Visualizing Data Models

225Chapter 14 Visualizing Data Models After completing this chapter, you will be able to: ■ ■ Design an entity model using drag-and-drop techniques ■ ■ Describe how Visual Studio convert

225

Chapter 14

Visualizing Data Models

After completing this chapter, you will be able to:

■

■ Design an entity model using drag-and-drop techniques

■

■ Describe how Visual Studio converts Entity Framework models to source code

■

■ Import objects from an existing database into the Entity Framework

ADO.NET’s Entity Framework (EF) rests on a foundation of XML schema files From the con-ceptual model used in your applications to the mapping links between your code and an external database, EF stores its core modeling data using three different XML schema languages

If you already understand XML, using these schema variants is not overwhelming But trying

to handcraft three layers of modeling data for the dozens or even hundreds of database ob-jects that support a complex enterprise application is a considerable undertaking

Fortunately, Visual Studio includes the ADO.NET Entity Data Model Designer, a visual design

tool that makes model design as simple as adding controls to a Windows Forms application This chapter shows you how to use the Designer and its various design elements Whether you are importing an existing database schema into an application or creating custom enti-ties for an application’s internal use, the Entity Data Model Designer will help you move from the model design phase to actual software development quickly and easily

Designing an Entity Framework Model

Given the complexity of the Entity Framework, the Entity Data Model Designer included with Visual Studio is surprisingly simple All you need to use it is an existing Visual Studio project

Using the Entity Data Model Wizard

You can build a model using the Entity Data Model Designer starting from a blank slate, let-ting you model new entities as needed within your application For many projects, though, you’ll create the base model from the logical objects stored in an existing database When you add a new Entity Data Model (EDM) to your project, Visual Studio prompts you to import tables, stored procedures, and other objects from an existing database using the

ADO.NET Entity Data Model Wizard.

Note The wizard’s capability to build a model from an existing database can be limited by se-curity rights and restrictions imposed on your database account Make sure you have sufficient rights to the database tables and elements that you will model in your application.

Similar to the Data Source Configuration Wizard demonstrated in Chapter 1, “Introducing ADO.NET 4,” the Entity Data Model Wizard guides you through the database selection and connection process, which serves four main purposes:

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■ To build the connection string for both the model and the target database Built

upon standard ADO.NET connection strings, this wizard adds EF-specific metadata key-value pairs that help the Framework access the three XML-based modeling layers

metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;

provider=System.Data.SqlClient;

provider connection string='Data Source=(local)\SQLExpress;

Initial Catalog=StepSample;Integrated Security=True;

Connect Timeout=30;User Instance=True'

In this sample, the expected SQL Server connection string comes after three resource references that identify the Conceptual Schema Definition Language (CSDL), Store Schema Definition Language (SSDL), and Mapping Specification Language (MSL) mod-eling documents

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■ To build an application-side storage layer that parallels the database-side tables, views, and stored procedures specified in the wizard This layer appears within

your application using the SSDL schema language, a layer that is only indirectly acces-sible through the model designer

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■ To create a conceptual model of the imported storage items At first, this model

will be nearly identical to the logical organization of the storage layer You will have the opportunity to adjust this model to meet the needs of your application This layer

is created using the CSDL schema and is presented in the visual designer as a series of database modeling objects on a design surface

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■ To link the storage and conceptual models with mappings using the MSL schema language An additional Visual Studio panel called the Mapping Details panel lets

you modify the mapping relationships for all entities and associations included in the conceptual model

That’s a lot of activity Fortunately, the wizard performs most of it through a few point-and-click actions

Importing Database Tables as Entities

1 Create a new Windows Forms application (or almost any standard Visual Studio

applica-tion) using either C# or Visual Basic

2 In the Visual Studio development environment, select the Project | Add New Item menu

command When the Add New Item dialog box appears, select ADO.NET Entity Data

Model from the list of template items Change the default item name to SalesOrder.

edmx Click Add.

3 The Entity Data Model Wizard appears On the Choose Model Contents panel, select

Generate From Database; then click Next

4 On the Choose Your Data Connection panel, either select an existing connection to

the book’s sample database from the drop-down list of connections or click New Connection to locate the sample database

Note The Visual Studio 2010 Entity Framework tools do not support SQL Server 2000 or earlier When importing objects from a SQL Server database, you must use SQL Server 2005 or higher.

The EF-modified connection string appears in the middle of the panel If you use SQL Server security with a plain-text password, the wizard will ask you to indicate whether

to store this unsecured connection string For this example, select Yes if prompted The Save Entity Connection Settings In App.Config As option near the bottom of the panel

should already be selected Under this field, enter SalesOrderEntities as the

configura-tion name Click Next

5 The Choose Your Database Objects panel appears.

In this hierarchical list of objects, select the Customer and OrderEntry tables, plus the CancelOrder stored procedure The Include Foreign Key Columns In The Model field is

already selected, which in this case will add the OrderEntry.Customer database field as a

distinct conceptual property Maintaining this setting also limits your ability to modify

the mapping details between the two tables Clear this field Enter SalesOrderModel as

the Model Namespace Click Finish to close the wizard and generate the model

Note Imported views and table-valued stored procedures are read-only in the model You can modify the model to add support for updates if you provide the relevant SQL commands or

stored procedures yourself.

6 The model appears in the main Visual Studio window as SalesOrder.edmx The design

surface includes distinct Customer and OrderEntry entities that are connected by a line.

