Calendar

part of the ArsDigita Community System by Philip Greenspun

The Big Idea

A site like photo.net might want to offer a calendar of upcoming events. This has nothing to do with displaying things in a wall-calendar style format, as provided by the calendar widget. In fact, a calendar of upcoming events is usually better presented as a list.

What distinguishes /calendar from /news is that items may be categorized and the display at a large site might be personalized to a user's country, state, or zip code. Also, if there are too many items to display comfortably, the non-expired events coming up soonest get displayed.

See www.harpcolumn.com for a good running example that distinguishes /news from /calendar.

Under the Hood

The data model is simple: 



create sequence calendar_category_id_sequence start with 1 ;

create table calendar_categories (
        category_id     integer primary key,
        -- if scope=public, this is the address book the whole system
        -- if scope=group, this is the address book for a particular group
        scope           varchar(20) not null,
        group_id        references user_groups,
        category        varchar(100) not null,
        enabled_p       char(1) default 't' check(enabled_p in ('t','f')),
        constraint calendar_category_scope_check check ((scope='group' and group_id is not null) or
                                                        (scope='public')),
        constraint calendar_category_unique_check unique(scope, category, group_id)     
);

create index calendar_categories_group_idx on calendar_categories ( group_id );

create sequence calendar_id_sequence start with 1;

create table calendar (
        calendar_id     integer primary key,
        category_id     not null references calendar_categories,
        title           varchar(100) not null,
        body            varchar(4000) not null,
        -- is the body in HTML or plain text (the default)
        html_p                  char(1) default 'f' check(html_p in ('t','f')),
        start_date      date not null,  -- first day of the event
        end_date        date not null,  -- last day of the event (same as start_date for single-day events)
        expiration_date date not null,  -- day to stop including the event in calendars, typically end_date
        event_url       varchar(200),  -- URL to the event
        event_email     varchar(100),  -- email address for the event
        -- for events that have a geographical location
        country_code    references country_codes(iso),
        -- within the US
        usps_abbrev     references states,
        -- we only want five digits
        zip_code        varchar(10),
        approved_p      char(1) default 'f' check(approved_p in ('t','f')),
        creation_date   date not null,
        creation_user           not null references users(user_id),
        creation_ip_address     varchar(50) not null
);
Comments are handled by the general comments facility.

Related Modules

The /news module is better for generation announcements (e.g., press releases from companies).

The /bboard system is better if you want to support lively discussion and archive the exchanges.