Ok, I finally solved the problem.
I had to place the MySQL driver into app server classpath.
The thing is that, when trying to deploy my app, I was first receiving this error message:
Internal Exception: java.sql.SQLException: Error in allocating a connection. Cause: Class name is wrong or classpath is not set for : com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSourceError Code: 0
, but then I would try to deploy again and then the driver exception would not appear, but only the persistence unit problem, so I thought the driver problem was gone.
Please excuse my lack of experience.
Thank you all very much for your help !
Ivan
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