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-boun...@postgis.refractions.net [mailto:postgis-users-boun...@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:l...@pcorp.us> To: 'PostGIS Users <mailto:postgis-users@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-boun...@postgis.refractions.net [mailto:postgis-users-boun...@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 _____ _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
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