[Cayenne-user] Switching databases

You probably have a few options. The DataMap part of the model could
mostly be reused. You could programatically create a DataNode (for
your DB connection) and attach it to the DataMap or you could create
the DataNode in the modeler and programatically adjust the settings in
it. As for the PKs, you'd most likely need to iterate through the
DataMap and set the PK Generation Strategy depending upon your
DataNode type (the features used by your database: auto-increment,
sequences, etc). Or, I suppose, you could use the generic
AUTO_PK_SUPPORT table that Cayenne can generate for you.

As for stored procedures ... Cayenne doesn't create/manage those for
you, but you can define how to call the procedure in the modeler.

I suspect I didn't really directly answer your questions, but perhaps
gave you a few more things to think about to ask more questions. :-)

mrg

Cayenne project mapping is close to a 100% portable between different
DB's as long as the DB's themselves are compatible. I guess the only
piece that will need to change is DataNode connection info (and this
can be delegated to container by using JNDI node).

Now specific items:

1. DbAdapter:
Analog of Hibernate's dialect in Cayenne is DbAdapter. Cayenne has
auto-detection of the DB type, so the correct DbAdapter is installed
automatically. No need to change anything.

2. PK generation:
Auto ID generation mechanism may differ between DBs. It has to be
installed on the target DB either manually before starting the app, or
with some simple Cayenne code using DbGenerator class on startup. In
any event, the differences between DB's are still abstracted and won't
require mapping changes. E.g. for Oracle DbGenerator will create PK
sequences, while for MySQL - a PK lookup table.

3. Stored procedures:
generally mappings should be portable, however different DB's may have
incompatible formats for handling in/out parameters and returned
result sets. So let's look at specific cases for me to comment more
intelligently.

Hope this helps.

Andrus

Thanks everyone. This is definitely making me feel more comfortable with
Cayenne as an ORM choice. For #2 (PK Generation) below, does that mean I
have to roll my own generator? Is there more detailed documentation on
that (don't see it on the website)?

Thanks again.
-Mike




From:
Andrus Adamchik <[email protected]>
To:
[email protected]
Date:
03/24/2010 08:16 AM
Subject:
Re: Switching databases



Cayenne project mapping is close to a 100% portable between different
DB's as long as the DB's themselves are compatible. I guess the only
piece that will need to change is DataNode connection info (and this
can be delegated to container by using JNDI node).

Now specific items:

1. DbAdapter:
Analog of Hibernate's dialect in Cayenne is DbAdapter. Cayenne has
auto-detection of the DB type, so the correct DbAdapter is installed
automatically. No need to change anything.

2. PK generation:
Auto ID generation mechanism may differ between DBs. It has to be
installed on the target DB either manually before starting the app, or
with some simple Cayenne code using DbGenerator class on startup. In
any event, the differences between DB's are still abstracted and won't
require mapping changes. E.g. for Oracle DbGenerator will create PK
sequences, while for MySQL - a PK lookup table.

3. Stored procedures:
generally mappings should be portable, however different DB's may have
incompatible formats for handling in/out parameters and returned
result sets. So let's look at specific cases for me to comment more
intelligently.

Hope this helps.

Andrus

As long as you are using one of the standard PK generation schemes
supported by Cayenne, you don't have to roll your own. If you want to
do something special, like use a GUID type column that you calculate,
then you'd have to create your own for that. I'm not sure if there is
more detailed documentation (I don't recall any), but it is fairly
simple to do now. Under the DataNode's Adapter tab in CM, you can
specify a custom DbAdapter (subclass one of the Cayenne ones) and
override the PK generator portions to use your custom PK generator. A
friend of mine fairly new to Cayenne did this in less than an hour to
generate his GUID values.

mrg