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This will start the Entity Data Model Wizard

that will help you get started building an Entity

Framework model.

This will show the dialog shown in Figure 29-2

that enables you to select whether you want to

automatically create a model from a database

(Generate from Database), or start with an empty

model (Empty Model).

The Empty Model option is useful when you want

to take the approach of creating your model from

scratch, and either mapping it manually to a given

database, or letting the Entity Framework create a

database based on your model.

However, as previously stated you will be creating an

entity model from the AdventureWorksLT database,

so for the purpose of this example use the Generate

from Database option, and get the wizard to help you

create the entity model from the database.

Moving onto the next step, you now need to

create a connection to the database (as shown

in Figure 29-3). You can find the most recent

database connection you’ve created in the

drop-down list, but if it’s not there (such as if

this is the first time you’ve created a connection

to this database) you will need to create a new

connection. To do so, click the New Connection

button and go through the standard procedure of

selecting the SQL Server instance, authentication

credentials, and finally, selecting the database.

fiGure 29-2

fiGure 29-3

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If you are using a username and password as your authentication details, you can choose not to

include those in the connection string (containing the details required to connect to the database)

when it is saved, because this string is saved in

plain text that would enable anyone who sees it to

have access to the database. In this case you would

have to provide these credentials to the model before

querying it in order for it to create a connection

to the database. If you don’t select the checkbox

to save the connection settings in the App.config

file you will also need to pass the model the details

on how to connect to the database before you can

query it.

In the next step, the wizard uses the connection

created in the previous step to connect to the

database and retrieve its structure (that is, its tables,

views, and stored procedures), which is displayed in

a tree for you to select the elements to be included

in your model (see Figure 29-4).

Other options that can be specified on this screen include:

.

Pluralize or Singularize Generated Object Names: This option (when selected) intelligently

takes the name of the table/view/stored procedure and pluralizes or singularizes the name

based on how that name is used in the model (collections will use the plural form, entities

will use the singular form, and so on).

.

Include Foreign Key Columns in the Model: The previous version of the Entity Framework

did not create properties for foreign key columns in the entities — opting to create a

relationship instead. However, in numerous scenarios this was not ideal, making it messy

to do some simple tasks due to the absence of these properties. In this new version you can

now select to include them in your entities by selecting this option.

.

Model Namespace: This enables you to specify the namespace in which all the classes

related to the model will be created. By default, the model will exist in its own namespace

(which defaults to the name of the model entered in the Add New Item dialog) rather than

the default namespace of the project to avoid conflict with existing classes with the same

names in the project.

Select all the tables in the database to be included in the model. Clicking the Finish button in this

screen creates an Entity Framework model that maps to the database. From here you can view the

model in the Entity Framework and adjust it as per your requirements and tidy it up as per your

tastes (or standards) to make it ideal for querying in your code.

the entity framework designer

Once the Entity Framework model has been generated, it opens in the Entity Framework designer,

as shown in Figure 29-5.

fiGure 29-4

Creating an entity Model .

627

fiGure 29-5

You’ll note that the designer has automatically laid out the entities that were created by the wizard,

showing the associations it has created between them.

You can move entities around on the designer surface, and the designer will automatically move the

association lines and try and keep them neatly laid out. Entities will automatically snap to a grid,

which you can view by right-clicking the designer surface and selecting Grid . Show Grid from the

context menu. You can disable the snapping by right-clicking the designer surface and unchecking

Grid . Snap to Grid from the context menu to have finer control over the diagram layout, but you

will find that entities line up better (and hence make the diagram neater) by leaving the snapping on.

As you move entities around (or add additional entities to) the diagram, you may find it gets a little

messy, with association lines going in all directions to avoid getting “tangled.” To get the designer

to automatically lay out the entities neatly again according to its own algorithms, you can right-click

the designer surface and select Diagram . Layout Diagram from the context menu.

Entity Framework models can quickly become large and difficult to navigate in

the Entity Framework designer. Luckily, the designer has a few tools to make

navigating it a little easier. The designer enables you to zoom in and out using

the zoom buttons in its bottom-right corner (below the vertical scrollbar — see

Figure 29-6). The button sandwiched between these zoom in/out buttons zooms

to 100% when clicked.

To zoom to a predefined percentage, right-click the designer surface and select one of

fiGure 29-6

the options in the Zoom menu. In this menu you will also find a Zoom to Fit option

(to fit the entire entity model within the visible portion of the designer), and a Custom option that

pops up a dialog enabling you to type a specific zoom level.

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In addition, selecting an entity in the Properties tool window (from the drop-down object selector)

automatically selects that entity in the designer and brings it into view; right-clicking the entity in

the Model Browser tool window (described shortly) and selecting the Show in Designer menu item

does the same. These make it easy to navigate to a particular entity in the designer, so you can make

any modifications as required.

You can minimize the space taken by entities

by clicking the icon in the top-right corner

of the entity. Alternatively, you can roll

up the Properties/Navigation Properties

groupings by clicking the +/– icons to their

left. Figure 29-7 shows an entity in its

normal expanded state, with the Properties/

Navigation Properties groupings rolled up

and completely rolled up.

