MSDN Magazine - July 2008 - (Page 26)

to the conceptual entity model (the Entity Data Model, or EDM), map the entity aspects to the storage layer, and generate a SQL query to execute against the database. var q = from c in context.Customers select c; List customerList = q.ToList(); Now that I’ve provided a high-level overview of how the layers work in the architecture, let’s examine the key aspects of each layer as they pertain to the Entity Framework. Since the database already exists for the application, I generated the entity model from the NorthwindEF database as a starting point. I could have built the entity model first and How It Works then mapped the entities to the database as well. Now I will demonstrate the application The EDM wizard helps generate the base entity and discuss how it operates from the top layer model, which can then be modified as needed down, starting with the views (located in the to incorporate inheritance, entity splitting, and Figure 2 Generating the Model NWUI project) and the presenters (located in other domain modeling concepts. Figure 2 from the Database the NWPresentation project). Both projects are shows the EDM wizard with all tables and available in the code download that accomstored procedures selected to be imported panies this column. The application loads a into the EDM. customer search view, which allows the user One topic that often causes people confuto search for customers by matching the sion in regard to EDMs is the default naming company name criteria (see Figure 4). The convention for the EntitySets and the Entityview is implemented using WPF, and when Types. I like to use singular names for all of a user interacts with the view it raises events my entities in my domain models. I create that are listened to by its presenter, who can an instance of a Customer or return a list of then take appropriate action. Order instances using List . Each enWhen the user searches for all customers tity is a singular instance of a blueprint that Figure 3 Changing the EntityType Names starting with the letter D, as shown in Figure has properties defining the entity. 4, the view raises an event when the user clicks On the other hand, I like my EntitySets to use a plural naming the Search button. The presenter listens for this event and responds convention. The EntitySets are often used in LINQ queries when ask- by calling the service layer through WCF to get the list of customer ing the ObjectContext to refer to its set of Customers or Orders. entities that will be displayed on the CustomerSearchView. Here is As an example of this, take a look at the following LINQ to En- the code in the view when the user clicks the Search button: private void btnSearch_Click(object sender, tities query: var q = from c in context.Customers select c; List customerList = q.ToList(); { RoutedEventArgs e) Building the Model When the EDM wizard generates the model, the EntitySet and EntityType names can easily be modified. This can be done by selecting the entity in the diagram, viewing its properties in the Properties window, and modifying the desired setting (see Figure 3). For this application, I modified all of the EntityTypes to be singular by setting the Name property. I did not change the EntitySet Name property, since it was already plural. This query tells LINQ to Entities to access the Customers EntitySet } and return all Customer entity instances when executed. The secThis code does not interact with the list of entities that are reond line executes the query and returns the turned, but, rather, it leaves that up to the List to the local variable named presenter. The view uses WPF data bindcustomerList. The EntitySet is plural in this ing to reference the entity’s properties so it example, making it clear that it is querying knows how to bind the list of entities to the EntitySets and returning instances of the list view control’s elements. The only interCustomer (notice this is singular) entity. action the views have with the entities is Is it necessary to have this naming conventhrough the data binding. tion? Of course not. However, I find it helps The CustomerSearchView raises the make my code more readable. Otherwise, event FindCustomerSearchResults, and the if you take the default of what is returned CustomerSearchPresenter listens for the from the EDM wizard, you get an Entityevent and responds by taking the baton and Sets named Customers and an EntityType performing the search. The following code named Customers, which makes your LINQ shows how the CustomerSearchPresenter to Entities query look like this: Figure 4 Searching for Customers class creates an instance of the NWService26 msdn magazine Data Points if (FindCustomerSearchResults != null) FindCustomerSearchResults();

Table of Contents Feed for the Digital Edition of MSDN Magazine - July 2008

MSDN Magazine - July 2008 Contents Toolbox CLR Inside Out Flex Your Data Data Points Advanced Basics Office Space Cutting Edge Data Services ADO.NET Data and WPF Transactions WCF P2P Test Run Security Briefs Foundations .NET Matters {End Bracket}

MSDN Magazine - July 2008

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