[odb-users] Schema evolution on existing database

[Monika Idzik]

Hi,
I'm trying to add new columns to existing table in a MySQL database.
I followed the instructions regarding schema evolution, generating the code:

odb::core::schema_version v(m_db->schema_version());
odb::core::schema_version
bv(odb::core::schema_catalog::base_version(*m_db));
odb::core::schema_version
cv(odb::core::schema_catalog::current_version(*m_db));

if (v == 0) {
  odb::core::transaction t(m_db->begin());
  odb::core::schema_catalog::create_schema(*m_db);
  t.commit();
  } else if (v < cv) {
    if (v < bv) {
      std::cout << "Error: migration from this version is no longer
supported." << std::endl;
    }
    for (v = odb::core::schema_catalog::next_version(*m_db, v); v <= cv; v
= odb::core::schema_catalog::next_version(*m_db, v))
    {
      odb::core::transaction t(m_db->begin());
      odb::core::schema_catalog::migrate_schema_pre(*m_db, v);
      // Data migration goes here.
      odb::core::schema_catalog::migrate_schema_post(*m_db, v);
      t.commit();
    }
  } else if (v > cv) {
    std::cout << "Error: old application trying to access new database." <<
std::endl;
  }
}

I also added
#pragma db model version(1,1)

It all works well: when I'm changing to version (1,2) and adding new
columns.
However, I already have data in my current database that was created
without model versions and schema evolution code: this means that when I'm
adding the above code, the existing data is being removed (I assume while
doing odb::core::schema_catalog::create_schema(*m_db);)

Is there a way to add new columns to the existing database (so changing
database schema) without losing existing data in the database?

Thanks,
Monika