Entity Data Model Designer

The design surface of the Entity Data Model Designer hosts visual representations of enti-ties and associations If you have worked with other third-party entity-relationship modeling tools, the presentation should be familiar Each entity appears as a collapsible rectangle with the name of the entity in bold at the top Below the name is a list of defined entity proper-ties, followed by any navigation properties

Entity Name

Properties

Navigation Properties

Associations appear as lines connecting related entities Although the line does not indicate which properties are joined by the association, the cardinality (that is, the multiplicity of the association endpoints) does appear as indicators on either end of the line

The bottom-right corner of the Designer includes four display controls that let you adjust the view of the model From top to bottom, the four controls are: Zoom In, Zoom To 100%,

Zoom Out, and Move Via A Thumbnail View Right-click on the design surface to see addi-tional view management options through a shortcut menu

Zoom In

Zoom to 100%

Zoom Out

Move Via a Thumbnail View

The Designer’s main purpose is to simplify the creation and editing of entities and their asso-ciations You perform most of these editing activities by clicking entities, entity properties, or associations You then use the Visual Studio Properties panel to modify the various settings

of the selected entity, property, or association Right-clicking entities, properties, associations,

or even on the design surface provides access to additional editing and model management features

A full listing of editing activities is available in the Visual Studio online help The following list shows some the main tasks you can accomplish using the Model Designer:

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■ Edit entities To add a new entity, right-click the design surface and select Add | Entity

from the shortcut menu The Add Entity dialog box that appears lets you specify the new entity name, its primary key (if any), and any inheritance relationship it has to an existing entity

On the design surface, select an existing entity and use the Visual Studio Properties panel to manage its basic settings To remove an entity, click that entity in the Designer and press Delete

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■ Edit properties To create a new property within an entity, right-click the entity and

select one of the Add | Property choices from the shortcut menu The Designer supports three types of properties: scalar properties, which are simple types such as strings and numbers; navigation properties, which enable natural links between different entities; and complex properties, a grouping of other simple types based on some conceptual

relationship Complex types—such as an Address type that contains distinct street, city,

and postal code properties—can be defined independently by right-clicking the design surface and selecting the Add | Complex Type shortcut command

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■ Edit associations Add a new association by right-clicking an entity and choosing

Add | Association from the shortcut menu The Add Association dialog box that appears lets you define the endpoints of the association, including the multiplicity of each end

Select an association and use the Visual Studio Properties panel to manage its settings (Most of the settings are unavailable if the association is based on a storage layer for-eign key relationship.) To remove an association, click its line in the Designer and press Delete

■ Refactor complex types The Designer can craft a new complex property (and its

underlying complex type) from an entity’s existing properties To create such a complex property, select all involved properties within the visual entity Right-click the selected group and choose Refactor Into New Complex Type from the shortcut menu

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■ Edit function imports Function imports are database-level stored procedures as

expressed through an entity container Once defined, calling a stored procedure is as simple as making a normal class-based method call The Add Function Import dialog box, available through the Designer’s Add | Function Import shortcut command, lets you locate and define these new function calls

The dialog box can auto-detect the procedure’s return type, although you might need

to make slight adjustments Having an accurate return type allows you to use a defined function with the different editing operations of an entity or entity component

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■ Auto-update the model If the underlying database objects change in a way that

af-fects the model, you can refresh the model by using the Update Model From Database shortcut command through a right-click on the design surface

Each time you save changes to your model (or allow it to be auto-saved as configured through your Visual Studio preferences), Visual Studio regenerates the Visual Basic or C#

source code object layer representation of the model To view this code, open the

<model-name>.Designer.cs or <modelname>.Designer.vb file from the Solution Explorer panel.

Note Visual Basic hides this file by default To access the file, click the Show All Files toolbar but-ton within the Solution Explorer panel.

Any changes you make within this designer file will be lost the next time Visual Studio

gener-ates the model’s object layer You should not make changes directly to this file! However,

be-cause the generated code consists of standard NET classes, you can add a partial class file to your project or use other language-specific or Entity Framework–specific features to enhance the generated content

Note Visual Studio uses the “default code generator” when building a model’s object layer You can override this default, and even write your own object layer generation rules, by adjusting some of the default model settings See the “Managing the Object Layer” section on page 241 of this chapter for information on controlling the code generation process.

Changes made to the model do not propagate back to the underlying database The purpose

of the model is to provide a meaningful conceptual view of the data to your application, a view that does not need to exactly match the logical structure of the database

Creating a Complex Property from Scalar Properties

Note This exercise continues the previous exercise in this chapter.

1 In the Customer entity on the Entity Data Model Designer’s design surface, use the

mouse along with the Shift or Control keys to select all the following properties at the

same time: Address1, Address2, City, StateRegion, and PostalCode.

2 Right-click the group and then select Refactor Into New Complex Type from the

short-cut menu

The Designer will replace the previously selected properties with a single property

named ComplexProperty.

3 Right-click the ComplexProperty property and then choose Rename from the shortcut

menu Change the name of the property to Address.

4 Save changes to the model or the project to regenerate the object layer.

Working with the Mapping Details Panel

The focus of the Designer’s visual design surface is on the conceptual model, the CSDL con-tent as expressed through a convenient Visual Studio editor The Entity Framework design

tools also include a Mapping Details panel that lets you modify the mapping layer (the MSL

content) as it relates to the conceptual model

Note Although you can build a storage layer manually using the SSDL schema language, and al-though the Entity Data Model Wizard generates SSDL content based on an external data source, the Entity Data Model Designer does not include features that let you directly modify the storage layer.

If not already available in your Visual Studio Integrated Development Environment (IDE), access the Mapping Details panel by right-clicking the model’s visual design surface and selecting Mapping Details from the shortcut menu

To use the Mapping Details panel, select an entity from the visual design surface The panel displays all column mappings already defined for the entity, with storage model properties

on the left half and conceptual model properties to their right To modify the conceptual

property for a storage model property, click in the Value / Property column to the right of

the storage model property name and use its drop-down list to select a different conceptual model property