I have looked on the web but I am confused as to whether a wrapper service wraps a legacy application, or a set of complex services.
Update:
Judging by the answers I have received there is no accepted definition for a "wrapper service" in SOA, and after further investigation I realised that "wrapper services" depends on who defines it. I mean in an Oracle context.
All - part of the confusion around this term stems from simply being mis-spoken...
It's NOT "wrapper SERVICE", but rather "service WRAPPER"
:-)
Once you get the TERM itself correct, things start to make sense:
- a "wrapper SERVICE" sounds like a SERVICE which creates "wrappers" - WRONG;
- a "service WRAPPER" sounds like code which encapsulates or "wraps" an existing body of code, and gives it the ability to act as a SERVICE - RIGHT !
It's now obvious we're talking about SERVICE WRAPPERS here, and now it starts to become clear(er) that it DOESN'T EVEN MATTER what sort of code is encapsulated "inside" the wrapper, because the wrapper code acts like a FUNCTION, where there is a "interface" (established input formats & output formats) that is all the users interact with, making the guts inside a "black box" the user NEVER needs to know about...
This wrapper then presents to the user as something like a FUNCTION; the user submits inputs to the "service"... and gets back outputs. The wrapper itself then has code which internally interacts with the legacy or new code inside the wrapper, formulates an output, and returns this output to the requester (user) :-) ...
Historically service wrappers were the favorite way to re-purpose legacy code which did NOT all by itself behave like services (background-running programs capable of listening & responding to requests, aka daemon processes), but as organizations worked to evolved toward SOA, this was a great way to quickly turn legacy "apps" - typically NOT running in background - into services.
Hope this helps.
-MV markvogt.vogtland.ws
Arguably the entire point about SOA is that everything is a wrapper. That is , a web service is just a facade, and there is no way to tell whether it fronts a "legacy application" or "a set of complex services".
I understand a wrapper service as a service that wraps something, be it another service, a set of services, or a legacy application.
"wrapper service" which is also more widely known as "legacy wrapper" is used to wrap a legacy component to prevent coupling issues in soa.
hiding complex systems or a set of services is done using the "facade service"
Wrapper services is group of one or more than one web service which encapsulate the logic of different module, due to which an individual module is able to communicate with other module with minimum integration concerns.
Related
I have a small app (Win Forms) where I have two different repositories (SQL Server and Redis) both implementing a interface IFilterRepo.
I also have a service class that depends on the IFilterRepo. The client (the Win Form) call the service to access filter data.
I want the client to have two radio buttons where a user can choose which repo to use. And here comes my dilemma. How should I tell the service which concrete class to instantiate as IFilterRepo? I mean, ALL Unity registrations and references to it shall be done in the composition root. Is that "rule" really possible in this case?
This is a common question, and the answer is generally to use an Abstract Factory.
Here is a good article on the subject (I link this all the time, but I didn't write it):
http://blog.ploeh.dk/2012/03/15/ImplementinganAbstractFactory/
As noted in the article, you can make the factory part of the composition root, so that calling container.Resolve() inside the factory doesn't violate that rule.
Edit
You would register different implementations of the service using a name (string):
http://msdn.microsoft.com/en-us/library/ff648211.aspx
myContainer.RegisterType<IMyService, CustomerService>("Customers");
And then your factory would resolve by that name:
public IFilterRepo Create(string myName)
{
return myContainer.Resolve<IFilterRepo>(myName);
}
Edit 2
The question you asked in your last comment is a bit much to answer here, but in brief: your factory itself would implement an interface, and would be resolved and registered via the container.
As a general matter, I would not recommend accessing a repository directly from the code behind--I would at least look at having a layered architecture (or better, an Onion architecture, which works very well with DI).
Finally, I have not done WinForms development in years, but I don't think it fits perfectly with using a container/Composition Root, since you don't have full control over the lifecycle of your objects (you can't inject services into your form constructors). The same is true of ASP.Net Webforms. So you may have to use property injection for your factory and other services needed in your form, or just resolve the factory directly via calling a static instance of the container (container.Resolve()). This is imperfect, and goes against the idea of having a Composition Root, and more toward service location.
You might google keywords "Unity WinForms" and/or "[OtherDIFramework] Winforms" to get some ideas of how to structure your code.
I'm rearchitecting a large web forms ASP.Net application, inserting a service layer to take away unwanted responsibility from the presentation layer.
I've seen a lot of examples where all the service methods are contained in one class.
Is this common / best practice? Or is it perfectly feasible to have a number of service classes within the service layer? I'm leaning towards having more than one service and those services being able to talk to each other.
Any guidance, pros/cons?
