Setting Up Database Objectsby Joel AufrechtCode the data modelWe create all database objects with scripts in the
myfirstpackage/sql/ directory. All
database scripts are database-specific and are thus in either
the myfirstpackage/sql/oracle or
myfirstpackage/sql/postgresql directory.
Packages can support Oracle, PostgreSQL, or both. In this
tutorial, we will be working with PostgreSQLThe first file will be
myfirstpackage-create.sql. The
package manager requires a file with the name
packagekey-create.sql,
which it will run automatically when the package in installed.
This file should create all tables and views.Our package is going to store all of its information in
one table. It takes more than just a CREATE
TABLE command, however, because we want to
integrate our table with the OpenACS system. By making each
record in our table an OpenACS object, we gain access to the
permissions system and to services that integrate with OpenACS
objects, such as general-comments and
notification. The cost is
that our table creation code must include several functions,
stored procedures, and is complicated (even for simple tables).There are many kinds of OpenACS objects in the system. (You
can see them with the psql code: select object_type from
acs_object_types;.) One such object is the
content_item, which is part of the content repository system.
To use it, we will make our data objects children of the content_revision object,
which is a child of content_item. Not only will we gain the benefits of both OpenACS
Objects and content objects, we can also use some content
repository functions to simplify our database creation. (More
information about ACS Objects. More information about the
Content Repository.)
The top of each sql file has some
standard comments, including doc tags such as
@author which will be picked up
by the API browser. The string
$Id:$ will automatically be
expanded when the file is checked in to cvs.[$OPENACS_SERVICE_NAME ~]$ cd /var/lib/aolserver/$OPENACS_SERVICE_NAME/packages/myfirstpackage/sql/postgresql
[$OPENACS_SERVICE_NAME postgresql]$ emacs myfirstpackage-create.sqlPaste the text below into the file, save, and close.The creation script calls a function in PL/pgSQL (PL/pgSQL is a procedural language extension to sql),
content_type__create_type, which
in turn creates the necessary database changes to support our data
object. Notice the use of "mfp." This is derived from "My
First Package" and ensures that our object is unlikely to conflict
with objects from other packages.Create a database file to drop everything if the package is uninstalled.
[$OPENACS_SERVICE_NAME postgresql]$ emacs myfirstpackage-drop.sql(like the creation script the drop script calls a PL/pgSQL function: content_type__drop_typeRun the create script manually to add your tables and functions.[$OPENACS_SERVICE_NAME postgresql]$ psql service0 -f myfirstpackage-create.sql
psql:myfirstpackage-create.sql:15: NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index 'mfp_notes_pkey' for table 'mfp_notes'
psql:myfirstpackage-create.sql:15: NOTICE: CREATE TABLE will create implicit trigger(s) for FOREIGN KEY check(s)
content_type__create_type
---------------------------
0
(1 row)
[$OPENACS_SERVICE_NAME postgresql]$If there are errors, use them to debug the sql file and try again. If there are errors in the database table creation, you may need to run the drop script to drop the table so that you can recreate it. The drop script will probably have errors since some of the things it's trying to drop may be missing. They can be ignored.Once you get the same output as shown above, test the drop script:[$OPENACS_SERVICE_NAME postgresql]$ psql service0 -f myfirstpackage-drop.sql
content_type__drop_type
-------------------------
0
(1 row)
[$OPENACS_SERVICE_NAME postgresql]$Once both scripts are working without errors, run the create script one last time and proceed.[$OPENACS_SERVICE_NAME postgresql]$ psql service0 -f myfirstpackage-create.sql