Is it "acceptable" to have an ASP.Net 2.0 application without the BLL (Business Logic Layer) as the following?
SQL Server Data Storage & Stored Procedures
Data Link Layer (Strongly Typed Table Adapters) connecting to Stored Procs
Presentation Layer ASPX Pages with Code behind and ObjectDataSource for connection straight to the DLL
Is a BLL always preferable, even if business logic is entirely validatable in the presentation's code behind? What are the potential drawbacks for not using a BLL?
It's acceptable as long as you understand the consequences. The main reason you'd have a BLL is to re-use that logic elsewhere throughout your application.
If you have all that validation logic in the presentation code, you're really making it difficult to re-use elsewhere within your application.
Like everything else it is environmental and depends on the use of the system. The question you need to ask your self is:
Will this be actively developed
Is this going to be used over the course of many years and expanded on
Is the expansion of the application unknown and thus infinite
Really it comes down to laziness. How much time to do you want to spend reworking the system from the UI? Because having no business layer means duplication of rules in your UI across possibility many many pages.
Then again if this is a proof of concept or short demo or class project. Take the easy way out.
Acceptable? Depends who you ask and what your requirements are. Is this app an internal one-off used by you and a few other people? Maybe this is good enough. If it's meant to be a production ready enterprise application that will grow and be maintained over the years, then you probably want to invest more effort up-front to build a maintainable app.
Separation of Concerns is a key design technique for building maintainable apps. By mixing presentation, business, and data access logic all together, you can end up with a very fragile difficult to change application architecture.
It depends. If your business logic is in your click events and page loads, it is NOT acceptable.
It appears that your business logic is somewhere within the DAL (e.g., stored procedures and such), just as long as you are consistent, it's fine. As long as you are very, very sure that your clients will always be using SQL Server then this approach is not a problem.
I know a colleague who has all his business logic in stored procedures that his views are mostly thin clients to database backends: he has been immensely successful with the product that he sells. But that's only because he's very consistent with it.
If the application is a general one, then the business logic layer can be used in complete other applications too. Like, I normally use my CMS related BLL classes in other applications.
Related
Team A has an enterprise app that uses ADO.NET for data access that executes stored procedures. The data access is encapsulated in it's own project (let's call it DAL.dll)
Team B is creating another unrelated app that's reusing the stored procedures in the enterprise app. This app is currently using the MS application block for data access. The issue we run into is that whenever Team A make any change to the input/output params in the stored procedures, there is a runtime error in Team B's app and this app needs to be updated to accommodate the additional params (or params that were removed). So, most of these go unnoticed until a user complains. At the very least, we would like to have the app throw a compilation error so that the build process warns us of the changes made.
One way to do this is to have Team B's project add a reference to the DAL.dll
I'd like to know if there are any other cleaner ways of solving the issue. We are ready to replace Team B's MS Data application block to use a different technology (Entity Framework?) if necessary.
Among the other answers, I'd strongly suggest getting those stored procedures into source control, in a Database Project. You then may be able to use the features of your source control system to do several things:
Lock some of the code so that it cannot be changed
Give you notifications if the code is changed
Warn you if the stored procedures change in a way that would prevent them from being called
Branch the stored procedures so that each team can have their own version of changed code, while keeping the unchanged stored procedures common. You of course will need to separate the different versions in the database.
I agree with the other posters on this thread that you should not share stored procedure's across different .NET DLL's, that is just a recipe for disaster. I would also shy away from ORM's like Entity Framework if you are doing anything at all complicated with your database schema because ORM's excel at getting a simple object model translated from your .NET application classes into SQL tables and SP's, but traditionally do poorly at optimizing them for performance on the database side. There will be people who claim otherwise, and they may have a valid point if you are an expert in wrangling an ORM to do waht you want like they are, but chances are you are not and it will cause you headaches in the long run.
A shared data access layer might work, but conceptually you are then just changing the implementation of the dependency from some code that a DBA wrote to some code that a .NET programmer wrote. Yes, you can use integration tests to achieve better verifiability, but the same case could be made for SQL with tools like Red Gate's SQL Test. I would shy away from this approach if the two applications are already experiencing some sort of pain from sharing SP's. That is an indication that the dependency just should be done away with.
If it were up to me, I'd just make a new schema for Team B's app. You can read more about schemas in SQL Server here: MSDN Schema description for 2008 R2. You can think of them as namespaces for SQL Server but with some additional bells and whistles like permission and access control. Separating out your different applications into separate schemas on the same shared database will probably make for the most flexible implementation in the long run.
unrelated app that's reusing the stored procedures in the enterprise app
If these two application are really unrelated why are those sharing procedures or even the same database. I know this is a long read, but I recommend you to read this: A Better Path to Enterprise Architectures
The partioning concept in there relates to the bounded context in Domain driven design:
Multiple models are in play on any large project. Yet when code based on distinct models is combined, software becomes buggy, unreliable, and difficult to understand. Communication among team members becomes confusing. It is often unclear in what context a model should not be applied.
