Subject Re: [firebird-support] Blob Fields
Author Helen Borrie
At 11:41 AM 9/08/2004 -0300, you wrote:
>I didnt know "filters" before, so I want to understand it. Maybe it can
>make my life easier. I need to store pictures, and other files in the
>database. Where could I find more info about it?

You already can store binary files in blobs. The engine doesn't know or
care what you store there - pictures, documents, whatever.

A blob filter is a special kind of external function ("UDF") or routine
that someone writes according to some rules, in C, C++, Pascal, etc., for
converting a lump of data from one format to another. So, e.g. you could
write a blob filter to convert a blob of XML text into HTML or RTF; or one
to convert a jpeg into a portable net graphic (png). You assign negative
numbers as subtypes for your blobs and then, in use, you ask the engine to
invoke your blob filter to take a blob of one subtype and convert it to

In the database, you declare a filter (using DECLARE FILTER) much as you
declare external functions (DECLARE FUNCTION).

Paul Beach wrote a paper about blob filters, based on his talks at Fulda in
2003 and 2004. Search the IBPhoenix web site.

Would you please trim your replies.