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>Pgtcl Reference Manual: The PostgreSQL Tcl Interface</TH
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>5.10. Example - Bytea Escaping - Picture Viewer, Part 2 - View Pictures</A
></H1
><P
>This example is a variation of the GIF picture viewer shown in
<A
HREF="pgtcl-example-picview-pq.html"
>Section 5.8</A
>. It also stores the images
as <TT
CLASS="LITERAL"
>bytea</TT
> fields in the database, but rather than
using prepared queries in binary mode, it uses normal text mode queries.
In order to get the binary data through normal SQL queries intact,
the commands <A
HREF="pg-escape-bytea.html"
>pg_escape_bytea</A
>
and <A
HREF="pg-unescape-bytea.html"
>pg_unescape_bytea</A
> are used.
This version is generally less efficient that using binary prepared
queries, and can be significantly slower.</P
><DIV
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><P
><B
>Note: </B
><CODE
CLASS="FUNCTION"
>pg_escape_bytea</CODE
> and <CODE
CLASS="FUNCTION"
>pg_unescape_bytea</CODE
>
are extensions added to
<SPAN
CLASS="APPLICATION"
>pgtcl-ng</SPAN
> version 1.5.2 and
<SPAN
CLASS="APPLICATION"
>pgin.tcl</SPAN
> version 2.2.0.
This example will not work with other versions or implementations.</P
></BLOCKQUOTE
></DIV
><P
>Given an identifier on the command line, it attempts to retrieve and
display the stored picture with that identifier.</P
><P
>See <A
HREF="pgtcl-example-picstore-esc.html"
>Section 5.9</A
> for the program used to
insert the pictures in the database.
(Since the same schema is used, the script in
<A
HREF="pgtcl-example-picstore-pq.html"
>Section 5.7</A
> can also be used.)</P
><P
>This example runs under <SPAN
CLASS="APPLICATION"
>wish</SPAN
>, not
<SPAN
CLASS="APPLICATION"
>tclsh</SPAN
>. It also assumes database connection
information is provided through the environment.</P
><DIV
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><A
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></A
><P
><B
>Example 5-16. Bytea Escaping - View Pictures Stored in Database</B
></P
><PRE
CLASS="PROGRAMLISTING"
>#!/usr/bin/wish
# Example - picture storage as bytea, using escape/unescape:
package require Pgtcl
# Return the picture data identified by 'name'.
# Throw an error if it can't be read.
proc get_picture {conn name} {
# Note that for a text-mode query on a BYTEA column, PostgreSQL will escape
# the data for us.
set result [pg_exec $conn "SELECT picture FROM pics\
WHERE pname='[pg_escape_string $name]'"]
if {[pg_result $result -status] != "PGRES_TUPLES_OK"} {
set message [pg_result $result -error]
pg_result $result -clear
error "Error: Query failed: $message"
}
if {[set n [pg_result $result -numTuples]] != 1} {
pg_result $result -clear
error "Error: Query returned $n results"
}
# Unescape and return the data, which is the only column in the only row:
set data [pg_unescape_bytea [lindex [pg_result $result -getTuple 0] 0]]
pg_result $result -clear
return $data
}
if {$argc != 1} {
puts stderr "Usage: view_picture name"
exit 1
}
set name [lindex $argv 0]
# Connect to the database.
set conn [pg_connect -conninfo ""]
# Get the picture data:
set failed [catch {get_picture $conn $name} data]
# Done with database connection:
pg_disconnect $conn
# Exit if unable to retrieve the data:
if {$failed} {
puts "Failed to view picture '$name': $data"
exit
}
# Make the viewer and show the picture:
wm title . "Picture: $name"
image create photo p -data $data -format GIF
label .top -image p
button .quit -text Close -command exit -default active
bind . <Return> exit
pack .top -side top
pack .quit</PRE
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