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From Jan Marten Visser <jan.marten.vis...@virgil.nl>
Subject Re: Database schema changes: migration how to
Date Thu, 27 Mar 2003 16:23:42 GMT

Eric Emminger wrote:
> Max
> > I'm evaluating possibility on using an O-R mapping tool in my current
> > project.  I've read tutorial on torque and similar other O-R mapping tools and
> > wonder how the migration is managed.
> >
> > Suppose, I've created a book database scheme, generate sql/java code and
> > deploy it. Some time later when a lot of data 's been filled into DB I
> > discovered that I had to add/change/remove some properties on the Book
> > class. I could tweak the schema file and re-create sql/java code but how
> > one typically perform migration data to new db scheme.
> >
> > An elaborate answer or pointers to relevant Web resources are greatly
> > appreciated.
> As far as I know, no OR mapping tool, including Torque, has an easy way
> to migrate data between changed models. Migration usually involves
> either database-specific SQL code to change the existing database, or
> creating a new database and moving the data.
> If you know or find anything that would change the above information,
> please tell us, or at least me. :)

I guess I am missing the point here, if you change a relational database
scheme, e.g. add columns, you introduce new data. It is off course
impossible to generate new data by means of Torque or any tool.
I guess you are referring to other changes.

Could you give an example of such a change which could be supported by
tools because I think I am missing the point.

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