Microsoft ADO .NET 4 Step by Step - p 27 potx

To use the Mapping Details panel, select an entity from the visual design surface.. The Mapping Details panel lets you link properties from multiple storage layer entities that is, from

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

The Mapping Details panel lets you link properties from multiple storage layer entities (that

is, from multiple tables, views, or table-emitting stored procedures from the target database)

to a single conceptual model entity With an entity still selected on the visual design surface, click the ghosted <Add A Table Or View> row in the Mapping Details panel

Select one of the available entities from the drop-down list After the new storage layer properties appear in the panel, modify each property as needed to define the proper data relationships

By selecting an association within the visual designer surface, the Mapping Details panel will also let you modify the mapped settings for that association

Note This ability to edit the association mapping does not apply to associations tied to

import-ed foreign key relationships.

Another useful feature of the Mapping Details panel is the ability to define conditions for mapped entities For example, you might want to limit the loaded orders for a customer to just those that have not yet been shipped By adding a condition to the OrderEntry entity

that looks for non-NULL values in the ShipDate property, the Entity Framework will

automati-cally limit the orders managed by the model’s application

Note If a storage layer property is used as a condition, it cannot be used as a standard mapped property within the conceptual model.

Adding a Mapping Condition to an Entity

Note This exercise continues the previous exercise in this chapter.

1 If you haven’t yet displayed the Mapping Details panel, open it by right-clicking the

Entity Data Model Designer’s design surface and choosing Mapping Details from the shortcut menu

2 Select the OrderEntry entity on the visual design surface The mapping details for that

entity should appear in the Mapping Details panel

3 On the column mapping for the ShipDate : date storage layer property, click the

ShipDate : DateTime value in the Value / Property column You’ll see a drop-down list of

options Select <Delete> from this list to clear the mapping

4 Near the top of the Mapping Details panel, just below the Maps To OrderEntry row,

click the ghosted <Add A Condition> item and select ShipDate from the drop-down list

5 In the Operator column of the new When ShipDate row, select Is.

6 In the Value / Property column of the When ShipDate row, select Not Null.

7 On the visual design surface, click the ShipDate property in the OrderEntry entity Press

Delete to remove the ShipDate property.

8 Save changes to the model to generate the new object layer content.

The upper-left corner of the Mapping Details panel includes two toolbar buttons

Map Entity to Tables / Views

Map Entity to Functions

The top button lets you update the mappings for an entity using the storage layer tables and other similar storage items The bottom button lets you specify database-level stored proce-dures, exposed as entity functions, that manage the insert, update, or deletion of individual entities within its entity set

Use a Stored Procedure to Manage Entity Data

Note This exercise continues the previous exercise in this chapter.

1 Select the OrderEntry entity on the visual design surface.

2 Click the Map Entity To Functions toolbar button (the lower button) on the Mapping

Details panel

3 Select the <Select Delete Function> row and then select CancelOrder from the

drop-down list

4 The Mapping Details panel detects the properties required for the selected function In

this case, a single orderID integer must be mapped to an entity value In the Property column of the CancelOrder row, choose ID : Int64 for the parameter property ID is the primary key for the OrderEntry entity.

5 Save changes to the model to generate the new object layer content.

Using the Model Browser

Visual Studio’s Model Browser panel is a hierarchical item selection panel similar to the

Solution Explorer panel When an Entity Framework visual model is active, the Model Browser displays the various components of both the conceptual and storage layers By browsing and selecting the entities, properties, and other features of a model through this panel, you can view and modify the settings of each selected item through the standard Visual Studio Properties panel

The Model Browser is an essential part of the visual model designer, because some features can be created and managed only through the browser For example, you can add, edit, and delete individual properties from an existing complex type only by accessing that complex type through the Model Browser panel

Managing the Object Layer

Visual Studio generates the source code for an entity model in your project each time you save changes to that model The generated object layer is a set of Entity Framework-aware classes that exist as standard C# or Visual Basic source code

By default, Visual Studio generates the model source code using its “default code genera-tor.” You can view this setting within the Entity Data Model Designer by selecting the design

surface of the visual model and then viewing the Code Generation Strategy property in the

Properties panel For wizard-generated models, this is set to Default.