You can expand all the collapsed entities in one go by right-clicking the designer surface and

selecting Diagram . Expand All from the context menu. Alternatively, you can collapse all the

entities in the diagram by right-clicking the designer surface and selecting Diagram . Collapse All

from the context menu.

A visual representation of an entity model (as provided by the Entity Framework designer) can

serve a useful purpose in the design documentation for your application. The designer provides a

means to save the model layout to an image file to help in this respect. Right-click anywhere on the

designer surface and select Diagram . Export as Image from the context menu. This pops up the

Save As dialog for you to select where to save the image. Note that it defaults to saving as a bitmap

(.bmp) — if you open the Save As Type drop-down list you will find that it can also save to JPEG,

GIF, PNG, and TIFF. PNG is probably the best choice for quality and file size.

It can often be useful (especially when saving a diagram for documentation) to display the property

types against each property for an entity in the designer. You can turn this on by right-clicking

the designer surface and selecting Scalar Property Format . Display Name and Type from the

context menu. You can return to displaying just the property name by selecting the Scalar Property

Format . Display Name item from the right-click context menu.

As with most designers in Visual Studio, the Toolbox and Properties tool

windows are integral parts of working with the designer. The Toolbox (as

shown in Figure 29-8) contains three controls: Entity, Association, and

Inheritance. How to use these controls with the designer is covered shortly.

The Properties tool window displays the properties of the selected item(s)

in the designer (an entity, association, or inheritance), enabling you to

modify their values as required.

In addition to the Toolbox and Properties tool windows, the Entity Framework designer also

incorporates two other tool windows specific to it — the Model Browser tool window and the

Mapping Details tool window — for working with the data.

fiGure 29-7

fiGure 29-8

Creating an entity Model .

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The Model Browser tool window (as shown

in Figure 29-9) enables you to browse the

hierarchy of both the conceptual entity model

of the database and its storage model. Clicking

an element in the Store model hierarchy shows

its properties in the Properties tool window;

however, these can’t be modified (because

this is an entity modeling tool, not a database

modeling tool). The only changes you can

make to the Store model is to delete tables, views, and stored procedures (which won’t modify the

underlying database). Clicking elements in the Conceptual model hierarchy also shows their properties

in the Properties tool window (which can be modified), and its mappings are displayed in the Mapping

Details tool window. Right-clicking an entity in the hierarchy and selecting the Show in Designer

menu item from the context menu brings the selected entity/association into view in the designer.

The second picture in Figure 29-9 demonstrates the searching functionality available in the Model

Browser tool window. As previously discussed, because your entity model can get quite large, it can

be difficult to find exactly what you are after. Therefore, a good search function is very important.

Type your search term in the search textbox at the top of the window and press Enter. In this

example the search term was Address, which highlighted all the names in the hierarchy (including

entities, associations, properties, and so on) that contained the search term. You’ll note that the

vertical scrollbar has the places in the hierarchy (which has been expanded) highlighted where

the search terms have been found, making it easy to see where the results were found throughout

the hierarchy. The number of results is shown just below the search textbox, next to which are an

up arrow and a down arrow to enable you to navigate through the results. When you are finished

searching you can click the cross icon next to these to return the window to normal.

The Mapping Details tool window (as shown in Figure 29-10) enables you to modify the mapping

between the conceptual model and the storage model for an entity. Selecting an entity in the

designer, the Model Browser tool window, or the Properties tool window shows the mappings in

this tool window between the properties of the entity to columns in the database. You have two

ways of mapping the properties of an entity to the database: either via tables and views, or via

functions (that is, stored procedures). On the left side of the tool window are two icons, enabling

you to swap the view between mapping to tables and views, to mapping to functions. However,

we’ll focus here just on the features of mapping entity properties to tables and views.

fiGure 29-9

fiGure 29-10

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The table/view mapping has a hierarchy (under the Column column) showing the table(s) mapped to

the entity, with its columns underneath it. To these columns you can map properties on your entity

(under the Value/Property column) by clicking in the cell, opening the drop-down list that appears,

and selecting a property from the list.

A single entity may map to more than one database table/view (bringing two or more tables/views

into a single entity, as previously discussed). To add another table/view to the hierarchy to map to

your entity, click in the bottom row where it says <Add a Table or View> and select a table/view

from the drop-down list. When you add a table to the Mapping Details tool window for mapping

to an entity, it automatically matches columns with the same name to properties on the entities and

creates a mapping between them. Delete a table from the hierarchy by selecting its row and pressing

the Delete key.

Conditions are a powerful feature of the Entity Framework that enable you to selectively choose

which table you want to map an entity to at run time based on one or more conditions that you

specify. For example, say you have a single entity in your model called Product that maps to a table

called Products in the database. However, you have additional extended properties on your entity

that map to one of two tables based on the value of the ProductType property on the entity — if

the product is of a particular type it will map the columns to one table, if it’s another type it will

map the columns to the other table. You can do this by adding a condition to the table mapping. In

the Mapping Details window click in the row directly below a table to selectively map where it says

<Add a Condition>. Open the drop-down list that appears, which will contain all the properties

on the entity. Select the property to base your condition on (in the given example it would be the

ProductType property), select an operator, and enter a value to compare the property to. Note that

there are only two operators: equals (=) and Is. You can add additional conditions as necessary to