Setting Up Database Objects

by Joel Aufrecht

OpenACS docs are written by the named authors, and may be edited by OpenACS documentation staff.

Code the data model

We 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 PostgreSQL

The 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.)

Figure 9.2. Tutorial Data Model

Tutorial Data Model

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.sql

Paste the text below into the file, save, and close.

Figure 9.3. The Database Creation Script

-- creation script
--
-- @author joel@aufrecht.org
-- @cvs-id &Id:$
--

select content_type__create_type(
    'mfp_note',                    -- content_type
    'content_revision',            -- supertype
    'MFP Note',                    -- pretty_name,
    'MFP Notes',                   -- pretty_plural
    'mfp_notes',                   -- table_name
    'note_id',                     -- id_column
    null                           -- name_method
);

-- necessary to work around limitation of content repository:
select content_folder__register_content_type(-100,'mfp_note','t');

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

Figure 9.4. Database Deletion Script

-- drop script
--
-- @author joel@aufrecht.org
-- @cvs-id &Id:$
--
select content_folder__unregister_content_type(-100,'mfp_note','t');

select content_type__drop_type(
           'mfp_note',
           't',
           't'
    );

(like the creation script the drop script calls a PL/pgSQL function: content_type__drop_type

Run 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