My understanding is that all contract-implementing code has to be in a single class, that can become very large, obviously. How do I avoid this? I really prefer to have a few small classes doing one part of the communication with clients than a single behemoth class.
The only idea I could think of is using multiple interfaces implemented by a single class split up by partial, but I don't think this is really solving the issue.
You might want to use Inheritance, depending on the structure of yoru code. Usually you can break all code up into smaller pieces, helpers, sub-routines, etc.
It's like with any other API-development, you don't want / don't need everything in the same place in the same package.
First, if your contract is big, can they be refactor into more specific service contracts?
The contract implementation class can be implemented as entry point method. You can always model the implementation and define the appropriate abstraction and have your service contract implementation class calls those internal implementation.
If you could change your code fundamentally, you could expose just a single endpoint that works with request/response messages. This way there could be a single end-point and a single service definition that takes a (possibly derived) request message and returns a response message. Your interface into the service would then just be a single method and in the server side implementation you would route that request object to the actual service implementation (possibly determined by a factory) possibly using metadata on the request message (or even it' type-name) to define what service is being called.
So, your end service interface would just have a method like this:
public interface IServiceRequestor
{
Response ProcessRequest(Request request);
}
This allows you to handle a possibly unlimited number of exposed services without having to know what they will be at compile/dev time, and also avoid a proliferation of Service methods defining the service calls available
That 'single class' usually is a facade, just a communication front-end.
So you should not implement all your logic in the Service implementor.
And your interfaces should be as small as possible (do 1 thing well). But if necessary your facade can call on multiple classes.
We have about 60 partial files called "BeamServer.cs", each in a sub-folder that corresponds to the purpose of the functions in that file. Any helper classes (or other helper files) that are for the same area of our program resides in that folder as well.
Your "one class" represents your "one business need". We found a nice side benefit in that if one of the members of our team is working on the "Accounting" portion of BEAM (our software), then they would check out the file "Accounting\BeamServer.cs" and none of the rest of the team would be effected.
EDIT: Also, the class should only contain the method signatures (and wrapper functions that simply call base.Channel.DoSomething()... Any data structures would of course be their own class files (such as "Person.cs" or "Employee.cs" or whatever).
Related
So I have a layered application that I am adding a WCF service interface on top of. The service is simply a facade with all of our business logic already existing in Business Objects (BOs) within the Business Logic Layer (BLL) which is a class library. Within the BLL we use constructor injection to inject dependencies into the BOs. This is all working with good unit testing, etc. On to the problem...
Ordinarily I'd simply create a set of Request/Response objects as DataContracts for each service method with the appropriate properties for the operation. If the operation required one of our "entities" to be passed either to or from the method, I'd simply define a property of that type and everything would be fine (all of our BOs are serializable). However when one of these "entities" is passed into a service method, WCF deserializes the object without ever invoking the constructors we've defined and, as a result, the dependencies don't resolve.
Let's use the case of a service method called CreateSomething. I'd normally define this as a service operation with a signature like:
CreateSomethingResponse CreateSomething(CreateSomethingRequest request);
CreateSomethingRequest would be a DataContract and have amongst its properties a property of type Something that represented the "entity" being passed into the service. Something, in this case, is a business object that expects to receive an instance of the ISomethingRepository interface from the DI container when instantiated - which, as I said above, does not happen when WCF deserializes the object on the server.
Option #2 is to remove the Something property from the DataContract and define each of the properties explicitly in my DataContract then inside my service method, create a new instance of the Something class, letting the container inject the dependency, then map the property values from the DataContract object into the BO. And I can certainly do that but I am concerned about now having two places to make changes if, say, I want to add a property to the Something type. And, with a lot of properties, there's a lot of code duplication.
Has anyone crossed this bridge and, if so, can you share your thoughts and how you have or would approach this situation in your own applications? Thx!!!
There are two answers on your problem:
First: Do not send your entities and use data transfer objects instead. Your entities are business objects with its logic and data. The logic of business objects is most probably used to control the data. So let the business object control its data in business layer and exchange only dummy crates.
Second: If you don't want to follow the first approach, check documentation of your IoC container. There are ususally two methods for resolving dependencies. For example Unity offers:
Resolve - builds new instance and injects all dependencies (necessary for constructor injection)
BuildUp - takes existing instance and resolves all property dependencies. This should be your choice.
