Queries kontra mutations kontra subscriptions f'GraphQL?

Question

IT Interview Practice · Accepted Answer

Dawn huma t-tliet **operation types**, kull wieħed immappjat għal root type fis-schema:

- **Query** — taqra d-data. Il-fields jaħdmu **b'mod parallel** u ma jridux ikollhom side effects (bħal HTTP GET).
- **Mutation** — tikteb id-data (create/update/delete). Il-fields top-level jaħdmu **b'mod sekwenzjali**, allura l-ordni hija ggarantita.
- **Subscription** — stream ta' ħajja twila: is-server jimbotta data ġdida lill-klijent fuq transport bħal WebSockets kull meta jixgħel event.

```graphql
query GetPost {              # read
  post(id: "1") { title }
}

mutation AddComment {        # write; returns the created object so the client updates its cache
  addComment(postId: "1", text: "Nice!") {
    id
    text
  }
}

subscription OnComment {     # live: fires every time a comment is added
  commentAdded(postId: "1") {
    id
    text
  }
}
```

Il-mutations jieħdu **arguments** (spiss object `input`) u għandhom **jirritornaw id-data affettwata** biex il-klijent ikun jista' jaġġorna mingħajr it-tieni request. Ir-regola sekwenzjali hija importanti: żewġ mutations f'dokument wieħed — `deposit` imbagħad `withdraw` — dejjem jaħdmu f'dik l-ordni, filwaqt li żewġ query fields jistgħu jiġu solvuti fl-istess ħin.

## Għaliex huwa importanti

L-intervistaturi jivverifikaw li taf li **il-queries huma parallel u mingħajr side-effects filwaqt li l-mutations huma sekwenzjali**, u li subscription teħtieġ transport stateful (WebSocket/SSE). Li tirritorna data aġġornata minn mutation huwa d-dettall prattiku li jiddistingwi lil dawk li tabilħaqq użaw GraphQL fil-produzzjoni minn dawk li biss qraw dwaru.

Għaliex huwa importanti

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