Rendering a Direct to Web Page: An Example

Rendering a Direct to Web Page: An Example

This section describes how the components, the Direct to Web context, and the Direct to Web factory interact while creating and rendering a query page for the Movie entity. This example begins with the user viewing a query all page in the Basic look and clicking a hyperlink labeled "more.." in the Movie row, which links to the query page. The query all page is rendered using a BASQueryAllEntitiesPage.wo template.

Creating the Query Page

When the user clicks the hyperlink, the hyperlink invokes the showRegularQueryAction method defined in the D2WQueryAllEntitiesPage class, the superclass of the BASQueryAllEntitiesPage class. Listing 3-2 shows the implementation of the showRegularQueryAction method.

Listing 3-2 D2WQueryAllEntitiesPage.showReqularQueryAction

public WOComponent showRegularQueryAction()
{
    QueryPageInterface newQueryPage = D2W.factory().queryPageForEntityNamed
        (entity().name(),session());
    return (WOComponent)newQueryPage;
}

The Direct to Web factory object creates a Direct to Web context and initializes its NSDictionary by setting the value for the task key to "query" and the value for the entity key to the Movie EOEntity.

**Table 3-6 Initial Direct to Web context dictionary**
Key	Value
`task`	"query"
`entity`	<EOEntity Movie>

To determine which Direct to Web template to create, the Direct to Web factory asks the Direct to Web context for the value of the pageName key. Since this key is neither in the dictionary nor a derived value from the dictionary, the Direct to Web context enlists the aid of the rule engine. Listing 3-3 shows the rules that resolve the key.

Listing 3-3 Rules used to resolve the pageName key

((look = "BasicLook") and (task = "query")) => pageName = "BASQueryPage"

*true* => look = "BasicLook"

A rule has a left-hand side and a right-hand side separated by "=>". The left-hand side specifies a condition that must be met for the rule to be a candidate to "fire," or resolve a key. The right-hand side specifies the key-value assignment that takes place when the rule fires. Since the left-hand side for the second rule is true, the rule always fires when the Direct to Web context wants the value for the look key.

There are three sources for the rules that the rule engine uses:

The Direct to Web framework defines rules that determine the default application behavior.

You can write your own rules that override the framework's defaults rules.

The Web Assistant generates rules involving the specific application information. These rules are generated automatically as you configure the application with the Web Assistant; you don't have to write them.

See "The Rule System" for more information about rules.

The two rules that resolve the pageName key (defined in the Direct to Web Framework) fire and the Direct to Web context returns "BASQueryPage" as the value for the pageName key.

Knowing the template name, the Direct to Web factory object creates a page using the WOComponent.pageWithName method. Then it attaches the Direct to Web context to the newly generated page.