Thanks, Ladislav, for your answer as you confirmed what was already in my head.
What I ended up doing was to change my approach a little. I realized that my use of a business object, per se, was overkill and unnecessary. Or perhaps, just misdirected. When evaluating my requirements, I realized that I could "simplify" my approach and make everything work. By taking each logical layer in my application and looking at what data needed to pass between the layers, I found a design that works.
First, for my business logic layer, instead of a business object, I implemented a Unit of Work object: SomethingManager. SomethingManager is tied to my root Something entity so that any action I want to perform on or with Something is done through the SomethingManager. This includes methods like GetById, GetAll, Save and Delete.
The SomethingManager class accepts two objects in its constructor: an IValidator<Something> and an ISomethingRepository. These will be injected in by the IoC container. The former lets me perform all of the necessary validation using whatever framework we chose (initially the Validation Application Block) and the latter gives me persistance ignorance and abstracts the use of Linq-to-SQL today and makes upgrading to EF4 much easier later on.
For my service layer, I've wired the IoC container (Unity in this case) into WCF so the service instance is created by the container. This allows me to inject an instance of ISomethingManager into my service. Using the interface, I can break the dependency and easily unit test the service class. Plus, because the container is injecting the ISomethingManager instance, it is constructing it and will automatically resolve it's dependencies.
I then created DataContracts to represent how the data should appear when transferred across the wire via the service. Each Request/Response object contains these DataContracts as DataMembers rather than referencing my entity classes (or BOs) directly. It is up to the service method to map the data coming from or going to the Business Logic Layer (via ISomethingManager) - using AutoMapper to make this clean and efficient.
Back in the data layer, I've simply extended the generated entity classes by defining a partial class that implements the desired interface from the BLL. For instance, the Something L2S entity has a partial defined that implements ISomething. And ISomething is what the SomethingManager (and ISomethingManager interface) and ISomethingRepository work with making it very easy to query the database and pass the L2S entity up the chain for the service layer to consume and pass on (without the service layer having any knowledge or dependency on the L2S implementation).
I appreciate any comment, questions, criticisms or suggestions anyone has on this approach.
Just personal style, I guess, but I hate having 2 files for my WCF Services. I tend to like to copy/paste the interface into the .cs file so that I only have to deal with a single file.
Any dangers in doing this?
Not dangers per se - but there are times when it is very useful to have a separate assembly with your service, operation and data contracts (just the contracts, the interfaces, basically) - when you need to share those between the server and the client side.
There's really no point in sharing the whole service implementation code (the actual service class, that implements the service interface), with the client.
Plus: if you have your interfaces in a separate file (and possibly assembly), it makes it easier to write unit tests, especially if you want to mock a service. Gets a bit messy if you mix interface and class into a single file.
So I consider it a useful and helpful best practice to have separate files for interfaces and implementations (actually: always one class per file only), and to put all service- and data contracts (and fault contracts) into a separate assembly.
Actually, I like to go beyond two files, and have two separate projects. One project holds the interface definition. The primary value is for integration testing. I like to make a third project with a WCF client. That client accesses the interface in the "shared" assembly.
Remember the mantra of Testivus: "When writing the (production) code, think of the test; When writing the test, think of the code."
why is it recommended to define service contract as an interface.
Any specific advantages over having them as classes?
The primary goal is separate definition of your service from implementation
The user of your service should not know anything about how you implemented your service, but he should know what operations he can do and how.
That's why its using an interface instead of class, because interface doesn't contain an implementation.
You can share your interface one time and then never worry for years even if you changing implementation of its methods every day. End users will not need to recompile the code that's using your service
Of course [there are several advantages] !
The main one is probably the ability to implement multiple classes which support said Interface and to use these classes interchangeably [with regards to the particular interface]. One of the direct uses of this is with Mock classes used for testing; This is also used with IoC (Inversion of Control) pattern, and more generally wherever we care about the "What" rather than the "Who", i.e. What matters is that whichever class is in place it behaves as per the contract (the API) regardless of "who" (which class) it is.
