Re: Storing small image files - Mailing list pgsql-general

Thanks Karl, but I'm trying to do this from a psql shell. I can't use the C functions there, can I?

On Thu, May 9, 2013 at 11:21 AM, Karl Denninger <karl@denninger.net> wrote:

On 5/9/2013 11:12 AM, Karl Denninger wrote:

On 5/9/2013 10:51 AM, Achilleas Mantzios wrote:

Take a look here first :

http://www.postgresql.org/docs/9.2/interactive/datatype-binary.html

 

then here : http://www.dbforums.com/postgresql/1666200-insert-jpeg-files-into-bytea-column.html

 

didnt try it myself tho.

 

Most of the time people manipulate bytea's using a higher level programming lang.

 

 

On Πεμ 09 Μαΐ 2013 10:34:35 Nelson Green wrote:

On Thu, May 9, 2013 at 10:20 AM, Achilleas Mantzios <achill@matrix.gatewaynet.com> wrote:

why not bytea?

Hi Achilleas,

Actually I was asking if bytea is the correct datatype, and if so, would someone mind providing a simple example of how to insert and retrieve the image through the psql client.

Let's say I have an employee named Paul Kendell, who's employee ID is 880918. Their badge number will be PK00880918, and their badge photo is named /tmp/PK00880918.jpg. What would the INSERT statement look like to put that information into the security_badge table, and what would the SELECT statement look like to retrieve that record?

Thanks for your time.

 

much more control, much more information, IMHO.

In our DB evolving from an initial 7.1 back in 2001, and currently on 9.0,

we have been storing everything binary in bytea's.

 

There are downsides in both solutions, you just have to have good reasons

to not use bytea.

 

On Πεμ 09 Μαΐ 2013 10:04:18 Nelson Green wrote:

Good morning list,

I am designing a system that will have a table for security badges, and we want to store the ID badge photo. These are small files, averaging about 500K in size. We have made the decision to store the image as a BLOB in the table itself for a variety of reasons. However, I am having trouble understanding just how to do that.

The table structures:

CREATE TABLE employee
(
   employee_id                    INTEGER             NOT NULL,
   employee_lastname              VARCHAR(35)         NOT NULL,
   employee_firstname             VARCHAR(35)         NOT NULL,
   employee_mi                    CHAR(1),
   PRIMARY KEY (employee_id)
);

CREATE TABLE security_badge
(
   badge_number                   CHAR(10)            NOT NULL,
   employee_id                    INTEGER             NOT NULL
      REFERENCES employee(employee_id),
   badge_photo                    ????,
   PRIMARY KEY (badge_number)
);

What datatype should I use for the badge_photo (bytea?), and what are the commands to insert the picture accessing the server remotely through psql, and to retrieve the photos as well, please?

Thanks,
Nelson

-

Achilleas Mantzios

IT DEV

IT DEPT

Dynacom Tankers Mgmt

-

Achilleas Mantzios

IT DEV

IT DEPT

Dynacom Tankers Mgmt

To encode:


write_conn = Postgresql communication channel in your software that is open to write to the table

char    *out;
size_t    out_length, badge_length;

badge_length = function-to-get-length-of(badge_binary_data);  /* You have to know how long it is */

out = PQescapeByteaConn(write_conn, badge_binary_data, badge_length, &out_length); /* Convert */

That function allocates the required memory for the conversion.  You now have an encoded string you can "insert" or "update" with.  Once you use it in an "insert" or "update" function you then must "PQfreemem(out)" to release the memory that was allocated.

To recover the data you do:

PQresult *result;

result = PQexec(write_conn, "select badge_photo blah-blah-blah");
....
out = PQunescapeBytea(PQgetvalue(result, 0, 0)); /* Get the returned piece of the tuple and convert it */

"out" now contains the BINARY (decoded) photo data.  When done with it you:

PQfreemem(out) to release the memory that was allocated.

That's the rough outline -- see here:

http://www.postgresql.org/docs/current/static/libpq-exec.html

--
Karl Denninger
karl@denninger.net
Cuda Systems LLC

Oops -- forgot the second parameter on the "PQunescapebytea" call :-)

Yeah, that would be bad:

size_t out_length;

out = PQunescapeBytea(PQgetvalue(result, 0, 0), &out_length); /* Get the returned piece of the tuple and convert it */

Otherwise, being binary data, how would you know how long it is? :-)

BTW I use these functions extensively in my forum code and have stored anything from avatars (small image files) to multi-megabyte images. Works fine.  You have to figure out what the type of image is, of course (or know that in advance) and tag it somehow if you intend to do something like display it on a web page as the correct mime type content header has to be sent down when the image is requested.  What I do in my application is determine the image type at storage time (along with width and height and a few other things) and save it into the table along with the data.

--
Karl Denninger
karl@denninger.net
Cuda Systems LLC