Mediaget/getimage

Question

I have the following stored procedure to get images from the database to into my asp.
PROCEDURE GETIMAGE (
ord_procedure_path in varchar2,
http_if_modified_since in varchar2,
http_status out varchar2,
http_last_modified out varchar2,
http_redirect out varchar2,
ord_content_type out varchar2,
ord_content_length out number,
ord_content_blob out blob,
ord_content_bfile out bfile
as
localImage ordsys.ordimage;
begin
* Retrieve the image object from the database into a local object.
select IMAGE into localImage from PD_UPLOAD_IMAGE where SEQ = ord_procedure_path;
* Figure out the status of the client's cache. If the client's cache
* is up to date, then we can return immediately.
http_status := ordwebutl.cache_status( localImage.getUpdateTime(),
http_if_modified_since,
http_last_modified );
if http_status = 304 then
return;
end if;
* Figure out where the image is.
if localImage.isLocal() then
* The image is stored locally in the localData BLOB attribute
ord_content_type := localImage.getMimeType();
ord_content_length := localImage.getContentLength();
ord_content_blob := localImage.getContent();
elsif upper( localImage.getSourceType() ) = 'FILE' then
* The image is stored as a file from which ORDSource creates a BFILE.
ord_content_type := localImage.getMimeType();
ord_content_length := localImage.getContentLength();
ord_content_bfile := localImage.getBFILE();
elsif upper( localImage.getSourceType() ) = 'HTTP' then
* The image is referenced as an HTTP entity, so we have to redirect
* the client to the URL which ORDSource provides.
http_status := 302;
http_redirect := localImage.getSource();
else
* The image is stored in an application-specific location for
* which no default action is available.
null;
end if;
end;
This works just fine, now i want to transform the procedure so it returns thumbnails of the original image.
i tried to put folowing code right after the select
localImage.process('maxScale=32 32');
localImage.setproperties;
but it never returns thumbnails
(500 internal server error)
how do i have to transform my code to get back thumbnails without changing the original image in the database of course
thx

Answer 1

Hi,
This is failing because BLOBs have to be locked before they can be written. (By default, the Web Agent uses HTTP errors. Change the request from .../mediaget/... to .../~mediaget/... and you'll see the real SQL error.)
However, if you change the SELECT statement to include FOR UPDATE, then you'll end up permanently changing the data in the database, which is not what you want. (The Web Agent does a commit at the end of each successful request.)
The most efficient approach would be to create a thumbnail column in the table, and store the thumb-nail images there. Thumb-nail images could be created either when media is inserted into the database or the first time a thumb-nail is requested by a client. Alternatively, you can always create a thumb-nail at retrieval time, but image processing such as this is a relatively expensive operation - it would certainly slow down the server if you had lots of concurrent users, all retrieving thumb-nail images.
If you still want to create a thumb-nail dynamically (throwing it away once its been delivered to the client), you can use a temporary BLOB. For example, you could do something like the following (WARNING: typed, but not tested!!).
In the declarative section, add:
thumbnail ordsys.ordimage;Leave the SELECT statement alone (don't add FOR UPDATE), and create the thumb-nail image as follows. See "Oracle8i Supplied PL/SQL Packages Reference" for more information on the DBMS_LOB package and the dbms_lob.createTemporary method. See "Oracle8i Application Developer's Guide - Large Objects (LOBs)" for more information on LOBs in general.
thumbnail := ordsys.ordimage.init();
dbms_lob.createTemporary( thumbnail.source.localdata,
true,
dbms_lob.session );
localImage.processCopy( thumbnail, 'maxScale=32 32' );
ord_content_type := thumbnail.getMimeType();
ord_content_length := thumbnail.getContentLength();
ord_content_blob := thumbnail.getContent();The Web Agent automatically frees temporary BLOBs once the data has been delivered to the client.
Hope this helps,
Simon
null