probo / rules

---
description: Enforce Relay fragments instead of passing fetched data as props
globs: "**/*.tsx"
alwaysApply: false
---

# Never pass fetched data as props — use Relay fragments

When a child component needs data from a GraphQL node, it MUST define its own
colocated fragment and receive a **fragment key** (`SomeFragment$key`), never
a plain object or individual fields extracted from the parent's query/fragment.

This applies even when the child only uses the data to seed local state (e.g.
an edit form that copies fields into `useState`).

```tsx
// BAD — parent extracts fields and passes a plain object
<EditCookieRow
  cookie={{ name: cookie.name, duration: cookie.duration }}
  onSave={handleSave}
/>

// GOOD — child owns its fragment, parent spreads it and passes the key
// In EditCookieRow.tsx:
export const editCookieRowFragment = graphql`
  fragment EditCookieRowFragment on Cookie { name duration description }
`;
interface EditCookieRowProps {
  cookieKey: EditCookieRowFragment$key;
  onSave: (cookie: CookieEntry) => void;
}

// In parent fragment:
// ...EditCookieRowFragment   (spread on the Cookie node)

// In parent JSX:
<EditCookieRow cookieKey={cookie} onSave={handleSave} />
```

Callback props (`onSave`, `onCancel`) and configuration props (`isUpdating`,
`variant`) are fine — only **domain data** must come from fragments.

For connection items (table rows, list entries rendered in `.map()`), see the
companion rule `relay-connection-item-components.mdc`.

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