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Donkie
d43552bd26
A tag maps a UID to "the thing to bring up", and only some of those things are
spools -- or rows at all. Locations are the case that settles the shape: a
location in Spoolman is a String(64) on Spool, not a table, so a tag meaning
"show me Shelf A" can never be a foreign key.
Getting this wrong is asymmetrically expensive. Renaming the table, dropping
spool_id's NOT NULL and adding a discriminator all mean altering a populated
table on four databases; adding an endpoint or a target kind later is additive
and free. The migration has shipped to nobody -- it is not on master and
v0.26.1 predates it -- so the schema is settled now and the unshipped revision
is rewritten in place rather than chased with a second one.
spool_tag becomes tag:
uid unchanged, still globally unique -- one physical tag, one thing
target_type which kind of target is in force, rather than leaving readers
to infer it from whichever column is non-null
spool_id nullable now; targets that ARE rows keep real foreign keys, so
filament_id the database still cascades deletes and refuses orphans
target_value targets that are not rows; a new kind of this sort costs no
migration at all, only a new target_type string
Exactly-one-target is enforced in database/tag.py rather than by a CHECK: no
migration in this tree uses one, and MySQL below 8.0.16 parses and silently
ignores them, so a constraint here would be real on three databases out of
four. Single write path beats a constraint that is only sometimes a constraint
-- the same argument, in the same module, as normalize_uid.
filament_id gets a column and a foreign key but no ORM relationship: nothing
writes filament tags, and a selectin collection on Filament would add a query
to every filament listing for rows that cannot exist. ON DELETE CASCADE holds
integrity until the feature that needs the relationship arrives.
No API surface changes. POST /spool/{id}/tag, ?tag=, the spool response's tags
and matched_spool_id are all exactly as they were; the reads are just explicit
now about wanting a spool rather than assuming the tag they found is one.
TagConflictError's spool_id becomes optional for the same reason, which the
client already handled -- it only offers "move it here" when there is an id.
Proven on sqlite, postgres, mariadb and cockroachdb: 526 integration tests each.