Queries dhidi ya mutations dhidi ya subscriptions katika GraphQL?

Question

IT Interview Practice · Accepted Answer

Hizi ni aina tatu za **operation**, kila moja imeunganishwa na root type katika schema:

- **Query** — husoma data. Fields hukimbia **kwa sambamba (parallel)** na hazipaswi kuwa na madhara ya pembeni (kama HTTP GET).
- **Mutation** — huandika data (kuunda/kusasisha/kufuta). Top-level fields hukimbia **mfululizo (sequentially)**, hivyo mpangilio unahakikishwa.
- **Subscription** — mkondo unaodumu kwa muda mrefu: server husukuma data mpya kwa client kupitia transport kama WebSockets kila mara tukio linapotokea.

```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
  }
}
```

Mutations huchukua **arguments** (mara nyingi object ya `input`) na zinapaswa **kurudisha data iliyoathiriwa** ili client iweze kujiweka mpya bila ombi la pili. Kanuni ya mfululizo ni muhimu: mutations mbili katika document moja — `deposit` kisha `withdraw` — daima hukimbia kwa mpangilio huo, ambapo query fields mbili zinaweza kusuluhika kwa wakati mmoja.

## Kwa nini ni muhimu

Wahoji hukagua kama unajua kuwa **queries ni parallel na hazina madhara ya pembeni ilhali mutations ni sequential**, na kwamba subscription inahitaji transport yenye state (WebSocket/SSE). Kurudisha data iliyosasishwa kutoka kwa mutation ni undani wa vitendo unaowatofautisha watu waliowahi kutuma GraphQL na wale walioisoma tu.

Kwa nini ni muhimu

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