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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:

Example site structure

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.

Entity Model

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 4.4. 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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