I am making asp.net site using Layered architecture. Can I implement and use Data-Set object in presentation layer?
I simple layered architecture might have:
Datasets being populated in the DAL
Business Entities / Domain objects in the 'BLL' are populated from the DAL Datasets
The presentation objects are pretty simple data transfer objects that match whatever is being presented.
Obviously there is a bit more to it than this.
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Data Access Layer and Business Logic Layer is better place for it. To get more insight try Creating a DAL and Creating a BLL.
Obviously You can use it, but layered architecture is all about separating layers.
For interacting with database, you should use Data Access Layer.
You can have a look the aim of data access layer.
What is the purpose of a Data Access Layer?
Related
I have a ASP.NET MVC solution with three projects:
SquarkMVC
SquarkBLL
SquarkDAL
The SquarkDAL layer has Linq2SQL classes for each object in the DB. BLL references the DAL in order to conduct business logic on the DB.
My question is this... without having to reference the DAL in the MVC layer, how should I model the entities of the DB in the MVC layer? For instance, if I have a sign up form in the MVC layer, what is the best way to take that information, pass it to the Business Layer which then passes it on to the Data Layer? I don't want the MVC layer to know anything about the DAL.
I've found this answer on another post... is it generally agreed that the best way to overcome this is to create a transfer object in order to pass the information from the presentation layer, to the business layer, which will then convert the information into the entity classes used by the DAL?
Hope this makes sense.
Using objects is a common way to do this. Usually DTOs (Data Transfer Objects) are "dumb" POCOs having a set of properties, and acts like a "struct", but, if you put on them validation and more logic (view logic) you have a view model and you can use them to work with the controller. This one should use the model (of the Business Layer).
More, Business Layer should never having a reference to the DAL, because your business model should be independent by the storage.
Instead, the data access layer should reference the model, and choose the right way for persistence. You can achieve it with the Repository pattern.
Anyway there are a lot of books about domain driven design.
So I am thinking of using LLBLGen Pro and Spring.Net on this asp.net project using a service layer to decouple the Business Logic from the Data Store. I am also considering using PONOS in the UI Layer, now my question is:
Should I Map the rich LLBLGen Entity Objects to Ponos in the Data Layer or in the Service Layer? If I do it in the Data Layer then I loose all their rich functionality in the service layer. Or should I just skip the mapping to Ponos and use LLBLGen entities all the way through? If the later it will be harder to test it right?
Can someone give me pros and cons of both approaches?
Thanks
The upside of using LLBLGen Entities with no mapping is that you get entities generated right from your database schema (or even with no database schema in LLBL 3.x), so you can have a very usable entity model in a matter of minutes. The downside is that your entities inherit from LLBL framework classes, which makes them harder to enrich with behavior/business logic. If you generally design your biz logic as a set of services, this won't pose a problem.
I don't see testing as a problem in this scenario, as I generally view the entities as "anemic" data objects, and I generally don't mock such objects (no real reason to do so).
The upside of mapping to POCOs is that you have full control over the design of your domain/entity/DTO objects, and they can be as rich or as anemic as you want. The downside is that you will have to design and code the POCO classes and the mapping, and (as you said) you will lose some functionality like change tracking that is built into LLBL Entities.
I personally choose to use the generated entity objects unless I have a very good reason NOT to.
While designing (and then implementing) a layered application:
Is it correct to use the same ORM objects accross all layers? (which would go against encapsulation).
Or the presentation, business and data layer should each have their own objects? (which would lead to lots of code repetition).
e.g. (just to illustrate the question): if one uses Linq to SQL in the Data Layer and Visual Studio's O/R designer to generate the ORM objects, are those objects supposed to be used in the Business and Presentation Layers as well.
i.e.: Are the objects associated with the entities that the application handles a crosscutting issue?
It depends by your business. if you are talking about a small application you could do it.
