ASP.NET 4.0 and the Entity Framework 4 - Part 4 - A 3 Layered Approach to the Entity Framework
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Published: 04 May 2010
Abstract
In this article, Vince suggests a pattern to use when developing a three layered application using the Entity Framework 4. After providing a short introduction he demonstrates the creation of the database, data access layer, business logic layer, and a web form. He does so with the help of detailed explanations, source code examples and related screenshots. He also examines how to select records to load a Drop Down List, including adding, editing and deleting records.
by Vince Varallo
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Introduction

The previous 3 articles in this series showed you how easy it is to use the Entity Framework 4 to create a database, add, update, delete, and select records from tables, and also how to execute stored procedures.  The actual amount of coding required to create a web page that can manage data in a table is quite small.  However, the examples didn't really show you any type of pattern.  They simply showed you the syntax for making the web page work.  I'm sure by now you've read an article or a book about separating your logic into the user interface, the business logic layer, and the data access layer and are scratching your head thinking that the Entity Framework kind of encapsulates the business layer and data access layer and all you need is a GridView control on your form and you're in business.  For some applications this can and will work fine.  Every pattern isn't for every application or every developer.  However, just from experience I have always found it better to at least separate out the three layers logically. 

This article will create the same web page that was created in the second and third articles except it will introduce a pattern for developing the application as a three layered application.  Notice that I didn't say three tiered application. A tier really means a logical and physical separation of the layers. A layer implies just a logical separation. For many applications that's all you need.  I'm not one to advocate over-engineering a system. I always follow the simpler, better approach as long as the developers working with you understand the pattern. 

This article will create a web application as the user interface layer and two class libraries for the business logic layer (BLL) and the data access layer (DAL). The code to communicate with the database will be encapsulated in the DAL project. The entities in the Data Context will act as the data transfer objects (DTOs) that pass data between the DAL and BLL. The concept of a DTO is not new. Previously you would need to write your own custom classes but the entity framework can save you all that custom coding.

The goal of this article is to create a web page that allows a user to maintain the records in a table called UserAccounts. The final web page looks like the following image.

The drop down list at the top of the page allows you to navigate from user to user and displays the properties on the page.  The user can simply click the Save button to add or update records or click the Delete button to remove a record.


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User Comments

Title: Where is the UserAccounts table diagram?   
Name: Fernando Linhares
Date: 2012-07-11 6:12:05 PM
Comment:
Hello,
Thanks for the article series.
Where is the UserAccounts table diagram picture?
Thanks,
Fernando
Title: without stored procedures   
Name: Junior
Date: 2012-06-06 2:21:42 PM
Comment:
how would this approach without stored procedures ?
Title: problem   
Name: zia
Date: 2012-05-22 9:33:03 AM
Comment:
Brother i cant see the pictures u given in the project
Title: Mr   
Name: Varun Maggo
Date: 2011-03-16 4:16:28 AM
Comment:
You rockmaan!
Title: Nice work!   
Name: janmeis
Date: 2011-03-02 11:52:40 AM
Comment:
Thanks Vince, I've created the project according the article and it works fine! There's one minor bug, the SCOPEIDENTITY returned by the UserAccounts_Insert procedure is mapped as decimal not int, so in the item 16 the procedure must be as follows "...you need to change the "Returns a Collection Of" to Scalars and choose decimal from the list." Then it can be casted to int in the "public static int Insert". Link with the uploaded project is attached.
Title: connectionstring problem   
Name: Mark
Date: 2010-12-25 7:59:09 AM
Comment:
I am getting server error on data source keyword.

Keyword not supported: 'data source'.

Exception Details: System.ArgumentException: Keyword not supported: 'data source'.
Title: Lnking to a data Object   
Name: Richard
Date: 2010-10-01 4:12:41 PM
Comment:
So far so good, but now I have this BLL how do I use it say in a datagrid?
Title: Where is the concurrency management???   
Name: Matt
Date: 2010-07-30 12:52:28 PM
Comment:
Where is the concurrency management code? If you load a user account from the database and five minutes later the person clicks the submit button how do you handle the issue where someone else already updated that record and you need to check for that???
Title: Why add the DAL and BLL as separate projects?   
Name: Alan
Date: 2010-07-12 12:16:59 PM
Comment:
Even assuming that this is a good way to structure your application (which seems to be a matter of debate judging by other people's comments), why did you do the DAL and BLL as separate projects? I don't see any benefit at all to this.

Given that this is a web site, why not just add the .cs files for the DAL and BLL to the App_Code folder? You would then have the objects you need to separate the layers, but you wouldn't have the extra mess of separate projects and DLLs.
Title: Not convincing   
Name: Kum
Date: 2010-05-09 11:27:07 AM
Comment:
Duplicate data model, one generated by entity framework in DL and another hand written in BL...
There should be a better way.
Title: Is it realy the way?   
Name: Kristian
Date: 2010-05-07 6:54:23 AM
Comment:
Though I loved article part 1 and 2, this seems like a bad approach, like Mant wrote. Why do another mapping?
Title: Good Work   
Name: Rajbharat
Date: 2010-05-07 6:40:38 AM
Comment:
Its good and simple to follow..thanks for ur good work
Title: Appreciate that!   
Name: Waldek
Date: 2010-05-06 5:57:10 AM
Comment:
Thanks a lot Vince! Based on your articles all kinds of web.CRUD applications can now be built with a little hassle!
Title: use IsNullOrWhiteSpace instead if .Trim() == ""   
Name: Binoj Antony
Date: 2010-05-06 5:14:00 AM
Comment:
Suggest that you improvise FirstName.Trim() == "" with
string.IsNullOrWhiteSpace(FirstName).

Also the most of the else blocks that does just a return false , here you could eliminate the else and just write return false; (This last one is just an opinion)
Title: Bad Approach   
Name: Mant
Date: 2010-05-05 11:05:10 AM
Comment:
It seems what you have done is take the approach used in 1.1/2.0 with datasets then just swapped them with the Entity Framework completely missing the point of an ORM. I would suggest reading up on the Repository pattern, Unit of Work pattern, specification pattern and persistence ignorance. There are some great examples of using the framework out there, but just about everything in this one is a poor way of doing things.
Title: Great article!   
Name: Rich D.
Date: 2010-05-05 9:13:07 AM
Comment:
I loved the article. I was looking for some direction and ideas on how to create a BL. But, I thought the idea was to save much of the template hand coding by using t4 templates to generate POCO classes for the BL. The template for self-tracking entities looks promising for n-tier architectures.
Title: ASP.NET 4.0 and the Entity Framework 4 - Part 4 - A 3 Layered Approach to the Entity Framework   
Name: Ray
Date: 2010-05-05 3:16:16 AM
Comment:
Thanks Vince for a very helpful article.......
Title: ASP.NET 4.0 and the Entity Framework 4 - Part 4 - A 3 Layered Approach to the Entity Framework   
Name: tvs
Date: 2010-05-04 9:35:39 PM
Comment:
a very good article... well done vince...

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