probo / rules

---
description: Upsert must RETURNING full row into pointer receiver, not use xmax
globs: "pkg/coredata/**/*.go"
alwaysApply: false
---

# Upsert: RETURNING full row into receiver

Upsert methods use a **pointer receiver** and `RETURNING` all struct columns to sync the receiver with the actual DB state. Save the original ID before the query; compare it with the returned ID to detect insert vs update.

Do **not** use `RETURNING (xmax = 0) AS inserted` — `xmax` is a PostgreSQL internal system column and is fragile.

```go
// GOOD — RETURNING full row, sync receiver
func (t *Thing) Upsert(ctx context.Context, conn pg.Tx) (inserted bool, err error) {
	q := `
INSERT INTO things (id, name, created_at, updated_at)
VALUES (@id, @name, @created_at, @updated_at)
ON CONFLICT (name) DO UPDATE
SET
	name       = EXCLUDED.name,
	updated_at = EXCLUDED.updated_at
RETURNING
	id,
	name,
	created_at,
	updated_at
`
	originalID := t.ID
	// ...args...

	rows, err := conn.Query(ctx, q, args)
	if err != nil {
		return false, fmt.Errorf("cannot upsert thing: %w", err)
	}
	defer rows.Close()

	row, err := pgx.CollectExactlyOneRow(rows, pgx.RowToStructByName[Thing])
	if err != nil {
		return false, fmt.Errorf("cannot collect upsert result: %w", err)
	}

	*t = row
	return originalID == t.ID, nil
}

// BAD — xmax trick
RETURNING (xmax = 0) AS inserted

// BAD — RETURNING only id without syncing receiver
RETURNING id
```

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