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{{Header|Handling BLOBs}}


In the data model you can define BLOB attributes. This attributes are objectified using an instance of a particular object implementing the '''RTXBLOBData''' interface. This type of object permits to access some properties of the wrapped BLOB:
*'''name''': the file name
*'''length''': the file size in bytes
*'''extension''': the file extension

You can use the following data unit template to see BLOB information.

<code><pre>
[% def file = unit.selectSingleNode("layout:Attribute[@name='file']") %]

upload path: ${<wr:UnitId/>.data.[%= getFieldName(file)%]}
name: ${<wr:UnitId/>.data.[%= getFieldName(file)%].name}
length: ${<wr:UnitId/>.data.[%= getFieldName(file)%].length}
extension: ${<wr:UnitId/>.data.[%= getFieldName(file)%].extension}    
</pre></code>

In the Web page you will see something like

<code><pre>
upload path: /upload/ent1/1/test.pdf
name: test.pdf
length: 2000
extension: pdf
</pre></code>

The following code according to the ''Storage Type''
<code><pre>${<wr:UnitId/>.data.[%= getFieldName(file)%]}</pre></code>
represents
*the path of the file stored on the file system under the Web application "upload" folder, if the BLOB attribute is stored '''on the file system'''
*a query string describing how to retrieve the BLOB binary data, if the BLOB attribute is stored '''on the database'''

=== A working example ===

For example if you want to render an image into the HTML page you can use one of the following templates depending on the chosen ''Storage Type'' 
*BLOB stored on file system
<code><pre><a href="${<wr:UnitId/>.data.[%= getFieldName(file)%]}">
  <c:out value="${<wr:UnitId/>.data.[%= getFieldName(file)%].name}"/>
</a>
</pre></code>
*BLOB stored on the database<code>
<pre><a href="<webratio:BLOB value="${<wr:UnitId/>.data.[%= getFieldName(file)%]}"/>">
  <c:out value="${<wr:UnitId/>.data.[%= getFieldName(file)%].name}"/>
</a>
</pre></code>

{{Semantic
  |category=Presentation
  |sort=Blob
  |difficulty=Intermediate
  |technology1=Database
  |technology2=JSP
  |technology3=WRTags
  |argument1=Styling Guidelines
  |argument2=BLOBs
  |refers1=Style Project
  |uses1=Template
  |uses2=Data Unit
}}