feat(migration): enhance primary key handling and add GIN index support in migration writer

pkg/writers/pgsql/templates/create_primary_key_with_autogen_check.tmpl

@@ -1,26 +1,42 @@
 DO $$
 DECLARE
-  auto_pk_name text;
+  current_pk_name text;
+  current_pk_matches boolean := false;
 BEGIN
-  -- Drop auto-generated primary key if it exists
-  SELECT constraint_name INTO auto_pk_name
-  FROM information_schema.table_constraints
-  WHERE table_schema = '{{.SchemaName}}'
-    AND table_name = '{{.TableName}}'
-    AND constraint_type = 'PRIMARY KEY'
-    AND constraint_name IN ({{.AutoGenNames}});
+  SELECT tc.constraint_name,
+         COALESCE(
+           ARRAY(
+             SELECT a.attname
+             FROM pg_constraint c
+             JOIN pg_class t ON t.oid = c.conrelid
+             JOIN pg_namespace n ON n.oid = t.relnamespace
+             JOIN unnest(c.conkey) WITH ORDINALITY AS cols(attnum, ord)
+               ON TRUE
+             JOIN pg_attribute a
+               ON a.attrelid = t.oid
+              AND a.attnum = cols.attnum
+             WHERE c.contype = 'p'
+               AND n.nspname = '{{.SchemaName}}'
+               AND t.relname = '{{.TableName}}'
+             ORDER BY cols.ord
+           ),
+           ARRAY[]::text[]
+         ) = ARRAY[{{.ColumnNames}}]
+    INTO current_pk_name, current_pk_matches
+  FROM information_schema.table_constraints tc
+  WHERE tc.table_schema = '{{.SchemaName}}'
+    AND tc.table_name = '{{.TableName}}'
+    AND tc.constraint_type = 'PRIMARY KEY';
 
-  IF auto_pk_name IS NOT NULL THEN
-    EXECUTE 'ALTER TABLE {{qual_table .SchemaName .TableName}} DROP CONSTRAINT ' || quote_ident(auto_pk_name);
+  IF current_pk_name IS NOT NULL
+     AND NOT current_pk_matches
+     AND current_pk_name IN ({{.AutoGenNames}}) THEN
+    EXECUTE 'ALTER TABLE {{qual_table .SchemaName .TableName}} DROP CONSTRAINT ' || quote_ident(current_pk_name);
   END IF;
 
-  -- Add named primary key if it doesn't exist
-  IF NOT EXISTS (
-    SELECT 1 FROM information_schema.table_constraints
-    WHERE table_schema = '{{.SchemaName}}'
-      AND table_name = '{{.TableName}}'
-      AND constraint_name = '{{.ConstraintName}}'
-  ) THEN
+  -- Add the desired primary key only when no matching primary key already exists.
+  IF current_pk_name IS NULL
+     OR (NOT current_pk_matches AND current_pk_name IN ({{.AutoGenNames}})) THEN
     ALTER TABLE {{qual_table .SchemaName .TableName}} ADD CONSTRAINT {{quote_ident .ConstraintName}} PRIMARY KEY ({{.Columns}});
   END IF;
 END;