Main branch is not compatible with older .db files

The latest additions for the support of GeoIdentifierTag and GeoSerialIdentifier nodes made the main branch crash when opening older .db files, which do not contain tables for those nodes.

added GeoModelIO label

assigned to @rbianchi

mentioned in merge request !86 (merged)

mentioned in commit b53e7495

closed with merge request !86 (merged)

closed with commit 9887e70d