Re: 'image' table with relationships to different objects

On 2/9/2010 6:59 AM, Richard Huxton wrote:
> On 09/02/10 07:49, Louis-David Mitterrand wrote:
>> Hello,
>>
>> In my database I have different object types (person, location, event,
>> etc.) all of which can have several images attached.
>>
>> What is the best way to manage a single 'image' table with relationships
>> to (potentially) many different object types while keeping referrential
>> integrity (foreign keys)?
>
> The "clean" way to do this would be with a number of joining tables:
>
> images (img_id, file_name, title ...)
> persons (psn_id, first_name, last_name, ...)
> locations (loc_id, loc_name, lat, lon, ...)
> events (evt_id, evt_name, starts_on, ends_on, ...)
>
> person_images (psn_id, img_id)
> location_images (loc_id, img_id)
> event_images (evt_id, img_id)

Another why that reduces the number of tables and simplifies the selects
and allows linking to unlimited number of objects is something like this

is something like this
Create table images (img_id serial , img_data bytea );

Create table image_related( img_rel_id serial, img_rel_img_id int,
img_link_key int, img_link_from char(10) );

Create table persons (psn_id serial, first_name text, last_name text) ;
create table locations (loc_id serial, loc_name text) ;
create table events (evt_id serial, evt_name text, starts_on
timestamp, ends_on timestamp);

Insert into images values (default, null), (default, null), (default, null);

Insert into persons values ( default, 'me me', 'yes itsme');
Insert into locations values (default, 'I home');
Insert into events values (default, 'friends party', now(), now() );
insert into image_related values (default, 1, 1, 'persons'), (default
,2, 1, 'events'), (default ,3, 1, 'locations'), (default , 2, 1, 'persons');

Select img_data, first_name from persons, images, image_related
where img_id = img_rel_img_id
and img_link_key = psn_id
and img_link_from = 'persons'

then create a rule on img_related before insert and update to make sure
the parent records exist for integrity checks.

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