Re: Dynamically generating DDL for postgresql object

Thanks, John. This is very helpful in getting me on the right track. The
pg_get_constraintdef(oid) function seems to provide what's needed to
recreate the constraint. Interestingly, it doesn't include some of the
information displayed in pgAdmin (i.e. Match type, On Update, On Delete) -
perhaps these property values will be easy to "guess" when recreating the
constraint. Example below ...

Thank you again, John. Cheers, Mark

Example:

Case 1: pg_get_constraintdef(oid) output:

"FOREIGN KEY (permission_id) REFERENCES auth_permission(id) DEFERRABLE
INITIALLY DEFERRED"

Caset 2: pgAdmin SQL pane display

ALTER TABLE auth_group_permissions
ADD CONSTRAINT auth_group_permissions_permission_id_fkey FOREIGN KEY
(permission_id)
REFERENCES auth_permission (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION DEFERRABLE INITIALLY DEFERRED;

-----------------------
Mark Soper
markasoper(at)hotmail(dot)com
25 Fairmont St #2
Cambridge, MA 02139
(617) 491-4134

-----Original Message-----
From: John DeSoi [mailto:desoi(at)pgedit(dot)com]
Sent: Friday, June 15, 2007 9:51 PM
To: Mark Soper
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: [GENERAL] Dynamically generating DDL for postgresql object

On Jun 15, 2007, at 2:31 PM, Mark Soper wrote:

> I'd like to dynamically generate a SQL script that pulls together
> complete DDL (CREATE, ALTER, etc.) for specific objects (especially
> constraints) in my PostgreSQL 8 database. I want to use this for
> our development project's schema migration process, which involves
> dumping the data, making schema changes, recreating the database,
> temporarily removing constraints, restoring the data, and re-
> applying the constraints (this last step requires the dynamic DDL
> described above).
>
>
>
> I've noticed that pgAdmin's "DDL Report" feature can retrieve this
> DDL for many types of objects - not sure how much work it has to do
> to build the SQL it's displaying here. But I haven't seen anything
> about getting this directly from the database using SQL , psql,
> etc. I've only seen reference to this as a proposed project on the
> PostgreSQL Google SoC page
>
>
>
> Anyone know how to get object DDL SQL through a script? Ideas on
> alternative approaches would also be appreciated.

There are a number of built-in functions for getting the SQL DDL, but
it depends on the version you are using. Here is what I see for 8.2:

=== psql 1 ===

\df pg_get*

List of functions
Schema | Name | Result data type | Argument
data types
------------+------------------------+------------------
+-----------------------
pg_catalog | pg_get_constraintdef | text | oid
pg_catalog | pg_get_constraintdef | text | oid, boolean
pg_catalog | pg_get_expr | text | text, oid
pg_catalog | pg_get_expr | text | text, oid,
boolean
pg_catalog | pg_get_indexdef | text | oid
pg_catalog | pg_get_indexdef | text | oid,
integer, boolean
pg_catalog | pg_get_ruledef | text | oid
pg_catalog | pg_get_ruledef | text | oid, boolean
pg_catalog | pg_get_serial_sequence | text | text, text
pg_catalog | pg_get_triggerdef | text | oid
pg_catalog | pg_get_userbyid | name | oid
pg_catalog | pg_get_viewdef | text | oid
pg_catalog | pg_get_viewdef | text | oid, boolean
pg_catalog | pg_get_viewdef | text | text
pg_catalog | pg_get_viewdef | text | text, boolean
(15 rows)

For example, if you know the table oid, you can get the constraint
definitions with something like this:

select 'CONSTRAINT ' || conname || ' ' || pg_get_constraintdef(oid)
|| ';' as condef
from pg_constraint where conrelid = oidxyz;

Getting the full DDL for a table requires a lot more work using the
system catalogs. See pg_dump for hints.

John DeSoi, Ph.D.
http://pgedit.com/
Power Tools for PostgreSQL