Accessing A Database - Revision history

Visitatvishal at 12:09, 17 January 2012

2012-01-17T12:09:54Z

Dossy: formatting tweaks

2005-12-02T00:38:00Z

formatting tweaks

WikiSysop: imported from WiKit id 825

2005-09-07T05:36:03Z

imported from WiKit id 825

New page

Note: This tutorial is still very incomplete as of 16aug2004.

----

This is the simplest example of how to query a database. It is not the recommended way to do it.

<%
# change "poolname" to match the pool you defined in your config.tcl
set pool "poolname"
# change to reflect the SQL you wish to execute
set sql "SELECT NOW()"

set db ""
catch {
set db [[ns_db gethandle $pool]]
set row [[ns_db select $db $sql]]
while {[[ns_db getrow $db $row]]} {
ns_adp_puts "row: [[ns_set array $row]]<br/>"
}
}
catch { ns_db releasehandle $db }
%>

Caveats:
* If you don't explicitly do an ''[ns_db releasehandle $db]'', that connection will not be returned to the pool, which can lead to accidentally exhausting all pool handles. This can easily happen if an uncaught Tcl error is thrown in code before the ''[ns_db releasehandle]'' call is made, thus causing it to never get executed.

This isn't true. All handles are released after the connection has finished processing. However, you should be aware that a db handle is a precious resource, so before you ''ns_return'' the results of your query, which may potentially take a long time, you should release your handles manually.

'''SEE ALSO'''

: [[ns_db]]

: [http://wiki.tcl.tk/13185 Introduction to Database Access With nstcl] on [http://wiki.tcl.tk/0 The Tcler's Wiki] (''the nstcl package reimplements the ns_* functions from AOLserver'')

----

[[Category Documentation]] - [[Category Tutorial]]

@@ Line 6: / Line 6: @@
 <pre>
-    <%
+  <%
-      # change "poolname" to match the pool you defined in your config.tcl
+   # set pool "postgres_pool", defined in aolserver.tcl/config.tcl
-      set pool "poolname"
+   set pool "postgres_pool"
-      # change to reflect the SQL you wish to execute
+   set sql "select * from users"
-      set sql "SELECT NOW()"
+   set db [ns_db gethandle $pool]
+   set row [ns_db select $db $sql]
-      set db ""
+   while {[ns_db getrow $db $row]} {
-      catch {
+    ns_adp_puts "row: [ns_set array $row]"
-        set db [ns_db gethandle $pool]
-        set row [ns_db select $db $sql]
+   ns_db releasehandle $db
-        while {[ns_db getrow $db $row]} {
+ %>
 </pre>

@@ Line 1: / Line 1: @@
-Note:  This tutorial is still very incomplete as of 16aug2004.
+: ''Note:  This tutorial is still very incomplete as of 16aug2004.''
 ----
@@ Line 5: / Line 5: @@
 This is the simplest example of how to query a database.  It is not the recommended way to do it.
      <%
        # change "poolname" to match the pool you defined in your config.tcl
@@ Line 13: / Line 14: @@
        set db ""
        catch {
-         set db [[ns_db gethandle $pool]]
+         set db [ns_db gethandle $pool]
-         set row [[ns_db select $db $sql]]
+         set row [ns_db select $db $sql]
-         while {[[ns_db getrow $db $row]]} {
+         while {[ns_db getrow $db $row]} {
-           ns_adp_puts "row: [[ns_set array $row]]<br/>"
+           ns_adp_puts "row: [ns_set array $row]<br/>"
+         }
+       }
        catch { ns_db releasehandle $db }
      %>
 * If you don't explicitly do an ''[ns_db releasehandle $db]'', that connection will not be returned to the pool, which can lead to accidentally exhausting all pool handles.  This can easily happen if an uncaught Tcl error is thrown in code before the ''[ns_db releasehandle]'' call is made, thus causing it to never get executed.
 This isn't true.  All handles are released after the connection has finished processing.  However, you should be aware that a db handle is a precious resource, so before you ''ns_return'' the results of your query, which may potentially take a long time, you should release your handles manually.
-'''SEE ALSO'''
+== See also ==
-----
+: [[ns_db]], [http://wiki.tcl.tk/13185 Introduction to Database Access With nstcl] on [http://wiki.tcl.tk/ The Tcler's Wiki] ''(the nstcl package reimplements the ns_* functions from AOLserver)''
-[[Category Documentation]] - [[Category Tutorial]]
+[[Category:Documentation]]