[odb-users] Generating Database Support Code

Boris Kolpackov boris at codesynthesis.com
Tue Dec 14 10:58:46 EST 2010

Hi Myoungkyu,

I've CC'ed my reply to the odb-users mailing list since others might
have similar questions.

Myoungkyu Song <mksong at vt.edu> writes:

> I wanted to give you some background about my research project.

Thanks, sounds very interesting.

> I was wondering if pragmas is the only means of interfacing with the ODB
> compiler. In our case, we need to add pragmas to the C++ files emitted by
> the X10 to C++ compiler, which may require us to modify the compiler making
> it aware of the persistent classes.
> Is it possible to specify persistent C++ classes using a configuration file
> or an XML deployment descriptor? In other words, even though pragmas are
> pretty straightforward to add, this requires parsing C++ header files, so I
> was wondering if this can be somehow avoided. 

Pragmas can be factored out to a separate file which would be more or
less the "mapping" file you are looking for. For instance, the pragmas
in the 'hello' example can be rewritten like this:

// file      : hello/person-mapping.hxx

#pragma db object(person)
#pragma db member(person::id_) id auto

In ODB 1.0.0 you would still need to #include this file at the end of 
the header file that defines the persistent classes. For example:

// file      : hello/person.hxx


#  include "person-mapping.hxx"

In the upcoming ODB 1.1.0 the header file can be left unchanged and the
mapping file added to the ODB compilation process with the --odb-prologue
compiler option.

For more information, see Chapter 5, "ODB Pragma Language", particularly
the next on named pragmas:


> I was also wondering whether it is possible to persist a subset of the
> fields of a persistent class. In other words, is it possible to configure
> ODB in such a way that some of the fields remain transient?

Yes, you can mark any member as transient with the 'transient' pragma.
Again, see the documentation for details.


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