bug: check if exists for trophy migrations (#158)

Author: lukepolo

hasura/migrations/default/1776430500000_tournament_trophies_unique_include_placement/down.sql

@@ -1,5 +1,5 @@
 ALTER TABLE public.tournament_trophies
-    DROP CONSTRAINT tournament_trophies_tournament_team_player_placement_key;
+    DROP CONSTRAINT IF EXISTS tournament_trophies_tournament_team_player_placement_key;
 
 ALTER TABLE public.tournament_trophies
     ADD CONSTRAINT tournament_trophies_tournament_id_tournament_team_id_player_key

hasura/migrations/default/1776430500000_tournament_trophies_unique_include_placement/up.sql

@@ -1,8 +1,31 @@
 -- Allow a player to hold both a placement trophy (gold/silver/bronze) and MVP
 -- on the same tournament. The old uniqueness key blocked the second insert
 -- when the MVP was on the winning team.
-ALTER TABLE public.tournament_trophies
-    DROP CONSTRAINT tournament_trophies_tournament_id_tournament_team_id_player_key;
+--
+-- The previous constraint was created via an inline UNIQUE (...) in the
+-- original migration, so its name is auto-generated by Postgres. The exact
+-- truncation of that name varies across Postgres versions / NAMEDATALEN, so
+-- look it up by column set instead of relying on the expected name.
+DO $$
+DECLARE
+    v_conname text;
+BEGIN
+    SELECT c.conname
+    INTO v_conname
+    FROM pg_constraint c
+    WHERE c.conrelid = 'public.tournament_trophies'::regclass
+      AND c.contype = 'u'
+      AND (
+          SELECT array_agg(a.attname ORDER BY a.attname)
+          FROM unnest(c.conkey) AS k(attnum)
+          JOIN pg_attribute a
+            ON a.attrelid = c.conrelid AND a.attnum = k.attnum
+      ) = ARRAY['player_steam_id', 'tournament_id', 'tournament_team_id']::text[];
+
+    IF v_conname IS NOT NULL THEN
+        EXECUTE 'ALTER TABLE public.tournament_trophies DROP CONSTRAINT ' || quote_ident(v_conname);
+    END IF;
+END $$;
 
 ALTER TABLE public.tournament_trophies
     ADD CONSTRAINT tournament_trophies_tournament_team_player_placement_key