Richard
P.s. Note that I'm not talking about a web service layer, WCF or otherwsie, although that might become more relevant at a later date.
The SOLID principles, specifically the Single Responsibility Principle would suggest that having all of your functionality in one object is a bad idea, and i tend to agree. As your application grows the single class will become difficult to maintain.
Your comments to Yuriys answer would suggest you want to use an IOC container. Lets consider that in more detail for a moment...
The more functionality this single class contains, the more dependencies it will require. You could well end up having a constructor on the service that has a long list of parameters, simply because the class covers a lot of ground and depends on other functionality at a lower level, such as logging, database communication, authentication etc. Lets say a consumer of that service wants to call one, and only one specific method on that class before destroying the instance. Your IOC container will need to inject every dependency that the service could 'possibly' need at runtime, even though the consumer will only use maybe 1 or 2 of those dependencies.
Also from an operational perspective - if you have more than one developer on the team working on the service layer at the same time, there is more possibility of merge conflicts if you are both editing one file. But, as suggested you could use partials to counter that issue.
Usually a dose of practicality alongside a well known pattern or principle is the best way forward.
I would suggest researching Service Orientated Architecture if you havent already, as it may help you answer some key decisions in the approach to your solution.
Of course, it can.
Moreover, I believe that would be better to extract from this God service layer class few interfaces by functionality (i.e. ISecurityService, INotificationService etc.) and implement each interface in separate project. Also, you can utilize some IOC container to resolve class that implement service's interface. This way you can change each service's implementation independently without changing client functionality.
At least, for the first time you can mark your service super class as partial, then split it up by functionality into few .cs(.vb) files with meaningful names and group them together in Visual Studio. This will simplify navigating across service methods.
My take on structuring an application would be to start with splitting the application into two projects AppX.Web (UI logic) and AppX.Business (business logic), but still keep them in the same VS solution. The clarify in structure between business logic and UI logic helps you understand what services are shared among multiple web pages and which are local to a singel web page. You should avoid reusing code directly between the web pages, if you find that this is necessary then you should probaly move that piece of shared code to the business logic layer.
When implementing the business logic project you should try to create separate classes for different type of business logic. These classes can of course talk to eachother, but do avoid having the web pages talk to eachother.
Once you have separated UI logic from business logic you can continue to break down the AppX.Business code into smaller pieces if necessary. Common examples include:
AppX.Data: A Data Access Layer (DAL) which isolate all data manipulation from the actual business logic
AppX.Dto: Data Transfer Objects (DTO) which can be useful in many scenarios, e.g. when sending data to the client browser for processing by jQuery
AppX.Common: Shared logic which is generic to many other applications, this can be helper classes you have previously created or things which should be reviewed after the project for inclusion in company wide support classes.
Finally, let's talk about going all-in and expose your business logic as a WCF service. In that case you actually need not change anything in the existing structure. You can either add the WCF service to your existing AppX.Web project or expose them separately in AppX.Service. If you have properly separated business logic from UI logic the WCF layer can be just a thin wrapper around the business logic.
When implementing the WCF service it is quite possible to do all of that in a single class. No real business logic is available in the WCF service as it just make direct calls to the business logic.
If you build a new application you should consider you overall design up front, but now that you are rearchitecting I think you should work step-by-step:
Start by creating the AppX.Web and AppX.Business Projects
Identify services and create classes in AppX.Business for those services
Move code from the AppX.Web project into the new classes in AppX.Business, and make sure you call them from the web project.
Continue with additional break-down if you feel you need to do so!
I'm currently working with web services that return objects such as a list of files e.g. File array.
I wanted to know whether its best practice to bind this type of object directly to my front end code for example a repeater/listview or whether to first parse it into my own list of "file class" e.g. customFiles[]
If the web service changes then it will break my front end code, however if I create my own CustomFile class, then i would only need to change my code in one place to fix the issue, but it just seems like a lot of extra work to create the same classes from a web service, i wanted to know what is the best practice for this type of work.
There is a delicate balancing act in properly encapsulating implementation details. Too little encapsulation is a maintenance nightmare as small changes in any area break the application. Too many layers is a different kind of maintenance headache altogether.
In this particular case I would create a small layer in your application to encapsulate the web service calls. This will ease your maintenance in both the application and the service as they will be loosely coupled.
It sounds like you have already answered your own problem. Best practice is to create your own custom class for the reasons you point out, but it is significant extra work.
If the webservice isn't likely to change then just use the existing classes, but if you need to cater for change then create your own.
Returning a class is fine as long as your client knows how to deserialize it. If it's truly a web service, where you don't have control over both ends of the conversation, it's more common to start with schemas for XML request and response streams. That decouples the client from the web service a bit more and allows any client that can send XML via HTTP and consume an XML response fair game.