Another salient advantage of Interfaces is the ability to modularize behavior. For example your application may implement a concept which works, say, like a List (can be iterated over, supplies a number of items, etc.) and like a widget validator (some application specific thing). By having two interfaces "describing" this particular object, you can use instances of that class wherevever you'd use a List (and just that) and similarly you can use it as a widget validator (and just that) whereever these validator are needed. This is akin to multiple inheritance but more flexible.
In a nutshell (and some other answers started with this), the Interface defines the contract and the Class(es) implement(s) it.
Technically, a single class could do both of these things, i.e. you do not __need __ to have Interfaces, but it is very preferable to define APIs for most any behavior which may be implemented by several classes (whether multiple implementations of almost the same thing as with "mock classes", or very different classes but supplying one particular generic service/feature as say two very distinct Lists.)
Because an interface IS a contract and a class is the means to fulfill a contract. There can be many different ways to fulfill a contract based on the context, so It makes more sense to have the contracts as interfaces. which can have different implementations
WCF promotes good design by using interfaces and contracts etc. What baffles me is that, for example in my case if I have 2 sets of business functionality like ICustomerMgmtBIZ
and IProductMgmtBiz. If these two are ServiceContracts, and I have an interface like
IBusinessService:IProductMgmtBIZ,ICustomerMgmtBIZ
and implementation class BusinessService. I see that BusinessService class will be having too much implementation. The workaround I have been using so far is by implementing partial classes.
So bluntly put, can a WCF service have only 1 implementation and 1 service contract ??
No, it is possible to implement more than one Service contract on a WCF Service type (the class that is attributed with the ServiceBehavior attribute), since it is just a matter of having the class implement multiple interfaces. If you are using any of the Visual Studio templates or other kinds of code generators, this may not be immediately clear. However, although you can implement more than one Service Contract interface on a Service type, it does not do you much good if you need the service, presumably a singleton in this case(?), to behave as one service. IBusinessService implies that you need all of the service's functionality to be callable from one client proxy, so that all operations may operate in the same logical session (similar to ASPX web session). If that is not the case, then you are free to define individual proxies for each contract interface, but that will also require that you support one endpoint for each contract.
Is it an absolute requirement that you can only have on WCF ServiceHost instance for your implementation? What factors are influencing your decision?
By the way, partial classes do not trouble me anymore. The idea of splitting out code into multiple files now seems rather natural. For example, storing partial classes in files like ServiceType_IProductMgmtBiz.cs and ServiceType_ICustomerMgmtBIZ.cs seems natural enough, in addition to storing the core logic in ServiceType.cs.
Finally, the following question might be of use...
WCF and Interface Inheritance - Is this a terrible thing to do?
Bluntly put, no - sort of - yes, but. Any workaround is non-optimal and involves using an "IBlank" as a master WCF interface (where your interfaces derive from IBlank), and two endpoints, one implementing IProductMgmtBIZ and the other implementing ICustomerMgmtBIZ. I don't have my dev machine in front of me, this might involve some other overrides. So, at the WCF level you're screwed unless you want to have two WCF ServiceHosts (which is perfectly reasonable).
In short, the workaround is inelegant. Its easier to have two WCF endpoints on the same port with a different extension.
I am developing a WCF web service which has become quite bloated. What techniques do you use to split up the implementation of the contract?
Well you have a couple choices:
First, you could leave it all in one class, but split up into different files using the partial class feature of C#.
Second, you could have the main service class just pass requests off to one of a number of other actual classes that are organized logically.
A third alternative is to consider refactoring to reduce the number of operations you have. Is there actually a use to all of the methods you're exposing?
Finally, you could always split up the service into multiple WCF services.
It's hard to answer your question if you don't give any more information.
Do you mean that your service interface is bloated, or the class implementation? It's hard to answer well, if I don't see the code, or have no other information, anyway, I'll try:
Notice that WCF service is basically just a regular class that implements an interface and has some attributes on its methods. So all the other good OO design rules apply to it. Think about what it does, does it have really single responsibility, if not try to outsource some of that responsibility to other classes that your service depends on. If you need a non-default constructor, use IInstanceProvider to create the service class, and supply it with its dependencies (or if you use Windsor Container use WCF Facility).
If you really want to you can streach your inheritance chain, and move some of the code to a base class. I don't do it, however and always prefer to use composition over inheritance.
Inspect your service contract, and think about how cohesive it really is. Maybe what you should do is to split it, into few smaller, more cohesive services.