Usually the best practices wants to don't expose the entity from the DAL to the presentation because doing that the layer are going to be tightly coupled and you could expose data that doesn't make sense at the top layer (presentation)
on the other hand you shouldn’t create a bunch of object per each layer.
it's always hard answer this question because it really depends by your needs.
you can have a look at this book just to have an idea about
http://books.google.co.uk/books?id=FyWZt5DdvFkC&printsec=frontcover&dq=martin+fowler+enterprise+architecture&source=bl&ots=eEEx4ATr5C&sig=sSmDmffOSALWfFZEaPyhkwwEq_I&hl=en&ei=SJnSTMuSJIHm4AaK9tW5Dw&sa=X&oi=book_result&ct=result&resnum=6&ved=0CDAQ6AEwBQ#v=onepage&q&f=false
i read in one article that its not a good practice to pass dataset between different layers of .net web application.(DAL->BAL->Pages vice versa).Is that correct?
please give your suggestions.
Thanks
SNA
On the one hand, the problem with datasets and datatables is that they expose database implementation details like column names and types outside of your data access layer. Change a column name in your database or query and odds are that change is propogated to your dataset as well, forcing a re-compile of any tier that uses the dataset. So if you retrieve data into a dataset you should convert it to use strongly-typed business objects before passing it on.
On the other hand, a dataset doesn't care what kind of database it belongs to. You can use them with access, oracle, sql server, mysql, anything. So there is some generic-ness there that can make them useful when passing data between tiers. And just like the business layer shouldn't care about database details the data layer shouldn't really need to know what the the business objects are, so there's a good argument that you should use them for data interchange at that level.
My normal procedure is to have a sort of one-way "translation" tier between the business and data access layers, so that the business layer only deals with business objects and the data layer only returns generic data. This currently takes one of two forms:
I'll write my data access methods to return datatables or datareaders, the the translation tier will use a factory pattern to convert those rows into the desired strongly-typed business objects.
or
I'll use C# iterator blocks to convert a datareader into an IEnumerable<IDataRecord> in the data access layer and the translation tier will use them to change that IEnumerable<IDataRecor> into an IEnumerable<MyBusinessObject>, such that the code only ever iterates over the result set one time.
There is nothing wrong with passing around datasets but it's not a great practice.
Pros:
Easy to pass around and use in .NET apps
No having to code wrapper classes
Lots of functionality built into DataSets
Cons:
Data type that is not really type safe.
Your data field names can change all parts of your app will compile fine until they blow up at runtime.
Heavy object. Dataset does a ton of stuff and you probably don't need 90% of it.
Having non .NET apps talk to your DAL or BAL is going to be very clean.
There's nothing wrong about passing DataSets from your DAL to your BAL.
I think this stackoverflow question on DAL best practices sums up the two schools of thought pretty well.
I am in the middle of a "discussion"
with a colleague about the best way to
implement the data layer in a new
application.
One viewpoint is that the data layer
should be aware of business objects
(our own classes that represent an
entity), and be able to work with that
object natively.
The opposing viewpoint is that the
data layer should be object-agnostic,
and purely handle simple data types
(strings, bools, dates, etc.)
There is no problem with passing dataset across layers. If you observe, you will notice that passing dataset is by reference and not by value.So there is no issue of performance here.
Now what you read is also right, but you have to understand the context. If you are passing the dataset across remote boundaries, that is not a recommended practice.
There's nothing fundamentally wrong with that doing that. Although the basic idea of having a DAL, BLL and UI layer is so that each layer can abstract what's beneath it. E.g. the BLL shouldn't have any knowledge of how the database is structured because the DAL abstracts that away. If a dataset is being loaded in the DAL then passed straight through the BLL to the pages, it kind of sounds like the BLL is pointless.
The strongest statements often seen about DataSet is not to pass it into or out of a web service. That goes beyond exposing implementation details, and includes exposing details of the platform (.NET).