Therefore: Explicitly define the context within which a model applies. Explicitly set boundaries in terms of team organization, usage within specific parts of the application, and physical manifestations such as code bases and database schemas. Keep the model strictly consistent within these bounds, but don’t be distracted or confused by issues outside.
It is expected you end with problems when you don't explicitely deal with this. You're lucky you're seeing early failures, as it can turn into problems much harder to find on the long run.
Analyze the problem again with the above in mind. Consider if you're missing some explicit context where this common functionality should live.
My question is: which team owns the store procedured and the database shared? Usually as a good architecture/design, you should not have two different apps sharing same database / procedures.
A better way to share data/functionality between two different applications is through a services or API, so the team who owns the functionality would be responsible to maintain it.
Also, have a good communication between both teams is highly recommend.
Depending on the owner of the DAL project, you could host web services and share the API. That way, you separate the Data Access Layer from the business logic, which allows anyone to use the same DAL without having to publish it to each different location.
From my point of view, it looks like both Team A and Team B should share the same core model and look at Multitier architecture as a possible solution.
It sounds like it would make sense to create a shared DAL that both applications can share.
I would add unit tests (or really integration tests) to make sure the DAL is compatible with the apps after changes. That way your tests would fail if incompatible changes have been made
"I'd like to know if there are any other cleaner ways of solving the issue."
The cleanest way is for Team B to sit down with Team A and encapsulate the relevant business logic into a shared API. It doesn't matter so much how you implement that API; what does matter is that the API's interface is documented and versioned so everyone knows what to expect.
One reasonable mechanism for this in a .NET environment is to use Microsoft's WebAPI.
In short, the question of "how do we share a stored procedure?" is most likely looking at the wrong level of abstraction.
My company has a fairly old fat client application written in Delphi. We are very interested in replacing it with a shiny new web application. This will make maintenance a breeze and many clients want a web application.
The application is extremely rich in domain knowledge, some of which is out of our control. Our clients use the program to manage their own clients and report them to the government. So an inaccurate program is a pretty big thing. The old program has no tests. We are not sure yet if we will implement automated testing with the new one.
We first planned to basically start from scratch. But we are short handed and wanting to basically get everyone on the web as soon as possible. So instead of starting from scratch we've decided to try to make use of the legacy fat-client database.
The database is SQL Server and can be used in SQL Server 2008 easily. It is very rich in stored procedures, functions, a few triggers, and lots of tables with over 80 columns... But it is decently normalized. We want for both the web application and fat client to be capable of using the same database. This is so that if something breaks badly in the web application, our clients can still use the fat client and connect to our servers. After the web application is considered "stable", we'd deprecate the fat client.
Has anyone else done this? What tips can you give? We want to, after getting everyone on the website, to slowly change the database structure to take care of some design deficiencies. What is the best way to keep this in a data access layer so that later changes are easy?
And what about actually making the screens? Is there any way easier than just rewriting an 80 field form in ASP.Net? Are there any tools that can make this easier?
The current plan is to use ASP.Net WebForms (.Net 3.5). I'd really like to use MVC, but no one on the team knows it including me.
We are not sure yet if we will implement automated testing with the
new one.
Implement automated testing. What's the point in replacing one buggy program with another?
Good question, but "Slowly change" the db structure after getting everyone on the website, sounds like a joke...
I would rather take the opportunity to create a fresh db structure, write a bulletproof migration script for you db, that you can try out and rewrite a zillion times without any side effect fro your clients, and then write whaterver you want (fat/web) on the new db, have it tested and migrate everyone when it's ready.
I have a couple suggestions:
1) create a service layer to abstract away the dependance on the DAL. In a situation as you describe having a layer of indirection for the UI and BLL to rely on makes DB changes much safer.
2) Create automated tests (both unit and integration), especially if you plan on making fairly significant changes to the Domain or Persistance layers (BLL/DAL). To make this really easy you should always try to program to an interface. This makes your code more flexible as well as letting you use mocking frameworks (Moq is one I like) to ensure your tests truely are unit tests and not integration tests.
3) Take a look at DDD (http://domaindrivendesign.org/) as it seems to fit pretty well with the given scenario. At the very least there are some very useful patterns that can help make your application more flexible.
4) MVC isnt very hard to learn at all, it is however an easy way to get unit testing setup for the UI as a result of the MVC architecture (testing the controller and not the view). That said, there is no reason you couldn't unit test web forms, its just a bit more work. MVC really is just a UI framework/design pattern (more Model2 but we can ignore that for now). It gets you closer to the metal so to speak as you will be writting a lot more HTML and using a Model (the 'M') for passing data around.