In an effort to understand MVC 2 and attempt to get my company to adopt it as a viable platform for future development, I have been doing a lot of reading lately. Having worked with ASP.NET pretty exclusively for the past few years, I had some catching up to do.
Currently, I understand the repository pattern, models, controllers, data annotations, etc. But there is one thing that is keeping me from completely understanding enough to start work on a reference application.
The first is the Service Layer Pattern. I have read many blog posts and questions here on Stack Overflow, but I still don't completely understand the purpose of this pattern. I watched the entire video series at MVCCentral on the Golf Tracker Application and also looked at the demo code he posted and it looks to me like the service layer is just another wrapper around the repository pattern that doesn't perform any work at all.
I also read this post: http://www.asp.net/Learn/mvc/tutorial-38-cs.aspx and it seemed to somewhat answer my question, however, if you are using data annotations to perform your validation, this seems unnecessary.
I have looked for demonstrations, posts, etc. but I can't seem to find anything that simply explains the pattern and gives me compelling evidence to use it.
Can someone please provide me with a 2nd grade (ok, maybe 5th grade) reason to use this pattern, what I would lose if I don't, and what I gain if I do?
In a MVC pattern you have responsibilities separated between the 3 players: Model, View and Controller.
The Model is responsible for doing the business stuff, the View presents the results of the business (providing also input to the business from the user) while the Controller acts like the glue between the Model and the View, separating the inner workings of each from the other.
The Model is usually backed up by a database so you have some DAOs accessing that. Your business does some...well... business and stores or retrieves data in/from the database.
But who coordinates the DAOs? The Controller? No! The Model should.
Enter the Service layer. The Service layer will provide high service to the controller and will manage other (lower level) players (DAOs, other services etc) behind the scenes. It contains the business logic of your app.
What happens if you don't use it?
You will have to put the business logic somewhere and the victim is usually the controller.
If the controller is web centric it will have to receive its input and provide response as HTTP requests, responses. But what if I want to call my app (and get access to the business it provides) from a Windows application which communicates with RPC or some other thing? What then?
Well, you will have to rewrite the controller and make the logic client agnostic. But with the Service layer you already have that. Yyou don't need to rewrite things.
The service layer provides communication with DTOs which are not tied to a specific controller implementation. If the controller (no matter what type of controller) provides the appropriate data (no mater the source) your service layer will do its thing providing a service to the caller and hiding the caller from all responsibilities of the business logic involved.
I have to say I agree with dpb with the above, the wrapper i.e. Service Layer is reusable, mockable, I am currently in the process of including this layer inside my app... here are some of the issues/ requirements I am pondering over (very quickly :p ) that could be off help to youeself...
1. Multiple portals (e.g. Bloggers portal, client portal, internal portal) which will be needed to be accessed by many different users. They all must be separate ASP.NET MVC Applications (an important requirement)
2. Within the apps themselves some calls to the database will be similar, the methods and the way the data is handled from the Repository layer. Without doubt some controllers from each module/ portal will make exactly or an overloaded version of the same call, hence a possible need for a service layer (code to interfaces) which I will then compile in a separate class project.
3.If I create a separate class project for my service layer I may need to do the same for the Data Layer or combine it with the Service Layer and keep the model away from the Web project itself. At least this way as my project grows I can throw out the data access layer (i.e. LinqToSql -> NHibernate), or a team member can without working on any code in any other project. The downside could be they could blow everything up lol...
I've been a longtime ASP.NET developer in the web forms model, and am using a new project as an opportunity to get my feet wet with ASP.NET MVC.
The application will need an API so that a group of other apps can communicate with it. I've always built API's out just using a standard web service prior to this.
As a sidenote, I'm a little hesitant to plunge headfirst into the REST style of creating API's, for this particular instance at least. This application will likely need a concept of API versioning, and I think that the REST approach, where the API is essentially scattered across all the controllers of the site, is a little cumbersome in that regard. (But I'm not completely opposed to it if there is a good answer to the potential versioning potential requirement.)
So, what say ye, Stack Overflow denizens?
I'd agree with Kilhoffer. Try using a "Facade" wrapper class that inherits from an "IFacade". In your Facade class put your code to consume your web service. In this way your controllers will simply make calls to the Facade. The plus side of this being that you can swap a "DummyFacade" that implements the same IFacade interface in that doesn't actually talk to the web service and just returns static content. Lets you actually do some unit testing without hitting the service. Basically the same idea as the Repository pattern.
I would still recommend a service layer that can serve client side consumers or server side consumers. Possibly even returning data in a variety of formats, depending on the consuming caller.