The defer closure checked a local err variable for commit/rollback
decisions, but err remained nil after a successful BeginTx. When
txBody failed, the error was returned directly without assigning to
err, so the defer always committed instead of rolling back.
Additionally, since err was not a named return value, the defer's
Commit error assignment was silently swallowed.
Replace the error-prone defer pattern with explicit rollback on
txBody failure and a direct Commit return.
Copy over all the code that the graph SQL migration needs to a
separate folder. This will let us advance the main graph SQL CRUD code
without worrying about changing the sql migration code. It will also let
us change the SQL queries without changing the migration. In this
commit, only the migration logic is "frozen" but in an upcoming commit,
the sqlc queries & models will be frozen too.
ziggie