For DDD take a look at Eric Evans book: http://www.amazon.com/Domain-Driven-Design-Tackling-Complexity-Software/dp/0321125215/ref=sr_1_1?s=books&ie=UTF8&qid=1317333430&sr=1-1
Hope that helps
ASP.NEt forms is a no starter, is completely inappropriate for something like this. I recommend to start with something like Creating an OData API for StackOverflow including XML and JSON in 30 minutes, then build your Web app on top of that (ie. push it to the client, use JQuery/Silverlight).
i.e. Is MVP still the next best choice when MVC is not an option?
I thought I'd ask this here as I'm sure there are others like me who don't have the luxury of being on a green-field project and want to refactor a webforms UI to better separation of presentation from business objects...
I'm working on a legacy application tasked with adding relatively small additional requirements, enhancements, and bug fixes.
The part of the application I'm addressing here may be characterised as the UI for a set of CRUD operations over business objects that are persisted to a relational database.
The existing UI uses a MultiView control to navigate between the editing of associated business objects (one-one associations or one-many / parent-child). Yes, that's right - all on one page. Unfortunately there is very sparing use of UserControls so the markup and code-behind is hundreds of lines long.
On each View a FormView manages the CRUD over the business objects via various ObjectDataSources. Within the ItemTemplate of each FormView various server controls databind to fields or methods on an ObjectDataSource.
I'd like to introduce more separation of concerns and get some of the reams of code out of Page code-behind.
My research so far suggests to me that I might consider:
Use a flavour of Model View Presenter; more specifically - use an ObjectContainerDataSource from the Web Client Software Factory to make it easier to bridge between the current UI and a set of new Presenter classes.
Build again from scratch with an MVC framework (not an option).
Leave well alone; an MVP pattern is only justified if I need to re-use my Presentation in different UI scenarios?
If I settle with (3) I'd still like to know how to start refactoring towards better separation of presentation.
What would you do? any other ideas gratefully received...
Here's some more background for anyone who's interested:
The domain is in pharmaceutical research but that's fairly irrelevant and you can think of it as pretty typical line-of-business - user configuration of a family of settings that form the operating conditions of another part of the application.
The business object layer has already been built in a very consistent manner. Although I may not like it, I can't neccesarily justify changing it. Each object is it's own Repository / Data Access Object in that there are static methods for 'get by ID' and 'get list by criterion'. Where possible common operations are implemented in an abstract base class. Each business object delegates the data access work to a Data Access Layer that makes use of ADO.NET 2.0 Provider Factory mechanisms to remain relatively abstracted from a concrete Provider. In this respect it shares a lot in common with any app that uses the Data Access Application Block from the Microsoft Enterprise Library.
There are fairly exhaustive integration tests written in NUnit that set up a test database from scratch so they take ages to run but at least they verify that stuff works as it should (at some point in the past anyway ;-). There is almost no true unit testing in place (yet).
WebForms now has an emerging effort in the form of the ASP.NET Web Forms MVP project
"...there are still a host of
compelling advantages to ASP.NET Web
Forms.
The ASP.NET Web Forms MVP project is
... an approach that facilitates
separation of concerns and testability
whilst maintaining the rapid
development that Web Forms was built
to deliver"
Rob Conery has concerns that this may be a wasted effort and an unneccesary distraction now that we have MVC but at this stage I still think the source code is worth a look...
http://haacked.com/archive/2006/08/09/ASP.NETSupervisingControllerModelViewPresenterFromSchematicToUnitTestsToCode.aspx has a good example of doing MVP with webforms. The advantage is not just that your UI is decoupled from BL - the real treat is that you can write tests for the code.
I am Developing a mid-size application and want to implement Application Architecture, I've read some Architecture Books and Approach and think about
AAFN (Application Arcitecture For .net) presented by Microsoft
SOA
SDLM
SDO
MVC
and vice versa ...
this is a web application that will extended with some other small application ( just think about something like a M.I.S with a (or two) core)
Whitch Projects I should have I think about
Common // to use in all projects
Framework // main framework
DAO // data access object ( entityframework or nHibernate )
UI // will available in 2 variant web and windows(wpf) interface )
BusinessEntities // all subApplication project logic will goes there
ApplicationNameProject // each application have their Own Logic (in BussinessEntities)
ApplicationUnit // each application Entity will place here
ApplicationNameProject // each application data Entity (in Application Unit)
Services // WCF Services goes here to contribute with all applications
this is the architecture witch I think about, I do not have any force to use this, I want to know whats the best fit for me, can Change all of it or add some other projects and remove these projects
any help appriciated
There is no "best small or mid-size application architecture" as a silver bullet to fit any project, so drop that idea right now or you'll be in for a world of pain down the road.
