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GETTING STARTED WITH ENTITY FRAMEWORK
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Figure 1-5. Key parts of a model in the designer Of course, there is a lot more to the designer and the model than just the few key parts illustrated in Figure 1-5. In the recipes in this book, we ll cover just about every aspect of using the designer to create models. In some cases, we go beyond what can be done with the designer and show you how to create models that require directly editing the underlying .edmx file. The .edmx file contains the complete model definition, including the conceptual layer, store layer, and mapping layer. Okay, now that you have a model, how do you program against it Well, that s where Entity Framework really shines: you program against objects in the model (EntityTypes) as you do with other objects in your application. For the model in Figure 1-5, your code uses Customer and Order in much the same way as you use other objects. If you want to insert a new customer and order into the database, you can use the new operator to create instances of the Customer and Order types, set the properties, add them to the in-memory context that represents the model, and call SaveChanges(). All the necessary SQL code is generated and sent to the database to insert the rows. To retrieve customers and orders from the database, you use either LINQ or Entity SQL to create a query in terms of the EntityTypes and associations in the model. The recipes throughout this book will show you step by step how to model just about every conceivable database scenario; how to query, insert, update, and delete using these models; and how to use Entity Framework in many kinds of applications.
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Entity Data Modeling Fundamentals
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Entity Framework is a new technology from Microsoft. More likely than not, you are just beginning to explore Entity Framework and you are probably asking the question, Okay, how do I get started If this describes you, this chapter is a great place to start. If, on the other hand, you have built some working models and feel comfortable with a few key modeling concepts such as entity splitting and inheritance, you can skip this chapter. In this chapter, we will walk you through the basic examples of modeling with Entity Framework. Modeling is the core feature of Entity Framework and what distinguishes Entity Framework from previous Microsoft data access platforms. Once you have built your model, you can write code against the model rather than against the rows and columns in the relational database. We start off this chapter with an example of how to create a simple conceptual model and let Entity Framework create the underlying database. In the remaining examples, we will show you how to create models from existing tables and relationships in your databases.
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2-1. Creating a Simple Model
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You have a brand new project and want to create a model with just one entity.
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Let s imagine you want to create an application to hold names and phone numbers of people you know. To keep things simple, let s assume you need just one entity type: Person. To create the new model, do the following: 1. 2. 3. 4. Right-click your project and select Add New Item.
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From the templates, select ADO.NET Entity Data Model and click Add. This template is located in Data under Visual C# Items. See Figure 2-1. In the first step of the wizard, choose Empty Model and click Finish. The wizard will create a new conceptual model with an empty design surface. Right-click the design surface and select Add Entity.
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ENTITY DATA MODELING FUNDAMENTALS
Type Person in the Entity name field and select the box to Create a key property. Use Id as the Key Property. Make sure its Property Type is Int32. Click OK, and a new Person entity will appear on the design surface. See Figure 2-2. Right-click near the top of the Person entity and select Add A new scalar property will be added to the Person entity. Scalar Property.
6. 7. 8.
Rename the scalar property FirstName. Add scalar properties for LastName, MiddleName, and PhoneNumber. Right-click the Id property and select Properties. In the properties view, change the StoreGeneratedPattern property to Identity. This flags the Id property as a value that will be computed by the store layer (database). The database script we get at the end will flag the Id column as an identity column, and the storage model will know that the database will automatically manage the values in this column.
The completed conceptual model should look like the model in Figure 2-3.
Figure 2-1. Adding a new .emdx file that contains XML describing the conceptual model, storage model, and mapping layer
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