Two assumptions held on the test's table and on nothing else.
It dropped deleted_at while an index still referred to it. MySQL and
PostgreSQL drop dependent indexes along with the column; SQLite refuses,
and the migration stopped at the first table with such an index - which
is all thirteen of them.
It also read the rows through a column named id. sys_dept keys on
dept_id, sys_user on user_id, and only some tables on id, so the pass
that carries the deletion timestamps across never ran.
The test's table had an id key and no index on deleted_at, which is
exactly the shape that lets both through. It now matches sys_user.
sys_user.username, sys_role.role_key and sys_dict_type.dict_type had no
unique index. Uniqueness was a SELECT COUNT followed by an INSERT, which
two concurrent requests both pass — and login resolves a username with
First, so which of the two accounts answers is whichever the database
returns.
The index cannot be on the key alone, because a soft-deleted row keeps
occupying the name and a deleted user's username could never be used
again. It has to include the delete marker, and the marker has to be
non-null: two live rows are (alice, NULL) and (alice, NULL), and NULL is
not equal to NULL, so an index over a nullable marker admits both. That
is the worst of the three states — a constraint that reads as protection
and binds nothing — and there is a test that demonstrates it rather than
asserting it.
ModelTime.DeletedAt is milliseconds since the epoch now, zero while the
row is live. Sixteen tables carry it; the migration converts each one,
preserving when each deleted row was deleted, then adds the three
indexes.
Written to be re-runnable rather than transactional, because DDL does not
roll back on MySQL and an operator whose first attempt failed halfway
should have nothing to do but run it again. It refuses before altering
anything if a table already holds duplicates, naming them, rather than
letting the index fail and leaving the operator to guess.
The timestamp conversion happens in Go: turning a timestamp into epoch
milliseconds is spelled differently by every dialect this supports, and
these row counts do not justify four versions of it.
zhangwenjian