Confusion with get_blob_file_src

Question

Hi,
Simple requirement: I have photos stored in a BLOB column in a table and I want them displayed
thumbnail size in an interactive-report page.
Having read round this area, it seems that I am duty bound to call apex_util.get_blob_file_src from
the report query's SELECT statement (so that I can force the image size to be 75 by 75).
Here's where the problems start.
Having read the advice, it seems that my select query should have a column along the lines
of: '<img src="'||APEX_UTIL.GET_BLOB_FILE_SRC('P2_ATTACHMENT',:P2_EMPNO)||'" />'
(I copied this from the documentation).
All looks fine: it's the return of the package APEX_UTIL's function called "GET_BLOB_FILE_SRC" wrapped
inside bookends of "<img src=" and "/>" essentially.
So this gets me thinking... the GET_BLOB_FILE_SRC looks like it takes two parameters. The
first parameter is obviously an item name, and the second is an item value.
But when I edit my interactive report page there is a single region for the interactive report and
there are no explicit items in the "Items" section underneath that.
Back to the API manual: I'm reading the description of the first parameter of the GET_BLOB_FILE_SRC
function and it says "Name of valid application page ITEM that with type FILE that contains the source type of DB column."
Hmmm... "Name of valid application page ITEM" ... I don't have one, so maybe I should create one for
use here. What to call it for this page three... how about "P3_IMAGE_HIDDEN" (because I'm thinking that its acting as
some sort of Placeholder box but although I want to use it I don't want to see it on its own).
Next bit of manual: "with type FILE"... does that mean this item's "DISPLAY AS" attribute has to be
set to "FILE"? Lets see... there's only a "File Browse..." entry that looks similar so I'm forced to choose
that.
I wonder if the option "FILE" is available through any other attributes... can't see any so let's persevere.
Then I read "... that contains the source type of DB column".
Gosh: what on earth does that mean? Does it mean that the contents of this Item is somehow "sourced" against
the specific blob column in the database?
So I set the "Source Type" to "Database Column" and then fill in the Source box with the name of the blob column
from the table.
(incidental aside: I find it amusing when I read some bits of the manual which explain that some words are case
sensitive when it might be more useful to state that upper case is the only one that will work! Look at the help
for "Source Type" and at the end of the "Database Column" entry it says "The database column name in that field is case sensitive."
The entry is not wrong, it's just that it could be more helpful methinks!)
Quick recap: The call to function GET_BLOB_FILE_SRC seems to take two parameters: the name of a legitimate Item
that is linked to the database table column, and the primary key value of one row from the table in question.
How this system works out which table holds the important blob column is a mystery to me.
When I set the report field to "Display as text" I get to see the end product of the query: a field that looks like
the following copy-and-paste:
<code>
<img src="apex_util.get_blob_file?a=900&s=3134319599265367&p=3&d=&i=1721302456803667&p_pk1=115&p_pk2=&p_ck=B7851B908E84506147F19B155D36C5F3" height="75" width="75" />
</code>
But when I change the report field to "Standard Database Column", all I see is a broken link.
Blast (and similar expletives).
I've had a quick look at the copy-and-pasted thing above and I can make guesses at the parameters such
as "a=900" (I've numbered this application 900), "p=3" it's page three, "p_pk1=115" looks like the first
primary key value etc. But what's the "d=" for ? Is that the source of my troubles?
Time to re-throw myself on the mercy of the group. Help requested please; thanks in advance.
Mungo Henning

