sqlite3 doesn't support adding a foreign key via gorm.DB#AddForeignKey
this would mean, that we have some hacky solutions for having foreign
keys for sqlite and the other databases. Therefore manually deleting
the referencing models seems to be the best solution. We already have
interfaces for database capsuling, so no api must be adjusted.
we use the database connection inside the handlers from the http
framework, therefore concurrent access occurs. Sqlite cannot handle
concurrent writes, so we limit sqlite to one connection.
see https://github.com/mattn/go-sqlite3/issues/274
Jannis Mattheis