If I use ADO.NET Entity Framework in our project and we depend on a 3-layer architecture pattern that we have ( presentation layer - business layer - data access layer ) a project for each layer.
So when I make an entity model file where can I put it in the DAL or BL? If I put it in the DAL and from the presentation layer want to access a domain object in it through the business layer so we need to add a reference to the DAL in the presentation layer. Also, how do I get that type of an object as it is created in the DAL? On the other hand should I put the entity model file in the business layer? Which is the better and why?
Ideally, the EntityFramework generated code makes up your data layer. You would basically have some repetition then in your business layer if you needed the same sorts of objects in your business layer as you have in your data layer. Unfortunately, EntityFramework doesn't really help you at all with your business layer.
Now, you'll also read things about EntityFramework that say you can/should use it as a combined data/business layer. That violates Separation of Concerns, so I would guide you away from it, but I'm sure a ton of people do it anyway. If you wanted to move from EntityFramework to NHibernate some day, you'd be best off trying to isolate your ORM from the rest of your code base and minimize any coupling to the ORM (often through implementing something like a Repository pattern).
People who talk the language of MVC will often use EntityFramework as the Model and may or may not distinguish between a data layer and a business layer (which generally would both live in the Model). Even if you use MVC, I still believe you should decouple your data access from your business rules and business logic.
You can place the entities in a separate class library project, for example: Common Entity Library. This library can be referenced in any other app layers. You can then work with collections across application domain.
As I see it the Entity Framework is your DAL. It provides the needed tools to abstract the Model objects exposed by the Entity Framework from the persistance services of a backend database.
The Entity Framework straddles both the Business Layer and the DAL from this old three layer pattern. My advice is if you going with the Entity Framework is stop thinking in terms of Presentation->Business->Data and think more in terms of View->Model.
Related
I have an n-tier application design problem with Entity Framework 4.
Server-side, my application has 3 layers :
- one Service layer (WCF)
- one Business layer
- one DataAccess layer (working with EF4)
The Entities are POCO, place in a independent project/assembly.
I'm using Dependency Injection for creating objects of the business and the DataAccess layers, therefore i only work with interfaces, and I have no dependency to EF in my business layer.
I'd like to use EF Compiled Queries to improve performances.
But my (business) queries are defined in the business layer, since in my architecture, the DataAccess is only providing the CRUD methods.
So the compiled queries should be defined in business layer, but i have no dependency to EF and don't want one to keep loose coupling, hence, i can't call the ObjectContext from there.
And defining the queries in DataAccess does not fit my application design.
So does anyone know if there is a generic way to inject the business queries from the business layer to the DataAccess layer, so that i can use them with Compiled queries ?
I've tried many things and looked everywhere, and couldn't find an answer to this ... :( looks like EF does not fit well with that kind of n-tier application.
Compiled query belongs to data access layer because it is data access specific feature dependent on data access classes. If your design doesn't accept this it is simply not ready for data access specific features = either change your design or don't use data access specific features.
The simplest way is to add compliled queries to your context and expose them as methods on the context:
public IQueryable<SomeEntity> SomeQuery(string someParam) {
return compiledQuery.Invoke(this, someParam);
}
Now you will add these methods to the interface for the context.
You can follow similar approach and expose compiled query on any data access interface visible in business layer.
I'm developping a line of business application using WPF as a presentation layer (of course with MVVM).
I'm using ADO.Net Entity Framework to map the DataBase.
I don't want to use entities directly in code (in the business layer). I want to separate my project into 3 layers:
Presentation layer
Business Layer
Data Access Layer
According to this post I want to implement a full encapsulation of the Entity Framework to provide a separation of concerns and to not be dependant on EF as ORM in the future.
Can you help me by giving me some exemples to encapsulate the EF and how to implement this in code.
Regarding this
I want to implement a Full encapsulation of the Entity Framework. to
provide a separation of concerns and to not be dependant on EF in the
future as ORM
Normally, you will create yourself a lot of problems if you go that route. If you choose EF, you really should make full use of the features, not hiding that behind another abstraction.
EF itself is already an abstraction layer over DB, there is no need to create another abstraction on top of that.
I would take a look at this post wich implements UnitOfWork and Repository patterns to implement what, I understand, you want to achieve.
http://blogs.msdn.com/b/adonet/archive/2009/06/16/using-repository-and-unit-of-work-patterns-with-entity-framework-4-0.aspx
There is one way of doing it, using POCO. Entity Framework 4.0 comes with the support of POCO (Plain CLR Objects). But POCO has its own complexities, when u have to deal with Relationship and associations. You can refer to the blog by Julie Lerman (a nice article)
http://thedatafarm.com/blog/data-access/agile-entity-framework-4-repository-part-1-model-and-poco-classes/
im doing some self-study on architecture of a MVVM-light - EF Application
im trying to build a product/Receipt like app.
