Re: [Beankeeper-discussion] Schema changes

[Brautigam R. <de...@ne...>]

Shay Matasaro írta:
> Hi,
> 
> how does BeanKeepr handle schema changes(or to be exact class structure 
> changes)?
> what happens when a field is removed?
>
> what happens when a filed is added?
>
> are the table dropped in those cases?

Currently BeanKeeper has a wired-in schema evolution algorithm to handle
some simple cases. It does basically this:
- class added: table is created
- 1 field added: table is not dropped, field is added with default value
for existing objects (usually null or 0)
- 1 field is removed: table is not dropped, only if there are no other
fields
- 1 field renamed or type changed: handled as 1 removed, 1 added

For more complex changes (like added a subclass, or class hierachy
changed otherwise) a migration is probably necessary. Currently there is
not automation or helper scripts for this unfortunately.

> i am seeing the following messages in my log file :
> 
> "could not find class (data.VReseller) to table: data_vreseller. This 
> may only mean that a class was removed, but there are traces in the 
> database for it, in this case, you may disregard this message: 
> data.VReseller (java.lang.ClassNotFoundException)"
> what is the cause for these?

On startup BeanKeeper consults the database for classes that were used
on that database anytime in the past. It tries to see if those classes
are ok or not. This message indicates, that at one point in time there
were data.VReseller objects stored, but that class is currently not
available to the system, so that table will not be used. This is Ok if
you really removed that class.

> i also see this error in the logs :
> "returning empty result list because of non-fatal symbol error. Parser 
> said: could not find class for table name: vreseller, statement was: 
> find vreseller where VReseller.domain=?"
> 
> altghou i can see the table vreseller in the DB?

This means that no known class matching VReseller is being used in the
database. If the previous ClassNotFoundException is for the same class,
this would mean, either the class data.VReseller is really not available
to BeanKeeper, or you renamed it, perhaps moved it to another package.

> Thanks,
> Shay

Robert.