Hi,
ABOU LINA wrote:
Hi,
ok so, i made DAO implementation with OJB PB in a critical project and we
are in step of delivring some module of the application (the mainly module
now are developped and tested). my question is :
1. what will be the cost of migrating from PB to ODMG. ???
There is no need to completely migrate to ODMG.
For all read-only operations the PB-api can still be used without
modification.
For all insert/update/delete operations use the ODMG-api. Anyway it is
possible to use the PB-api within the odmg-api, so there is no need to
use OQL-queries within odmg-tx
http://db.apache.org/ojb/docu/guides/odmg-guide.html#Access+the+PB-api+within+ODMG
All objects read by the PB instance have to be locked *before* you start
to modify these objects.
http://db.apache.org/ojb/docu/guides/odmg-guide.html#I+don%27t+like+OQL%2C+can+I+use+the+PersistenceBroker+Queries+within+ODMG
When using OQL-queries by default OJB lock all received objects, see
'implicit locking' section
http://db.apache.org/ojb/docu/guides/odmg-guide.html#Configuration+Properties
http://db.apache.org/ojb/docu/guides/odmg-guide.html#The+TransactionExt+Interface
But take care not to use PB instances looked up from the PBF within a
odmg-tx.
2. there are some tools making this migration easy and fast ???
Sorry, there is no tool. But in the metadata files you only have to
change the auto-xxx settings of your references
http://db.apache.org/ojb/docu/guides/odmg-guide.html#Specific+Metadata+Settings
3. in your opinion, the probleme about deleting collection elements justify
using ODMG instead of PB ???
This depends on your requirements. If you need this behavior
>>> we don't
>>> invoke remove but we construct a new collection and we set it :
>>> 1. get A from database.
>>> 2. Collection bCol = new ArrayList();
>>> A.setBCollection(bCol);
then you have to use the odmg-api.
4. Best practice of ODMG and good examples ??
Have a look in the ODMG tutorial, the odmg-guide and in OJB's test-suite
classes for the ODMG-api.
http://db.apache.org/ojb/docu/tutorials/odmg-tutorial.html
http://svn.apache.org/viewcvs.cgi/db/ojb/branches/OJB_1_0_RELEASE/src/test/org/apache/ojb/odmg/?rev=378044
Sorry, best practice is missing.
regards,
Armin
Thanks.
On 3/9/06, Armin Waibel <[EMAIL PROTECTED]> wrote:
Hi,
ABOU LINA wrote:
thank first,
PersistenceBroker *delete elements* from the database that have been
removed
from the collection only if i do this :
for example : A 1:n B
1. i get A from database using OJB Broker.
2. i delete one element B from A : A.getBCollection().remove(o);
in this case yes the PB delete the element from database . but in
generale
we don't
invoke remove but we construct a new collection and we set it :
1. get A from database.
2. Collection bCol = new ArrayList();
A.setBCollection(bCol);
in this case the element that not figure in bCol are not deleted because
i
use ArrayList. (in my Application i can't put RemovalAwareList directly
There is no need to handle with RemovalAwareList instances in your
POJO's. Using type 'List' is sufficient and on insert of new objects you
can use ArrayList, so
2. Collection bCol = new ArrayList();
A.setBCollection(bCol);
is valid when insert new objects.
But you are right, when updating objects you have to use
Collection.remove(...) method.
2. i delete one element B from A : A.getBCollection().remove(o);
it's not allowed to replace the old List with a sub-List instance.
inorder to keep the application independent of OJB classes ...)
so what is the solution please ... without using ODMG ?????
There is none.
That's the main difference between the PB-api and ODMG. The ODMG
implementation use a "Unit of work" pattern (object state detection,
detection of new/deleted objects) the PB-api does immediately write
objects to DB and does not keep the objects state "in mind".
For the next major release of OJB we plan to extend the PB-api to
support a "unit of work" pattern with locking.
regards,
Armin
Thanks
On 3/7/06, Armin Waibel <[EMAIL PROTECTED]> wrote:
Hi,
ABOU LINA wrote:
Hi,
in ojb document :
---------------------------------------
Say you use the PB to query an object O that has a collection
attribute
col
with five
elements a,b,c,d,e. Next you delete Objects d and e from col and store
O
again with
PersistenceBroker.store(O);
PB will store the remaining objects a,b,c. But it will not delete d
and
e !
If you then
requery object O it will again contain a,b,c,d,e !!!
--------------------
i ask if the new version of PB (1.0.4) still behave like this ???
Oops! Seems you found some outdated documentation - I will fix this
till
next release.
With corresponding settings OJB 1.0.4 is able to detect the deleted
objects of the 1:n reference. More info see
http://db.apache.org/ojb/docu/guides/basic-technique.html#1%3An+auto-xxx+setting
http://db.apache.org/ojb/docu/guides/advanced-technique.html#which-collection-type
regards,
Armin
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