Can anyone tell me what the need/advantage is to using a web service with an asp.net gui and using Linq to SQL? The web service layer seems unnecessary. Linq to SQL is completely new to me and I am researching as I am setting up a new project. Does anyone have any experience with this?
You would expose services for those cases in which other applications may need to access your data (such as a smart client, another application, a winforms app, etc.). A lot of people will develop using web services to prevent themselves from having to restructure to web services in the future.
In almost any professional/enterprise web application you want to separate the UI tier from the data access layer so you would not embed Linq to SQL calls in the UI tier. Instead you would have a service tier in between, whether its web services, WCF, or just a DLL with business logic that orchestrates your data access layer. Independent tiers are easier to maintain, update, refactor, and learn so the up front investment in creating them is worth the effort.
It is certainly not necessary, but can be handy in case you want to keep your data access layer on a separate server from your presentation server (ASP.NET). A web service allows you to restrict communication between the two servers to only port 80.
Note that this could apply to plain old ADO.NET or anything else too.
Webservices became a separation layer because they were intended as a platform agnostic way of sending data to other software. They are websites that serve information to other software and not directly to the user.
A webservice is an overhauled separation layer for a website and can not completely replace a good data, business logic and UI separation.
Do it as your logic tells you to, but beware of the performance drops that you pay if you do not need to communicate to other software.
Completely agree with Ovidiu Pacurar. Web services are NOT a good choice for modeling layers of concern. You should do this using good old fashioned OO design. There is no reason for a web application to call web services within itself for data access unless they are intended for client ajax calls or if you need to run the business/data layer on another server for extreme security concerns.
Agreed with previous poster. You'd probably want to do this to apply the "Separation of Concerns" idea...
Related
I'm creating a web-application and decided to use micro-services approach. Would you please tell me what is the best approach or at least common to organize access to the database from all web-services (login, comments and etc. web-services). Is it well to create DAO web-service and use only it to to read/write values in the database of the application. Or each web-service should have its own dao layer.
Each microservice should be a full-fledged application with all necessary layers (which doesn't mean there cannot be shared code between microservices, but they have to run in separate processes).
Besides, it is often recommended that each microservice have its own database. See http://microservices.io/patterns/data/database-per-service.html https://www.nginx.com/blog/microservices-at-netflix-architectural-best-practices/ Therefore, I don't really see the point of a web service that would only act as a data access facade.
Microservices are great, but it is not good to start with too many microservices right away. If you have doubt about how to define the boundaries between microservices in your application, start by a monolith (all the time keeping the code clean and a good object-oriented with well designed layers and interfaces). When you get to a more mature state of the application, you will more easily see the right places to split to independently deployable services.
The key is to keep together things that should really be coupled. When we try to decouple everything from everything, we end up creating too many layers of interfaces, and this slows us down.
I think it's not a good approach.
DB operation is critical in any process, so it must be in the DAO layer inside de microservice. Why you don't what to implement inside.
Using a service, you loose control, and if you have to change the process logic you have to change DAO service (Affecting to all the services).
In my opinion it is not good idea.
I think that using Services to expose data from a database is ideal due to the flexibility it provides. Development of a REST service to expose some or all of your data as a service provides flexibility to consume the data directly to the UI via AJAX or by other services which can process the data and generate new information. These consumers do not need to implement a DAO and can be in any language. While a REST Service of your entire database is probably not a Micro-Service, a case could be made for breaking this down as Read only for Students, Professors and Classes for exposing on the School Web site(s), with different services for Create, Update and Delete (CUD) available only to the Registrars office desktop applications.
For example building a Service to exposes a statistical value on data will protect the data from examination by a user/program who only needs a statistical value without the requirement of having the service implement an entire DAO for the components of that statistic. Full function databases like SQL Server or Oracle provide a lot of functionality that application developers can use, including complex queries(using indexes), statistics the application of set operations on data.
Having a database service is a completely valid pattern. In fact, this is one of the key examples of where to start to export aspects of a monolith to a micro service in the Building Microservices book.
How to organize your code around such idea is a different issue. Yes, from the db client programmer's stand point, having the same DAO layer on each DB client makes a lot of sense.
The DAO pattern may be suitable to bind your DB to one programming language that you use. But then you need to ask yourself why you are exposing your database as a web service if all access to it will be mediated by the same DAO infrastructure. Or are you going to create one DAO pattern for each client programming language binding?
If all database clients are going to be written on the same programming language, then are you sure you really need to wrap your DB as a microservice? After all, the DB is usually already a remote service with a well-defined network protocol optimized to transfer data fast and reliably. Why adding HTTP on top of it? What are you expecting to gain from adding such complexity?
Another problem with using the DAO pattern is that the DAO structure does not necessarily follow the evolution of the web service. The web service may evolve in a way that does not make old clients incompatible. You may have different clients using different features of the micro service. In this case you are not sharing the same DAO layer structure on each client.
Make sure you are not using RPC-style programming over web services, which does not make much sense. You will be basically throwing away one of the key advantages of micro services, which is the decoupling between service and client.
This post http://www.theserverside.net/tt/articles/showarticle.tss?id=Top5WSMistakes
encourages me to create the web service for business logic layer but many people use it in the data access layer.
I want to create a project where i want to access the same data repository from a desktop application, website and a cell phone. What would you recommend me?
Is there any case it may be a good idea to implement web services to both layers?
The question is too open ended so the answer is: it depends.
