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| <title>Filter Transformer</title> |
| <link href="http://purl.org/DC/elements/1.0/" rel="schema.DC"> |
| <meta content="Carsten Ziegeler" name="DC.Creator"> |
| <meta content="Sven Beauprez" name="DC.Creator"> |
| <meta content="Davanum Srinivas" name="DC.Creator"> |
| <meta content="This document describes the Filter transformer of Cocoon." name="DC.Description"> |
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| <body> |
| |
| <h1>Filter Transformer</h1> |
| |
| <p>The filter transformer can be used to let only an amount of elements |
| through in a given block.</p> |
| |
| <ul> |
| |
| <li>Name : filter</li> |
| |
| <li>Class: org.apache.cocoon.transformation.FilterTransformer</li> |
| |
| <li>Cacheable: no.</li> |
| |
| </ul> |
| |
| <p> |
| When you for example query a database and it returns too many rows too process at once, you |
| might want to take a block of elements, process this block and ignore the rest |
| for now. You can best compare it to a search on Google: they only return 10 |
| results in one time, for more results you have to click on another block (page). |
| It wouldn't be wise to process more than 10 elements in the pipeline if you only |
| need to display 10 elements. |
| </p> |
| |
| <p> |
| Assume that a query returns 56 row elements (by using the SQLTransformer) and |
| that you only want to display the first 10 elements: |
| </p> |
| |
| <p> |
| Output XML from the SQLTransformer: |
| </p> |
| |
| |
| <pre class="code"> |
| |
| <rowset nrofrows="56" name="test" |
| xmlns="http://apache.org/cocoon/SQL/2.0"> |
| <row> |
| <!-- db record --> |
| </row> |
| <row> |
| <!-- db record --> |
| </row> |
| <row> |
| <!-- db record --> |
| </row> |
| |
| ... |
| |
| <row> |
| <!-- db record --> |
| </row> |
| </rowset> |
| |
| </pre> |
| |
| |
| <p> |
| By adding following lines to the sitemap, just under the SQLTransformer, you |
| restrict the results to 10 elements in the first block: |
| </p> |
| |
| |
| <pre class="code"> |
| |
| <map:transform type="filter"> |
| <map:parameter name="element-name" value="row"/> |
| <map:parameter name="count" value="10"/> |
| <map:parameter name="blocknr" value="1"/> |
| </map:transform> |
| |
| </pre> |
| |
| |
| <p> |
| output XML: |
| </p> |
| |
| |
| <pre class="code"> |
| |
| <rowset nrofrows="56" name="test" |
| xmlns="http://apache.org/cocoon/SQL/2.0"> |
| <block id="1"> |
| <row> |
| <!-- db record --> |
| </row> |
| |
| <!-- total of 10 rows --> |
| |
| <row> |
| <!-- db record --> |
| </row> |
| </block> |
| <block id="2"/> |
| <block id="3"/> |
| <block id="4"/> |
| <block id="5"/> |
| <block id="6"/> |
| </rowset> |
| |
| </pre> |
| |
| |
| <p> |
| To make it more dynamically, put something like {reqCount} and {reqBlock} in the |
| values for count and blocknr respectively. These can be parameters from the |
| request and they can be passed to the sitemap with an action. |
| </p> |
| |
| <p> |
| The FilterTransformer is a standalone component, you don't need to use it in |
| combination with the SQLTransformer. |
| </p> |
| |
| |
| </body> |
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