Content Application Developer Manual / 4.2.2.3 Example Data View Design

Content Application Developer Manual / Version 2301

4.2.2.3 Example Data View Design

This section illustrates the process of defining a data view configuration. For this example, a simple site with three pages is used. The first page consists of a brief overview of two articles that are completely shown on two separate pages. These article instances are shared between the overview page and the detail pages:

Figure 4.2. Example site structure

The entities are represented as beans and properties where the properties are assumed to have different costs: Some are expensive to compute while others are cheap.

Figure 4.3. Entity Model

Bean	Property	Description	Expensive
`PageBean`	`Title`	The page's title.	No
	`Content`	The page content as a linked `OverviewBean` or `ArticleBean`.	No
	`Navigation`	All `PageBeans` to be rendered as navigation.	Yes
`ContentBean`	`Page`	The `PageBean` which embeds this bean.	Yes
`OverviewBean`	`Teasers`	A list of `ArticleBeans` to be rendered as teasers.	No
`ArticleBean`	`Headline`	The article's headline.	No
	`Text`	The article's text.	Yes
	`Abstract`	The article's abstract which is extracted from property `Text` automatically.	Yes*
	`Image`	An optional link to an image.	No
`ImageBean`	`MimeType`	The image data's mime type.	Yes
	`Data`	The binary data.	No

Table 4.3. Bean Properties in the DataView Example. (*) The computation of property "abstract" is not expensive by itself but the access of property "text" only.

The JSP templates for rendering the beans are modeled as follows:

PageBean.jsp

<html>
<head>
  <title><c:out value="${self.title}"/></title>
</head>
<body>
  <div class="content"><cm:include self="${self.content}"/>
   </div>
  <div class="navigation">
    <ul>
      <c:forEach items="${self.navigation}" var="page">
        <li><a href="<cm:link target='${page}'/>">
         <c:out value="${page.title}"/></a></li>
      </c:forEach>
    </ul>
  </div>
</body>
</html>

ArticleBean.jsp

<h1><c:out value="${self.headline}"/></h1>
<div><c:out value="${self.text}"/></div>
<c:if test="${!empty self.image}">
  <img src="<cm:link target='${self.image}'/>" alt="image"/>
</c:if>

OverviewBean.jsp

<c:forEach items="${self.teasers}" var="article">
  <h2><c:out value="${article.headline}"/></h2>
  <p>
    <c:out value="${article.abstract}"/>
    [<a href="<cm:link target='${article.page}'/>">more</a>]
  </p>
</c:forEach>

Considering the above mentioned settings, the following dataviews.xml file can be derived:

<?xml version="1.0"?>
<dataviews xmlns=
"http://www.coremedia.com/2004/objectserver/dataviewfactory">

 <dataview appliesTo="com.mycompany.PageBean">
  <property name="content" associationType="dynamic"/>
  <property name="navigation" associationType="static"/>
 </dataview>

 <dataview appliesTo="com.mycompany.ArticleBean">
  <property name="page" associationType="static"/>
  <property name="text"/>
 </dataview>

 <dataview appliesTo="com.mycompany.OverviewBean">
  <property name="teasers" associationType="dynamic"/>
 </dataview>

 <dataview appliesTo="com.mycompany.ImageBean">
  <property name="mimeType"/>
 </dataview>

</dataviews>

All expensive associations (PageBean#Navigation and ArticleBean#Page) are declared to be data viewed using the default association type "static". Please note, that OverviewBean#Page is not marked here since this is not accessed by the templates. PageBean#Content and OverviewBean#Teasers are marked with the association type "dynamic" although they are not expensive: Instead they are used making ArticleBean recursively reachable from the PageBean. Finally, the non-associating but expensive properties ArticleBean#Text and ImageBean#MimeType are marked for caching as well. ArticleBean#Abstract is not marked here because it benefits from the already cached ArticleBean#Text.

Keep in mind that a perfect data view configuration depends on a lot of circumstances. Let's say that the underlying contents are updated very rarely on the one hand but accessed very often on the other hand. In order to reduce the number of cache read operations, some property associations might be switched to "composition". An additional "teaser" data view might be introduced in order to cache the ArticleBean's different views (overview and detail) with separate objects.

<dataviews xmlns=
"http://www.coremedia.com/2004/objectserver/dataviewfactory">

 <dataview appliesTo=
 "com.coremedia.objectserver.dataviews.examples.PageBean">
  <property name="content" associationType="composition"/>
  <property name="navigation" associationType="static"/>
 </dataview>


 <dataview appliesTo=
 "com.coremedia.objectserver.dataviews.examples.ArticleBean">
  <property name="text"/>
 </dataview>

 <dataview appliesTo=
 "com.coremedia.objectserver.dataviews.examples.ArticleBean"
name="teaser">
  <property name="abstract"/>
  <property name="page" associationType="static"/>
 </dataview>

 <dataview appliesTo=
 "com.coremedia.objectserver.dataviews.examples.OverviewBean">
  <property name="teasers" associationType="composition"
   dataview="teaser"/>
 </dataview>

 <dataview appliesTo=
"com.coremedia.objectserver.dataviews.examples.ImageBean">
  <property name="mimeType"/>
 </dataview>

</dataviews>

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