the WCF Service Project which consumes those project. This was to keep logical separation.
For Example, The Core project contains a class named User and this class is the return type of a service api. When this API is called, the logic initializes an object of User. And the object is returned as a result to that call.
In this case, i haven't used any [DataContract] attribute for the User class. And it works fine. Now i want to stop sharing few properties of this class, for this i needed to use [DataContract]/[DataMember] attributes, which are not being resolved in the Core project.
Ok, let me start by pointing out that data contracts and data members are not directly related to WCF. Actually, these attributes reside in a namespace that has nothing to do with services directly...theyre rather related to serialization and it's just a matter of adding a reference to the required assembly...i think it's System.Runtime.Serialization. I don't see why you can't add a reference to this assembly in your project.
The second question related to "hiding" members...i dont think you have to many options here. If you decorate a property with the DataMember attribute it will be serialized with the data contract, so there's no way you can't "hide" it. At best, what you can do is not to decorate a property with the DataMember attribute, but in this case the property will not be serialized, in other words, it will be ignored during the serialization process.
I'm writing a web service and have passed an object which is showing up as
<OfferDetail>
<OfferID>long</OfferID>
<InterestID>long</InterestID>
<RangeValue>string</RangeValue>
<Score>string</Score>
<Importance>string</Importance>
<Range>string</Range>
<ImportanceByOtherUser>string</ImportanceByOtherUser>
<RangeByOtherUser>string</RangeByOtherUser>
</OfferDetail>
in the web service placeholder but i don't want the
<ImportanceByOtherUser>string</ImportanceByOtherUser>
<RangeByOtherUser>string</RangeByOtherUser>
to be there is the place holders.
Note: i can't remove them from the object
If you're using WCF, then you probably have the DataContractAttribute applied to the object whose data you're returning via the service. If this is a service definition (which I doubt, but you didn't post any C# code), then you'll want to get rid of the OperationContractAttribute that's decorating these properties. But I believe it's the latter rather than the former—so I'd look for DataContractAttributes first.
HTH.
Just wondering why ?.
Are this members for internal web service usage, or private data? I've seen sometimes some developers publishing directly the ORM object through the web service. While it may works, It's often a bad idea as you don't want to expose the whole object, but only a subset of the object, or even a composition of several objects (customer's main detail + last orders in the month for example).
Thus I strongly advise you to refactor your code. You should create some DTO objects that are dedicated to data output of your web service, and command objects for input.
You specified you can't change the object, but what about adding another layer?
What type of webservice are you using? Depending on this you can use attributes like XmlIgnore, NonSerialized, IgnoreDataMember etc.
See
Question 1
Question 2
Its a known bug.
http://archive.msdn.microsoft.com/WsdlHelpGenerator/Release/ProjectReleases.aspx?ReleaseId=412
download the file and add the following in the web config
<webServices>
<wsdlHelpGenerator href="CustomWsdlHelpGenerator.aspx"/>
</webServices>
Href should point to the file downloaded in your the project
I'm trying to convert an ASP.Net web service to WCF application. The client is on the .Net Compact Framework which does not support WCF so I need to make sure the WCF keeps supporting ASP style webservices. When I add the web service reference in Visual Studio the generated proxy class' methods have extra arguments.
For example if a method is defined as:
public void GetEmpInfo(int empNo)
That method will appear in the proxy class as:
public void GetEmpInfo(int empNo, bool empNoSpecified)
What causes this, and how do I get it to stop?
Check out this blog post ...
Where did these extra boolean
“specified” members come from and what
do they do? The answer is the schema
that the WCF data contract serializer
generates by default. Because of the
way its versioning model works, the
serializer generates all data members
as optional elements. The older web
services stack, ASP.NET Web Services
(“ASMX”), uses a different serializer,
the XmlSerializer, which maintains
full schema and XML fidelity. The
XmlSerializer maps all optional
elements to two members: one
represents the data itself, and one
specifies whether or not the data is
actually present – this is the
“xxxSpecified” member. These
xxxSpecified members must be set to
true to enable the serialization of
the corresponding “actual data”
members.
The .NET Compact Framework does support a subset of WCF. You can review this support on MSDN. Take a look, it may support enough for you to remove your legacy Web Services support.
This happens for types with a default value of not null. In these cases, it's impossible for the web service to know whether a parameter was set to the default value or simply not set at all.
You can get rid of the extra specification parameter by decorating your operation with the [XmlSerializerFormat] attribute like:
[OperationContract]
[XmlSerializerFormat]
string GetEmpInfo(int? empNo);
This attribute can also be added at the Class level, and this would make sense in most cases.
I understand you can handle this situation using nullable types (int?), but I was unable to fix it using this.
Should I bind directly to objects returned from a webservice or should I have client-side objects that I bind to my gridcontrols? For instance if I have a service that returns object Car should I have a client side Car object that I populate with values from the webservice Car object?
What is considered best-practice?
In C# do I need to mark my classes as serializable or do something special to them?
This is a good question, which follows the sames lines as two questions I have asked myself:
Large, Complex Objects as a Web Service Result.
ASP.NET Web Service Results, Proxy Classes and Type Conversion.
Both of these may be a worthwhile read for you.
Heres my two bits:
Try to keep the return types of your Web Services to primitives where possible. This not only helps reduce the size of the messages, but also reduces complexity at the receiving end.
If you do need to return complex objects, return them as a raw xml string (I'll explain below).
What I then do is create a seperate class which represents the object and handles it's xml. I ensure the class can be instantiated from and serialized to xml easily. Then both projects (the web service and the client) can reference the DLL with the concrete object in, but there is none of the annoying coupling with the proxy class. This coupling causes issues if you have shared code.
