Silva: Silva File Object

Silva File Object

Meta:

Valid for:  Silva 0.9.3
Author:     Jan-Wijbrand Kolman
            Martijn Faassen
Email:      jw+infrae.com
CVS:        $Revision: 1.8 $ $Date: 2004/04/17 10:12:49 $

Introduction

Silva's main objective is to store, manipulate and publish structured, mainly textual, content. However not all content, such as files and images, is deeply structured in such a way. The File object can be used to store arbitrary files in an unstructured manner into Silva. Authors may reference these File objects with hyperlinks from documents. This way, site visitors are able to download and view or use this file.

A web browser can recognize what kind of file content it is dealing with by using the file's mime type. Using the mime type the browser can be configured to take special action for particular files; it could for instance open the file in Word in case of a Word document, or play an MP3 file in an MP3 music player. The Silva File object determines the mime type of the file automatically and provides it to the user's browser. The mime type of the file object is also used by Silva to display a relevant icon in the ZMI. If the mime type is not recognized, it will default to 'application/octet- stream'.

Creation

In order to create a File object, select the Silva File object from the new object menu in the ContentsTab of a container. This will bring up the add screen to create a silva file. There the user can fill in the id and title as with any Silva object and provide a file on the local computer of the user to upload. Unlike what is the case for other Silva objects the id field is not actually required. Instead the user can just provide the file for upload and Silva will derive the id from its filename automatically.

In case of large files, the upload action to Silva may take a while. After that, the file object will have been created as a Silva asset. The asset will appear in the bottom of the ContentsTab of the container.

Editor

The editor tab of the File object does not provide much more functionality than a way to change the file's title and a button to upload a new version of the file. If by any chance the new file has a different type Zope will automatically detect the new mime type and change the File object's icon correspondingly.

Storage

By default, Silva stores file content in the Zope Object Database (ZODB). Because the file content is potentially very large it may be preferable to store the contents on the file system instead, to avoid excessively growing the size of the ZODB. A site administrator can configure the storage behavior of the file object per Silva installation, or even more fine-grainedly on a Silva folder basis if necessary. Note that whether the file content is stored in ZODB or on the file system is completely transparent to a Silva author.

To store file content on the filesystem the ExtFile product [1] needs to be installed in Zope. If this product is not installed, it will automatically choose the ZODB for storing file contents. After installing ExtFile, go to service_files of your Silva root and check the `Enable filesystem storage' box.

Note that you can create a new Silva File Service (called 'service_files') in any container. Thus it is possible to enable or disable file system storage of a particular Silva subsite selectly or to save the file contents in a different location on the filesystem.

API

A File object overrides the Silva 'index_html()'. This method, and the more explicit "download()" method invoke a file download on the Visitor's webbrowser. The 'get_download_url()' and 'get_download_link()' method return (for e.g. page templating) an URL and a complete '<a href>' tag respectively.

The file's mime type maybe retrieved with the 'get_content_type()' method.

Caveats / ToDo

Each File object stored on the file system contains the path to the file. Thus moving the file on the file system, will break the corresponding Silva File object.

For correct mime types and file extensions, the File object uses the Python 'mimetools' and 'mimetypes' modules. I'm not sure how up-to-date these lists are.

References

[1] ExtFile

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