What needs do your applications have for the data? Is it just data access or some business logic involved? If it is just accessing of data, do you really want the client to have direct control over it? How similar are the three applications? Do they share functionality or just data?
As I see it there are two main paths you can chose:
1 - expose a web service for the business, with the data hidden behind the web service. This is a good setup if the three clients (I'll call the desktop app, web app and cell phone "clients" since that is what they are) share functionality (i.e. they are different views for the same business model). This avoids duplicating similar business logic in all the clients;
2 - expose the data directly with a web service. This is a good setup if the three clients have nothing in common but just use the same data for different purposes. But in this case, with the three sets of business logic, where are you going to put the logic? In the clients? How will that work for the desktop application (considering you install this desktop app 300 times or so)? You again need some service and the clients to be thin clients not thick ones.
If you take 1) and 2) into consideration you will see that usually it is better to have a service layer in front of your data.
Going back to the "it depends", analyze your special needs first and only then choose the solution that is best suited for your situation.
How about a point 3? make your data access layer into a library (.jar, .dll or whatever technology you are using) and make that available to the (1? 2? 3?) business web services that serve your clients?
Currently inside my organization we are trying to come up w/ some conventions for a pilot SOA project. At first glance we thought it would be best to force users of the service to use the business service w/out direct access to any data endpoints .. but are there specific scenarios where this is not true or it might be "valid" for developers to have access to specific data endpoints outside of a service?
I always fear that if we open this up, it will actually hurt reuse because everyone will just "re-invent" similar business services using the same back-end data as it's available and would be "in theory .. easier" to just write a new business service rather than ask "what does this other service do that uses my database?"
Because even if the service is almost a direct pass through to the database we would have the ability to apply rules that would save developers time and ultimately the business money.
Thoughts?
Wouldn't your webservice just be a thin wrapper for your business layer anyway? Your service layer probably shouldn't have anything more than your business layer besides some dumbed-down DTOs perhaps. Then noone is asking "what does this other service do that uses my database?" because it isn't using your db, it is using your BL.
You're waving a red flag when you describe "forcing" users to do anything. Maybe you can think about your question and rephrase it in terms something like "enable" users, because this should be the starting point for your decision, and SOA offers advantages and disadvantages for different UI strategies.
Not having dealt much with creating web-services, either from scratch, or by breaking apart an existing application, where does one start? Should a web-service encapsulate an entity, much like a class does, or should the service have more/less to it?
I realize that much of this is based on a case by case analysis of what the needs are, but are there any general guide-lines or best practices or even small nuggets of information that web-service veterans can impart to a relative newbie?
Our web services are built around functional areas. Sometimes this is just for a single entity, sometimes it's more than that.
For example, if you have a CRM, one of your web services might revolve around managing Contacts. Creating, updating, searching for, etc. If you do some type of batch type processing, a web service might exist to create and submit a job.
As far as best practices, bear in mind that web services add to the processing overhead. Mainly in serializing / deserializing the data as it goes across the wire. Because of this the main upside is solely in scalability. Meaning that you trade an increased per transaction processing time for the ability to run the service through multiple machines.
The main parts to pull out into a web service are those areas which are common across multiple applications, or which you intend to expose publicly, or which would benefit from greater load balancing.
Of course, you need to analyze your application to see where any bottlenecks really are. In some cases it doesn't make sense. For example, if you have a single application that isn't sharing its code and/or the bottleneck is primarily database related.
Web Services are exactly what they sound like Services for the Web.
A web service should be built as an API for the service layer of your app.
A service usually encapsulates an entity larger than a single class.
To learn more about service layers and refactoring to add a service layer read about DDD.
Good Luck
The number 1 question is: To what end are you refactoring your application functionality to be consumned as a bunch of web services?
a. What are the things I must consider?
b. I have several Stored Procedures being execute by the current application. If I create equivalent methods to execute these procedures, what would be the risk or the challenge.
Architecturally, one thing you must consider in transforming a web app to a web service is that local access to methods and data is not the same as remote access. Remote access should be designed so that invocations are more course-grained and exchange more information at once.
Another thing you would need to think about is what your serialization protocol you will use. For example, SOAP vs a REST-based protocol.
Also, think about security - the security considerations are different between a web application and a web service.
Finally, think about how others will know about your web service (or if they will at all).
One risk is ensuring that your code remain the same.
What I mean by this is that there is a distinct possibility of code duplication in this situation, and as such means that you may inadvertently forget to modify one of the places where the Stored Procedure is used (say if you add a new variable to the stored proc call).
Then you also must consider security. For example, exposing a web service call that provides a list of users to the wild is probably not that good of an idea. you need to plan for how you're going to pass/receive authentication & authorization information.
Managing your code base as Stephen said is going to be a big challenge if you create equivlant methods. Your much better off extrapolating the methods into a new library, that both the web application and web service will use. Your web apps shouldn't have any data access code in them.
With a web service you need to consider your clients. Who is going to access your data and from where. If for example its from a .net windows client on the same network or machine a TCP binding might be best. Or if you need to support older .net framework clients or even java clients you need to be careful about what technology you use.
You will also want to choose between WCF or ASMX. Which the previous paragraph shouuld help answer.
It seems to me that the greatest challenge will be that you are obviously tempted to do this. I think you're making a mistake.
Your web application, and the web service you propose, have different requirements. By "transforming" the application into the service, you will burden the service with the requirements of the application.
Here's a "thought experiment": what if you were to write the service from scratch, ignoring the application. How similar would the service and application be? If they would wind up alike, then transformation would make sense. Otherwise, not so much.