In this node: Re: Class::DBI Intro, dbwiz had the following to say in response to a tutorial Class::DBI Intro:

The delete method is rather inefficient. When called, Class::DBI will issue one DELETE statement for each row in your table. Instead of producing

DELETE FROM page WHERE user_id = 1
DELETE FROM user WHERE user_id = 1
[download]

It does

DELETE FROM   page WHERE  page_id = '1'
DELETE FROM   page WHERE  page_id = '2'
DELETE FROM   page WHERE  page_id = '3'
DELETE FROM   page WHERE  page_id = '4'
DELETE FROM   page WHERE  page_id = '5'
DELETE FROM   user WHERE  user_id = '1'
[download]

which can be quite long for large data sets. The sad thing is that, even if I use a database that enforces referential integrity, Class::DBI will still override the database features and issue the same DELETE statements. In your example, if you replace the table definition to use the InnoDB table type, adding

FOREIGN KEY (user_id) references user (user_id) ON DELETE CASCADE,
KEY user_id (user_id)
# and replace "MyISAM" with "InnoDB" for both tables
[download]

You can then get the same behavior with

%dbh->do("DELETE FROM user WHERE user_id=1")
[download]

and the database engine will take care of cascade deletiing the appropriate records in "page".

This is where I got my info from. The suggestion is obviously that Class::DBI will issue a series of deletes inefficiently over-riding the ON DELETE constraint. I haven't tried it yet, but from my reading you are correct about the INSERT and UPDATE constraints.

I would value your comments on the DELETE case as well!

jdtoronto
PS Do you know of any examples I could look at of multi-table JOIN's in Class::DBI? ..j

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