For example (using your Car class):
Web Service (CarFactory) method BuyCar(string make, string model) is a factory method that returns a car.
You also write a Mechanic class that works on Car objects to repair them, this is developed without knowledge of the Web Service.
You then right a Garage class for your application. You add a web reference to the CarFactory service to get your cars, and then add some Mechanic's to your garage and then crack your knuckles and get ready to get some cars from the factory to get them working on.
Then it all falls over, when you get the result of CarFactory.BuyCar("Audi", "R8") and then tell your Mechanic.Inspect(myAudi) the compiler moans, because the Car is actually of type CarFactory.Car not the original Car type, yes?
So, using the method I suggested:
Create your Car class in its own DLL. Add methods to instantiate it and serialize it from/to XML respectively.
Create your CarFactory web service, add a reference to the DLL, build your cars as before, but instead of returning the object, return the XML.
Create your Garage adding a reference to the Mechanic, Car DLL and the CarFactory web service. Call your BuyCar method and now it returns a string, you then pass this string to the Car class, which re-builds its object model. The Mechanic's can happily work on these Car's too because everything is singing from the same hymn sheet (or DLL?) :)
One major benefit is that if the object changes in its design, all you need to do is update the DLL and the web service and client apps are completely decoupled from the process.
Note: Often it can be useful to then create a Facade layer two work with the web services and auto-generate objects from the XML results.
I hope that makes sense, if not, then please shout and I will clarify .
This really depends on what you are getting from the web service. If they are simple data transfer objects and you are only displaying data, then yes, you can bind. If you plan to edit the objects, it may not be usefull as you will need to track changes.
Do your objects and/or collections on the client track changes? If so you can use them.
If you have no change tracking, then you will need to track changes yourself, so you may need to translate the objects or wrap them in something to track changes.
Again, it really depends on what you are getting, what they support, what you are doing with them, as well as what response the server wants back for changes.
One thing you can do is to create client classes corresponding to the web service data contracts with any additional functionality that you want and set the web service reference to reuse existing types. Then there is no reason to create an additional wrapper class to bind to.
If you bind directly to the Web service types, you're introducing a coupling. Should the Web service change in future, this may have undesired side-effects that mean lots of code changes.
For example, what if you're using .asmx Web services today, then shift to WCF tomorrow? That might mean quite a few changes through your code if you've used types that WCF won't serialize.
It's often better in the long run to create specific client-side objects and then translate to and from Web service data contract types. It may seem a lot of work, but this is often repaid greatly when it's time to refactor, as your changes are localised in one place.
If you are the owner of both the web service and the client.
And you need the parameters of the web service calls to be complex classes which contain not only data but also behavior (actual coded logic) then you are in a bit of a pickle when developing these web services using web service frame works.
As suggested in the answer by Rob Cooper you can use pure xml as web service parameters and xml serialization, but there is a cleaner solution.
If you are using Visual Studio 2005 (probably applies the same for 2008), You can customize the way VS creates you proxy as described in this article:
Customizing generated Web Service proxies in Visual Studio 2005
This way you can tell VS to use your own classes instead of generating a proxy class.
Well when I think of it, it's pretty much same solution as proposed by Rob Cooper, with the little twist, that you wont be writing a Facade layer your self but will be using VS itself as this layer.
I'm still new to the ASP.NET world, so I could be way off base here, but so far this is to the best of my (limited) knowledge!
Let's say I have a standard business object "Contact" in the Business namespace. I write a Web Service to retrieve a Contact's info from a database and return it. I then write a client application to request said details.
Now, I also then create a utility method that takes a "Contact" and does some magic with it, like Utils.BuyContactNewHat() say. Which of course takes the Contact of type Business.Contact.
I then go back to my client application and want to utilise the BuyContactNewHat method, so I add a reference to my Utils namespace and there it is. However, a problem arises with:
Contact c = MyWebService.GetContact("Rob);
Utils.BuyContactNewHat(c); // << Error Here
Since the return type of GetContact is of MyWebService.Contact and not Business.Contact as expected. I understand why this is because when accessing a web service, you are actually programming against the proxy class generated by the WSDL.
So, is there an "easier" way to deal with this type of mismatch? I was considering perhaps trying to create a generic converter class that uses reflection to ensure two objects have the same structure than simply transferring the values across from one to the other.
You are on the right track. To get the data from the proxy object back into one of your own objects, you have to do left-hand-right-hand code. i.e. copy property values. I'll bet you that there is already a generic method out there that uses reflection.
Some people will use something other than a web service (.net remoting) if they just want to get a business object across the wire. Or they'll use binary serialization. I'm guessing you are using the web service for a reason, so you'll have to do property copying.
You don't actually have to use the generated class that the WSDL gives you. If you take a look at the code that it generates, it's just making calls into some .NET framework classes to submit SOAP requests. In the past I have copied that code into a normal .cs file and edited it. Although I haven't tried this specifically, I see no reason why you couldn't drop the proxy class definition and use the original class to receive the results of the SOAP call. It must already be doing reflection under the hood, it seems a shame to do it twice.
I would recommend that you look at writing a Schema Importer Extension, which you can use to control proxy code generation. This approach can be used to (gracefully) resolve your problem without kludges (such as copying around objects from one namespace to another, or modifying the proxy generated reference.cs class only to have it replaced the next time you update the web reference).
Here's a (very) good tutorial on the subject:
http://www.microsoft.com/belux/msdn/nl/community/columns/jdruyts/wsproxy.mspx