On 28 Feb 2008, at 09:51, Dermot wrote:
1) I have been using the MySQL workbench tool to try and make a ER
diagram of a database. The community edition doesn't allow printing
but is excellent in every other way. Could anyone recommend a
similar tool? I hear Dia is a good OS tool.
Given a db or DBIC description, there are some tools in
SQL::Translator to spit out ER diagrams.
2) I posted a query about the Catalyst tutorials and that fact that
the used a join table to show many to many relationships between
authors and books. Is this type of table what is termed a view? Or
am I still not getting it :-(
Not a view - those are the table like things you can produce with
CREATE VIEW ...
The problem is that you can do a many-to-one or one-to-many
relationship by having the many item contain a foreign key to the one
item. However there is no such neat method to do a many-to-many
relationship, so you have to break it down to be a pair of
relationships - a many-to-one-to-many combination with the link table
in the middle consisting of foreign keys to the other pair of tables.
As an example, for a theatre event (as in show) handling db I have,
each show has 0 or more ticket agencies selling tickets. The ticket
agencies are re-used for many events (so a place in town will sell
tickets for many events).
Hence I have an "event" table
and a "ticket_agent" table
and a "event_ticket_agent" table - this one purely consists of 2
fields - the event id and the ticket_agent id, and links the pair.
I refer to that as a link table, but I am a sysadmin rather than a DB
expert :-)
Hope that helps a bit.
Nigel.
--
[ Nigel Metheringham [EMAIL PROTECTED] ]
[ - Comments in this message are my own and not ITO opinion/policy - ]
_______________________________________________
List: http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbix-class
IRC: irc.perl.org#dbix-class
SVN: http://dev.catalyst.perl.org/repos/bast/DBIx-Class/
Searchable Archive: http://www.grokbase.com/group/[EMAIL PROTECTED]