Although it's possible to change "table" and "column" names in a DataSet from those in the underlying database, you're still largely stuck with the underlying structure of the database. To abstract that, I would use Entity Framework. It allows you, for instance, to define a "Customer" entity which takes data from multiple tables and puts it into a single entity. Code using the entity doesn't need to know whether it is implemented as one table, two tables, or whatever.
Even there, you should not pass these entities outside of a web service boundary. They still pass implementation details outside of the implementation. For instance, properties of the base classes get serialized, even though these are just implementation details.
As far as I've understood, the DataSet requires the db connection to be open, for as long as it is used, which will reduce performance in your application as it keeps the connection open until the content is rendered.
Instead, I recommend using generic collections, such as IEnumerable<myType> or IQueryable<myType>, where myType is a custom type which you fill with your data.
I'm thinking through data access for an ASP.NET application. Coming from a company that uses a lot of Windows applications with Client Data sets there is a natural dendancy towards a DataSet approach for dealing with data.
I'm more keen on a Business Object approach and I don't like the idea of caching a DataSet in the session then applying an update.
Does anyone have any experience / help to pass on about the pros and cons of both approaches?
You are smart to be thinking of designing a Data Layer in your app. In an ASP.NET application this will help you standardize and pretty dramatically simplify your data access. You will need to learn how to create and use ObjectDataSources but this is quite straightforward.
The other advantage of a data access layer (built using a separate project/DLL) is that it makes Unit testing much simpler. I'd also encourage you to build a Business Layer to do much of the processing of data (the business layer, for example, would be responsible for pulling ObjectDataSources from the DAL to hand to the UI code). Not only does this let you encapsulate your business logic, it improves the testability of the code as well.
You do not want to be caching DataSets (or DAL objects, for that matter) in the session! You will build a Web app so that record modifications work through a Unique ID (or other primary key spec) and feed changes directly to the DAL as they are made. If you were to cache everything you would dramatically reduce the scalability of your app.
Update: Others on this thread are promoting the idea of using ORMs. I would be careful about adopting a full-blown ORM for reasons that I have previously outlined here and here. I do agree, though, that it would be wise to avoid DataSets. In my own work, I make extensive use of DataReaders to fill my ObjectDataSources (which is trivial due to the design of my DAL) and find it to be very efficient.
DataSets can be incredibly inefficient compared even to other ADO.NET objects like DataReaders. I would suggest going towards the BO/ORM route based off what you are saying.
If you're going to follow Microsoft's direction, then the trend is definitely towards LINQ (ORM) vs. DataSets. When DataSets came into being (ASP.NET 1.0), LINQ wasn't even possible. With LINQ you get type-safety and build-in functions to Create / Update / Delete from the database.
Microsoft has even tried to make the transition easier through LINQ to DataSet.
We're about to do a big update to an existing asp app that used DataSet objects heavily; although I am not looking forward to the pain, I am going to insist on going down the BO route. Just the thought of trying to make datasets work now causes me to break out in a sweat.
I think we are going to go down the LINQ route and use lightweight entity objects.
The company where I work makes heavy use of DataSets as well while there is a business layer as well. BL mainly loads datasets from the DB.
I personally dislike this approach. There is also a practice of direct modifying the datasets after load/before save to meet some immediate needs here and there. To me it really violates the idea of business objects but it's how it is done.
ORM frameworks can really save you a great deal of time, especially in enterprise applications with lots of views with similar buttons and operations.
But it's also easy to lose control. Since that point it will slowly be turning into a mess.
Both options are good when used in right cases. Just don't mix them. Decide to do it one way and follow it.
Mark Brittingham's answer is accurate for two tier applications. But what if I want to use a service tier. DataSets are serializable. Typed DataSets save time over hand coding your own objects. Typed DataSets are extendable. Linq to Entities has performace issues, Linq to SQL is now dead. Linq to DataSet will always be an option.
I will use Typed DataSets and a multi-layered architecture to save time and organize code. I've tried hand coded BOs and the extra time and maintenance time is not worth it.