Hi Sinisa. Thanks for your answer. I understand the concept fairly well.
The doubt I had was if there was any known problem with using
deletecascade on PostgreSQL (because it is set to false by default on
the DODS installation). For what you told me, I believe there isn't any
problem.
However, with your explanation, I have now another doubt: in runtime
where do I say that deletecascade is supported by postgres? Is it on the
config file for each application (I couldn't find anything on the DODS
docs for this)? The PostgreSQLConf.xml should also be present on the
deploy environment?
Regards,
Ricardo
Sinisa Milosevic wrote:
Hi,
Some notes regarding delete cascade option in DODS. I hope it helps.
The class <table_name>DO.java (DODS generated) provides java code for
cascade delete of DOs.
In dbVendorConf files there is a parameter
<DeleteCascade>true</DeleteCascade>
If this parameter is set to true it means that sql that handles delete
cascade will be generated. The java code in <table_name>DO.java class is
always generated. When delete cascade happens, if this parameter is set to
true, sql code is executed (db will delete references), the java code (in
DODS generated classes) is not executed, and the cascade deleted DOs are
marked as deleted.
If DeleteCascade is set to false, the sql code is neither generated, nor
executed. The java code (DODS generated classes) will be executed, and
cascade references are deleted, using DODS.
But if you generate sql stataments (using DODS) with DeleteCascade = false,
and during runtime change DeleteCascade = true, your application should
delete DO's references because DODS will not delete references
(DeleteCascade = true, it means db will delete them) and db will not delete
(because sql scripts for delete cascading are not created, DeleteCascade =
true).
Regards,
Sinisa
----- Original Message -----
From: "Ricardo Tedim" <rjtedim@xxxxxxxxxxxx>
To: <enhydra@xxxxxxxxxxxxx>; <dods@xxxxxxxxxxxxx>
Sent: Wednesday, July 13, 2005 4:44 PM
Subject: [enhydra] DeleteCascade on PostgreSQL
Hi,
I'm doing some perfomance tests in a project running on top of the new
Enhydra 6.4.1 (Tomcat version) and a PostgreSQL DB engine (7.3.9). I've
noticed that on the DODS configuration that was installed with this
Enhydra, the DeleteCascade parameter for PostgreSQL is set to false.
This means that the DB reference integrity will be guaranteed by the
data layer generated by DODS, and for what I understood this is done by
fetching (on DB) the objects that have references to the object being
changed, and performing on them the required changes (if needed). So for
instance if I have a DO named A that references B and I try to delete B
using the DODS layer, this will result in following SQL operations:
1. Select B from DB and then delete it by invoking the delete method on
its DO.
2. Select A from DB (triggered by DODS)
3. Delete A and B from DB.
If this integrity is guaranteed by the DB engine, the 2nd operation and
part of the 3rd will be automatically performed by the DB engine
resulting in a performance improvement. This is what I wanted to explore
in the project I'm in, but first I would like to know from you if
there's any known issue related to the setting of this parameter to true
(since by default it is setted to false).
Thanks in advance,
Ricardo Tedim
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