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NOTE The wizard also allows you to create entities for views and stored procedures.
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ENTITY FRAMEWORK
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Figure 8-4. Selecting items to generate EF classes for 11. Ensure that you have checked the Pluralize or singularize generate object names and "Include foreign key columns in the model" (these are new options in EF for more information please refer to the following Pluralization section). 12. Set the model namespace as BookModel. 13. Click Finish. EF will then generate entities for the classes we have created and you will be taken to the design view of the generated EF model (Figure 8-5).
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Figure 8-5. Design view of EF model Notice how relationships between the entities have been automatically created. This is because our database contained a number of constraints and relationships that were automatically imported into our model. You can also create relationships yourself in the design view.
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Navigating the EF model
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When your EF model contains many entities then the designer window can get pretty crowded. You can zoom in and out of the model view by clicking the magnifying icons in the corner of the scroll bars or by right-clicking and selecting the zoom level.
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Viewing How Entities Are Mapped
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If you select one of the entities, then view the Mapping Details window, you will see how the individual properties on the entity are mapped to the underlying database fields (Figure 8-6). Now select one of the individual entity properties and Visual Studio will display information in the Properties window, such as the type of field, length, and so on. Notice how you can also change the name of the field and the getter and setter properties' access levels (Figure 8-7).
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Figure 8-6. EF Mapping window
Figure 8-7. Viewing the properties of Film.Description
ENTITY FRAMEWORK
What Happens If My Database Structure Changes
When you make changes to your database then you will also need to update your EDM. To update the model simply right-click on the design surface and select Update Model from Database. Visual Studio will then bring up a dialog box allowing you to add additional tables and fields (Figure 8-8). Note that this release of EF improves the resolution of conflicts/orphaned model elements in the model browser window:
Figure 8-8. Update Model from Database
Querying Data
EF allows you to query objects in a number of different ways: LINQ to Entities (L2E) ObjectQuery methods Entity SQL
Whichever query method you use, the query gets transformed into the same query tree structure that is then processed by your model's data source provider.
LINQ to Entities
LINQ to Entities (L2E) is probably the easiest query method. L2E gives you rich query functionality and Intellisense support, and it is very easy to use. Lets write some code to iterate through our Orders and OrderItem tables displaying information about these entries.
ENTITY FRAMEWORK
1. 2.
Open Program.cs. Modify the Main() method to the following (note your entity set will, by default, be prefixed with the same name as the database in the following example, mine is Book). static void Main(string[] args) { BookEntities ctx = new BookEntities(); var query = from o in ctx.Orders select o; foreach (Order order in query) { Console.WriteLine("Order: " + order.OrderID.ToString() + " " + order.Firstname + " " + order.Lastname); order.OrderItems.Load(); foreach(OrderItem orderItem in order.OrderItems) { Console.WriteLine("Adult: " + orderItem.QtyAdult.ToString() + " Child:" + orderItem.QtyChild.ToString()); } Console.WriteLine(""); } Console.ReadKey(); }
The results are shown in Figure 8-9.
Figure 8-9. Output of LINQ to Entities query
ENTITY FRAMEWORK
ObjectQuery
You can also query EF objects with the ObjectQuery class. Let s take a look at this now. 1. Add the following using directive to Program.cs: using System.Data.Objects; 2. Replace the LINQ query with the following line of code (Note that it refers to the current entity, which in this case is Order): ObjectQuery<Order> query = ctx.Orders.OrderBy("it.OrderID");
Entity SQL
Entity SQL is similar to T-SQL (but has its own EF-specific features and intricacies); the following is an example Entity SQL query: string queryString = @"SELECT VALUE o FROM BookEntities.Orders AS o"; ObjectQuery<Order> query = new ObjectQuery<Order>(queryString, ctx, MergeOption.NoTracking); We have barely touched what Entity SQL is capable of, so for more information (on anything EF related) please refer to Julia Lerman s book Programming Entity Framework, published by O Reilly.
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