Answer 1

Hello
OK. This is my understanding of how the 'get_blob_file_src ' API works. This API is a wrapper over the procedure 'get_blob_file'. The API returns a mod/plsql URL that calls out to 'apex_util.get_blob_file'.
So in order to call 'get_blob_file' we need values for the following parameters (see end of post for a desc of get_blob_file)
s Apex Session Id
a Apex Application Id
p APEX page id
d Process-id of the ARP page process in page p
p_pk1 Primary key value
p_ck1 Checksum
However, get_blob_file_src is called in the report query with just 2 parameters. These are
p_item_name - Name of page item of type FILE and source type of 'Database Column' and the column name being the name of the column that has the BLOB data
p_v1 - Value of the primary key column of the table that has the BLOB column
Now, how are the values for the parameters required by 'get_blob_file' obtained by get_blob_file_src ?
s -> is available from session state
a -> is available from session state
p -> is obtained by looking up the APEX meta data for the page-id of the page-item specified as the first parameter to get_blob_file_src
d -> This is the interesting one. A hack at best to obtain the table_name and PK column of the table containing the BLOB  from APEX meta data!
On the page specified in 'p' there must exist a ARP DML process with the following specs.
owner -> owner of table from where the blob column is to be retrieved
table_name -> name of the table that has the blob column to be retrieved
Item Containing PK -> Specify any string
Primary Key Column -> PK column of the table that has the blob column to be retrieved
Process Point -> After Submit..
p_pk1 -> is the value specified as the 2nd parameter to get_blob_file_src
p_ck1 -> presumably generated
Given the above and a report against the DEMO_PRODUCT_INFO table with a query likeselect product_id, '<img HEIGHT="25" WIDTH="25" src="'||apex_util.get_blob_file_src('P96_X',PRODUCT_ID)||'" />' img
FROM
DEMO_PRODUCT_INFOwhat I had to do make the images render was to
Create a page with an IR report region with the above query
Create another page where I defined a 'file-browse' type page item named P96_X. Set the Source Type to 'Database Column' and column name to PRODUCT_IMAGE
Created a ARP DML page process on this page with the following specifications
Owner => DEMO
Table Name => DEMO_PRODUCT_INFO
Page Item for PK => P1_ID
Primary Key Column => PRODUCT_ID
Process Point - On Submit..
Doc for get_blob_file extracted from package spec (APEX_UTIL)
procedure get_blob_file(
    -- Automatically called from APEX form pages
    -- Not designed to be called proceduarlly
    -- Calls to this procedure can be generated by calling the apex_util.get_blob_file_src function
    -- Page must have item of type FILE (FILE Browse)
    -- Page item source must use the following format "DB_COLUMN:MIMETYPE_COLUMN:FILENAME_COLUMN:LAST_UPDATE_COLUMN:CHARSET_COLUMN:CONTENT_DISPOSITION:DOWNLOAD_LINK"
    --    DB_COLUMN           = Required case sensitive name of a valid column which is of type BLOB
    --    MIMETYPE_COLUMN     = Optional case sensitive column name of a table column used to store the mimetype
    --    FILENAME_COLUMN     = Optional case sensitive column name of a table column used to store the file name
    --    LAST_UPDATE_COLUMN  = Optional case sensitive column name of a table column used to store the last update date of the BLOB
    --    CHARSET_COLUMN      = Optional case sensitive column name of a table column used to store the file character set
    --    CONTENT_DISPOSITION = inline or attachment
    --    DOWNLOAD_LINK       = Optional text to be used for the download text, defaults to Download, translated
    -- Page item source must include at least the database column name and a trailing colon
    -- Mimetype column is required if the mimetype is to be encoded in the download header
    -- Page item must be of source type of DATABASE COLUMN
    -- Page must have a DML process of type DML_PROCESS_ROW, used to determine the tablename
    -- Must be called from an APEX application context
    -- Invalid inputs will result in a 404 error
    s                     in number,                -- APEX session ID
    a                     in number,                -- APEX application ID
    p                     in number,                -- APEX page ID of the form page
    d                     in number,                -- DML process APEX meta data ID
    i                     in number,                -- ITEM of type FILE APEX meta data ID
    p_pk1                 in varchar2,              -- Primary key value
    p_ck                  in varchar2,              -- Checksum used to prevent URL Tampering
    p_pk2                 in varchar2 default null, -- Optional Second Primary Key Value, used for compound keys
    p_mimetype            in varchar2 default null, -- Optional ...
    p_content_disposition in varchar2 default null, -- Optional use "inline" or "attachment" all other values ignored
    p_show_last_mod       in varchar2 default 'Y'); -- Optional ...Varad
Edited by: varad acharya on Oct 27, 2009 2:44 PM