Hi Terrence,
Sorry for not replying earlier ... lots of things on Cayenne front
plus the holidays :-)
Re: ObjectId question:
Putting PK values in the map returned by 'getReplacementIdMap' is
guaranteed to get picked up by Cayenne on commit and processed
properly. If you change the ObjectId by hand, the behavior is
unpredictable, as the ObjectId is used as a key in the internal cache
maps. In fact it may vary between different versions of Cayenne (I
think we did catch manual ObjectId changes before, but I can't locate
this code in 3.0 anymore... may still be there, just that I forgot
where it was).
But an official way to install a custom PkGenerator is by implementing
your own org.apache.cayenne.dba.PkGenerator. The generator should
only implement the 'generatePkForDbEntity' and 'reset' methods. The
rest can simply throw "UnsupportedOperationException" as they are not
called in runtime. There are a few ways to install custom PkGenerator:
* Cast runtime DbAdapter to JdbcAdapter or AutoAdapter as appropriate
and call "setPkGenerator()"
* Subclass OracleAdapter, overriding 'JdbcAdapter.createPkGenerator()'
method, and entering the name of your adapter for DataNode in the
Modeler.
As Ari mentioned, your solution (as well as 'getReplacementIdMap'
solution) has a race condition (that may or may not be relevant in
your environment). Consider that between the time you obtain a PK with
a query and a commit, another thread/process can attempt an insert and
get the same id. As a result one of the two commits will fail with a
duplicate PK SQL exception (or much worse - go through if the
constraint is not defined on oracle, resulting in corrupt data).
PkGenerator solution is less prone to a race condition, as it is done
in the same JDBC transaction as the main commit, however it also
depends on how you implement it (SELECT ... FOR UPDATE may be needed
here).
Hope this helps.
Andrus
On Dec 27, 2007, at 4:46 PM, Terrence A. Pietrondi wrote:
Any feedback on this topic? I read the mentioned
"Handling Inheritance" article, if I shouldn't use the
table names, how can I check for my category concepts
as I mentioned? Since there are multiple tables that
are the categories.
I am a little unclear how using
ObjectId.getReplacementIdMap().put(...) might help as
mentioned in an earlier post. Is there any other
information I can better provide to better explain my
approach. How is this safer then using my own ObjectId
object and settings its id?
Thanks.
--- "Terrence A. Pietrondi" <[EMAIL PROTECTED]>
wrote:
--- Aristedes Maniatis <[EMAIL PROTECTED]> wrote:
The simplest way to have Cayenne handle PK
generation is to follow the
instructions here:
http://cayenne.apache.org/doc/generate-primary-key-support.html
That will implement a solution which is thread
safe
and portable
between databases. I don't believe your solution
would be thread safe.
Here is the trick, the work I am doing is on an
existing database (Oracle) and I do not have access
to
modify the existing schema. It could be possible
that
I go through a review with our database developer,
but
I am trying to solve the problem within the
constrains
of his design. For whatever reason, he chose not to
implement auto-key generation and is expecting that
to
take place in the application code. Whether that is
a
good design decision or not is arguable, but I'd
like
to continue the implementation of my solution
without
database modifications. And therefore, key
generation
is going to have to take place in the application
code. Hope that is not too confusing.
What is it you are wanting to do here? One of the
primary purposes of
an ORM is to insulate the user from the database
schema, allowing you
to refactor the database naming and schema without
touching your Java
code. Hardcoding in database field names may not
be
in the best
interests of this approach. Also the comments in
your example suggest
a one to one mapping between databases tables
(DbEntity) and
ObjEntity. This is not always true in Cayenne:
http://cayenne.apache.org/doc/handling-inheritance.html
I have a service that has a method to set a value
for
an entry of a member on a table. This method is
"annotating" a "member" of a "category"
(conceptually). And so, when using the "annotate"
method, of the arguments for this method are a
"rule"
and a "value". A "rule" is a column on the database
table, and a table represents a "category". I need
to
map this "rule" to the correct property name in
Cayenne so I can set it properly for the correct
"member". To be clear, I am editing an existing
entry
in the table, but I am targeting a specific column
to
set, and I need to map from the column name to the
property name.
Thanks.
Terrence A. Pietrondi
http://del.icio.us/tepietrondi
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