The architecture for any given project will fit the purpose of that project. In some cases, ASP.NET WebForms with a direct queries into the database will be the most appropriate architecture, in some cases MVC will be the right architecture, in some cases a windows forms application built on top of a web service that connects to a relational database through an ORM like LINQ-to-SQL or NHibernate.
You can't decide on a one-architecture-fits-all approach, it just doesn't work. Each architecture has its merits and weaknesses and thus projects for which it is well suited and projects for which it should be avoided. You should pick the approach that makes the most sense for the current project/scenario.
Given that however, I tend to take a fairly uniform approach.
If I need a quick utility project that does a very specific thing and is highly unlikely to be needed for anything else, I might use a console application with queries against my database hardcoded.
If I need a common set of queries that I'm likely to need from multiple projects, I'll write them as stored procedures to get the performance benefits and build a data access layer that will leverage these stored procedures to give me standardized business objects, in a standard DAL (data access layer)/BOL (business object layer)/BLL (business logic layer) approach. This is advantageous because it means that once I've got this set of libraries built I can float any application over the top - for instance a webforms or MVC application.
MVC is advantageous because of separation of concerns - your controller can interact with your business library simply to access the data it needs and your views are really just that - a view of the data that the user can interact with. The views do nothing more than take the current data view to the user and transport any data changes back from the user to the controller - no logic is held in the view and as such it means that it's far easier to unit test and make changes to components without affecting the rest of the application.
The drawback to a multi-tiered or multi-layered approach like this though is that it takes time to architect it properly and if you're only after a throw-away utility application like they demonstrate on stage at developer conferences then this is complete overkill and I wouldn't bother with it.
Think of it like this: Every layer, every library, every component requires justification. If there is less justification for than against, then don't do it. The key is not to do something without reason - anything you do is correct providing that you have a well thought out reason for it, and by well thought out, I mean that you've found very good reasons for and against and you've made an educated decision, you've not made a decision based on half thoughts, or worse, no thought at all.
Anything but the most trivial .NET application should have several projects: a UI layer, some kind of business logic layer, a persistence (storage) layer and accompanying test projects. Each project should interact loosely through interfaces.
In general you should create the minimum number of layers you need to make your code testable and easy to understand.
To figure out what the minimum is that you need it can be a good idea to let your tests drive the internal design of the system. Each layer should have tests in its own right, with (possibly) the exception of the top HTML layer and the bottom SQL layer.
With that in mind it helps to separate concerns as far as possible. For example SQL queries should almost never be in the same block of code as HTML support: split things into multiple layers that each do one and only one thing. This makes changes easier.
Be aware of the difference between systems architecture (where loosely coupled Web services using e.g. REST interact) and the internal design of the system. It's a good idea to decouple the Web service interfaces (as consumer or provider) in their own layers as this is an area that often changes.
These designs are an art that's best learned by practice. With good unit tests you should find refactoring an application design fairly swift, so it's a good idea to look at technologies like Spring.NET or other inversion of control containers to make this easy.
I'm thinking about going into the ASP.NET MVC scene.
I've seen the videos at http://asp.net/learn, but they havn't impressed me.
So can you answer me, what makes MVC "so impressive", and why does it make life better and easier?
ASP.NET MVC is much more in tune with the technology on which it is layered. ASP.NET Forms attempted to pretend that there was a nice fat stateful infrastucture as there is in a standard WinForms app. However HTTP and Web servers do not like fat stateful applications.
ASP.NET MVC allows for a separation of concerns. The request is processed by a controller not a "Web Page", it chooses how to respond and what UI is needed to present that response. The controller builds the set of structured data needed by its choice of view then hands over that data to the view.
This division allows much easier testing, the view is merely a means to present what should be a complete well munged chunk of data. Its way easier to build a test for something which takes structured data in and responds with structured data.
ASP.NET Forms is almost impossible to test in this way (especially without expensive tools claiming to achieve it). Hence an MVC application is easier to get right and much easier to ensure it stays right by consistently running existing tests.
Caveat: The major draw back of ASP.NET MVC right now is lack of solid documentation. I've been assured that docs are coming "soon".
Have you ever worked on a large project that had great intentions when it started but 3 years later was a complete mess?
MVC is a just pattern it can be misused the same as ASP.NET is misused. It is just harder to do.
Model–View–Controller (MVC) is an
architectural pattern used in software
engineering. Successful use of the
pattern isolates business logic from
user interface considerations,
resulting in an application where it
is easier to modify either the visual
appearance of the application or the
underlying business rules without
affecting the other.
It allows you to separate your logic in a way that makes sense to most people. While at the same time it lends itself well to testing.