I have a Db/EF with a Product and Receipt Table/Entity in a many to many relation.
then i have a DAL wich simply uses Linq to do simple CRUD.
the question is where and how to put my business logic in this app.
a couple of ideas came to mind
option 1
-make a ReceiptBo (Receipt business object)
wich inherit the Entity Receipt class and Icollection(ProductBo)
the ReceiptBo class would be responsible for adding Product,calculating total and subtotal and calling the Dal for inserting.
maby this option seemed a little overkill.
option 2
-put the calculating methods in the generated Entity objects by using partial classes
and simply using the BuisnessLayer to call the Dal.
this would make the Buisnesslayer Classes obsolete in my opinion and im not sure that Entity classes should be used for Business logic at all ?
option 3
-make the Business Classes but dont bother using inheritance, just add products to the Entity's and do the calculations there and call the Dal for insert.
wich seems simple but not very elegant.
option 4
-none of the above and im clueless
right now im not using WCF but the idea is that i want to make this app loosly coupled so that it would be easy to implement it and further extend it.
also im a little confused about what an Business layer is. in some examples it is more used like a Dal that also does the computing, then others say this is not done.
some help would be great. thx
ps: sorry for my bad english
Really, I would go simple here and choose a common multi-tier architecture designed as follows:
a data access layer (basically, your Entity Framework model along with all your entities)
a business layer that exposes methods to access to your entities (CRUD methods + any custom method that run some logic)
a service layer that exposes stateless methods through WCF (service+data contract)
the presentation layer (in your case using MVVM pattern)
Views (XAML pages)
ViewModels (C# classes)
Model is represented here by the entities that are exposed through WCF by the service layer
I wouldn't add any method directly in the entities. All methods are defined in the business layer, and exposed by the service layer.
Usually I keep my business logic in my ViewModels, not my Models, and I view EF objects as Models. At most, they'll have some basic data validation, such as verifying length or required fields.
For example, an EditRecieptViewModel would validate business rules such as verifying values are in a specific range, or verifying that users have access to edit the object, or performing some custom calculations when a value changes.
Also, don't forget that ViewModels should reflect the View, not a Model, so not every Model will have a ViewModel of its own
In MVVM, can the model bit be a Domain Model, or can it also be classes generated by Linq2SQL or EF?
Yes and no! The business layer & data layer of your application would consititute the MODEL as far as the MVVM pattern goes.
If your app is anything other than short lived and simple I would implement the MVVM model bit as two distinct layers; a business layer with the domain model and its corresponding data access layer.
As a big fan of DDD (domain Driven Design) I would advocate a domain model that is as close to POCO (Plain old CLR Objects) as you can manage. Use the Repository pattern to isolate those classes (which should effectivly be nothing but the application's business logic) from the nuts and bolts of data access. In the data access layer plonk all the EF or LINQ-to-SQL code.
Data acess code in a data access layer, business logic in its own layer. The two are different and deserve their own focused application layers IMHO.
If I understand MVVM correctly, the point of the pattern is that the ViewModel acts as a presenter between the Model and the View; it takes in a Model, and puts it / adapts it to a form that is understandable by a View. So in that frame, your model could be pretty much anything.
I am building an application using entity framework. I am using the T4 template to generate self tracking entities.
Currently, I am thinking of creating the entity framework code in a separate project. In this same project, I would have partial classes with additional methods for the entities.
I am thinking of creating a separate project for a service layer (WCF) with methods for the upper/presentation tier. The WCF layer will reference the entity framework project. The methods in the WCF layer will return the entities or accept the entities as the parameters.
I am thinkg of creating a third project for the presentation layer (ASP.net), this will make calls to the WCF service but will also need to reference the entities as the WCF methods take these types as the parameters/return types.
In short, i want to use the STE entities generated by the T4 template as a DTO to be used in all layers.
I was originally thinking of creating a business logic layer that maps to each entities. Example: If i have a customer class, the Business Layer would have a CustomerBLL class and then methods in the customerBLL will be used by the service layer. I was also trying to create a DTO in this business layer. I however found that this approach is very time consuming and i do not see a major benefit as it would create more maintenance work.
What is the best practice for n-tier application development using entity framework 4?
You should separate your entities and their persistence logic into separate projects. That way your Presentation layer will only need to reference the project containing the entities and be persistence ignorant.
I guess the projects breakdown as the following would be a nice approach (at least it has worked out well for me :))
Entities in one project
Persistence logic in another project (Repositories, Unit of Work
implementation)
WCF in one project
Presentation layer
Hope it helps.