For advanced needs, Visual Studio allows you to fully manage the code generation process

by adding a code generation item to your project These standard Visual Basic or C# language files are also known as text templates and include a tt file extension Visual Studio provides

two types of code-generation items for use with Entity Framework models:

■

■ ADO.NET EntityObject Generator This is the default type, and the same type Visual

Studio uses internally by default to generate the object layer for a model

■

■ ADO.NET Self-Tracking EntityObject Generator This advanced generator is useful

for n-tier projects in which the code that modifies EF-managed data exists in a differ-ent layer from the code that manages the structural interactions between differ-entities and model layers

To add a custom code generator to your project, use Visual Studio’s Project | Add New Item menu command, and choose either ADO.NET EntityObject Generator or ADO.NET Self-Tracking EntityObject Generator as the new item type You can also add these items by right-clicking the visual modeler design surface and selecting Add Code Generation Item from the shortcut menu

When you add a new code generation item to your project, Visual Studio makes two Entity Framework-related changes:

1 The Code Generation Strategy property for your model changes from Default to None.

2 Within the new tt file, a reference to the CSDL portion of your model appears near the

top of the code generation source code

The modification of text templates is beyond the scope of this book For details on the content of code generation items and how to modify them, search for “Generated Code Overview” within the Visual Studio online help

Summary

This chapter continued the overview of the Entity Framework by introducing the ADO.NET Entity Data Model Designer and its associated database import wizard These tools simplify one of the most common tasks performed when developing applications that use the Entity Framework: importing existing database logical objects into a new Framework model Now that you have an accessible model, you can write code that queries the data managed

by that model The next two chapters introduce two common methods of querying EF data: retrieving entity data using Entity SQL and accessing objects directly through the Entity Framework’s Object Services layer

Add a new Entity Framework model to a project Open or create a Visual Studio project.

Select Project | Add New Item.

Select ADO.NET Entity Data Model as the new item type

then click Add.

When the wizard appears, select either Generate From Database or Empty Model.

Complete the wizard steps and modify the model as needed.

Use a stored procedure to update database-side

content from entity changes

Include the stored procedure in the model, either through the initial wizard import or by using the Designer’s Add | Function Import shortcut command.

Select the entity in the visual designer.

Open the Mapping Details panel.

Click the Map Entities To Functions toolbar button (the lower button) within the panel.

In the panel’s list of functions, click the <Select Update Function> row then select the stored procedure.

If needed, assign entity properties to the stored proce-dure’s parameters.

Create a new complex type for later use in an

entity

Open the Model Browser panel.

Expand the conceptual model portion of the browser tree Right-click the Complex Types branch then select Create Complex Type from the shortcut menu.

Rename the new complex type.

Right-click the complex type to add new properties using the various Add | Property shortcut menus.

Refresh the model after making database-level

structural changes

Right-click the model’s design surface then select Update Model From Database from the shortcut menu.

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Chapter 15

Querying Data in the Framework

After completing this chapter, you will be able to:

■

■ Describe the Entity SQL language and its purpose

■

■ Create basic queries using Entity SQL

■

■ Use the Entity Provider to access data based in an entity model

The Entity Framework (EF) is a markedly different way of interacting with data traditionally found in relational databases and similar external data stores With its focus on coercing everything into NET objects, it brings a familiarity to the data management process But for those who are used to retrieving data through databases such as SQL Server and their SQL-based data query languages, moving to an object-centric paradigm doesn’t necessarily feel like an improvement

Fortunately, the Entity Framework includes a tool that helps bridge the data query gap

between SQL-based systems and Framework model-based objects: Entity SQL This query

language has all the flavor and feeling of SQL, but it runs its queries against the entities and properties of an Entity Data Model (EDM)

This chapter provides a brief overview of Entity SQL, including examples of how to use it in your code Visual Studio’s online help includes full documentation on the language If you are already comfortable with SQL, it should take you no time at all to retrieve model data us-ing this new yet familiar language

Note This chapter assumes you have some familiarity with the SQL language, especially as ex-pressed in SQL Server’s Transact-SQL (T-SQL) language.

The exercises in this chapter all use the same sample project, a tool that queries Entity

Framework data using Entity SQL Although you will be able to run the application after each exercise, the expected results for the full application might not appear until you complete all exercises in the chapter.