[postgis-users] Loop or Cursor

[Paragon Corporation]

Bob,
 
For this kind of thing -- we usually use a database trigger on the AFTER
INSERT row event of the table in question.  You would also probably need an
AFTER UPDATE trigger as well since as a child object is being updated,
you may want to update the parent if the update condition affects the
structure/position of the parent.  So in essence you would have  a RECURSIVE
trigger that keeps on recursing until the final has no parents.  Though
you'd need to be careful to make sure you don't have cyclical redudancies
that could trigger an infinite recursion.
 
Perhaps if you provided the update statement you are trying to run we could
be of more help.
 
Leo

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Pawley
Sent: Tuesday, July 21, 2009 11:19 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Loop or Cursor


Hi Leo
 
I'm developing a geometric system as opposed to geographic (basically an
engineering drawing).
 
I have a fixed field, representing a peice of paper, within which the user
can add one to four objects.
 
These object are placed within the field according to the total number of
objects.
 
The first object 'A' is placed in the center and then the user adds lines
(one to eight at the moment) as attributes to the object.
 
When the user adds a second object, I want to update the attributes of
object A to satisfy the new placement of object A.
 
When the user places a third object then both, object A and B, need to be
updated.
 
At the moment, my updates haven't worked as I get  either a null or multiple
return.
 
Any suggestions for updating the lines for each object would be greatly
appreciated.
 
Thanks
 
Bob
 
 

----- Original Message ----- 
From: Paragon Corporation <mailto:lr at pcorp.us>  
To: 'PostGIS Users  <mailto:postgis-users at postgis.refractions.net>
Discussion' 
Sent: Monday, July 20, 2009 7:45 PM
Subject: Re: [postgis-users] Loop or Cursor

What kind of operation?  Even an update statement might suffice.  There are
many ways to cleverly control the flow of an update that do not necessitate
doing a loop or cursor.
 
Also keep in mind even within a function used in a  SELECT statement of a
query, PostgreSQL allows you to run updates and do all sorts of crazy things
like launch perl scripts and bash scripts.  So for example you can mail to
your whole membership simple by doing this
 
SELECT member_name, send_mail(member_id) As did_it_send
FROM membership
WHERE gross_income > 1000000 and active = true
 
 
It is very convenient for making rule processors.
 
Leo
 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Pawley
Sent: Monday, July 20, 2009 1:43 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Loop or Cursor


Hi
 
I need to access a number of rows, one at a time to perform an operation on
each.
 
Under what conditions would I consider using a loop command, rather than (or
with) a cursor?
 
Bob



  _____  




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