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SOLVED - Re: Dynamic sql and variable record types

From: Erik Jones <erik(at)myemma(dot)com>
To: Erik Jones <erik(at)myemma(dot)com>
Cc: SQL Postgresql List <pgsql-sql(at)postgresql(dot)org>
Subject: SOLVED - Re: Dynamic sql and variable record types
Date: 2008-03-21 16:21:12
Message-ID: E2DCA422-9214-40AB-8354-CC4FA6050601@myemma.com (view raw or flat)
Thread:
Lists: pgsql-sql
On Mar 20, 2008, at 5:28 PM, Erik Jones wrote:

> Hi, I've been working on a generic date partitioning system and I  
> think I've reached something that can't be done, but I thought I'd  
> post a question to the masses in the hope that I'm missing  
> something.  The basic idea of what I'm doing is some userland  
> scripts that will accept a table name argument along with the name  
> of a date/timestamp attribute to partition on and create partitions  
> for that table along with the appropriate trigger and trigger  
> function.  The part I'm having trouble with is the trigger function.
>
> What I'm done for that is to create a template file that my scripts  
> read in and substitute the table column names wherever necessary,  
> then run the results through the db to create the functions.  The  
> problem is that for the function to be generic it needs to be able  
> to work with different record/row types.  Here's the template for  
> function (not working, which I'll discuss below):
>
> CREATE OR REPLACE FUNCTION %s_ins_func(op text, rec %s)
>    RETURNS boolean AS $$
> DECLARE
>    partition varchar;
>    name_parts varchar[];
>    upper_dim integer;
> BEGIN
>    FOR partition IN
>        SELECT relname
>        FROM pg_class
>        WHERE relname ~ ('^%s_[0-9]{8}_[0-9]{8}$')
>    LOOP
>        name_parts := string_to_array(partition, '_');
>        upper_dim := array_upper(name_parts, 1);
>        IF rec.%s >= name_parts[upper_dim-1]::timestamp AND rec.%s <  
> name_parts[upper_dim] THEN
>            IF op = 'INSERT' THEN
>                EXECUTE 'INSERT INTO %s_' || name_parts[upper_dim-1]  
> || '_' ||
>                            name_parts[upper_dim] || ' VALUES ' ||  
> rec || ';'; -- the problem is here with rec
>                RETURN TRUE;
>            END IF;
>        END IF;
>    END LOOP;
>    RETURN FALSE;
> END;
> $$ language plpgsql;
>
> The userland scripts substitute the table and column names for the  
> %s escapes where appropriate.  What the function actually does is to  
> us the parent table's name to find all of the child partitions which  
> are name like some_table_20080101_20080201, split out the dates from  
> those to determine which table the insert needs to be redirected  
> to.  That works fine.  The problem is that since I have to  
> dynamically generate the destination table name I have to use  
> EXECUTE for the INSERT statement.  But, I can't see how to use a  
> record in query passed to EXECUTE.  Am I right in thinking (now)  
> that this can't be done?

I solved this by doing a lookup of the table's attributes and putting  
them directly into the function during the templating step.

Erik Jones

DBA | Emma®
erik(at)myemma(dot)com
800.595.4401 or 615.292.5888
615.292.0777 (fax)

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