"Chanzo kimoja cha ukweli" kinamaanisha nini?

Question

Accepted Answer

**Chanzo kimoja cha ukweli** kinamaanisha kwamba kila sehemu ya data inakohifadhiwa **katika mahali moja tu**, na kila kitu kinachohitaji hiyo kinasoma hapo — badala ya kuandika nakala nyingi ambazo zinaweza kukamatiana.

## Tatizo linalokaa: hali iliyonakiliwa, inayokukamatiana

```jsx
// ❌ the same data stored in two places → they can disagree
function Profile() {
  const [user, setUser] = useState({ name: "Ann" });
  const [displayName, setDisplayName] = useState("Ann"); // a COPY of user.name

function rename(newName) {
    setUser({ ...user, name: newName }); // updated user...
    // ...but forgot to update displayName → now they're out of sync! 🐛
  }
}
```

Kawaida wakati ukweli sawa unaishi katika majimbe mawili, kila update lazima ikumbuke kubadilisha zote — na bila shaka moja husahau, na kutengeneza hitilafu ambapo UI inaonyesha thamani zisizofanana.

## Suluhu: chanzo kimoja, tokeza mengine

```jsx
// ✅ user.name is the single source; displayName is DERIVED, not stored
function Profile() {
  const [user, setUser] = useState({ name: "Ann" });
  const displayName = user.name.toUpperCase(); // computed on render — always in sync

function rename(newName) {
    setUser({ ...user, name: newName }); // one update, everything stays consistent
  }
}
```

Hifadhi thamani kanoni mara moja; hesabu kila kitu kinachoweza kutokana nayo ndani ya mapambano. Hakuna kitu cha kuandika katika synchronization.

## Mahali ambapo kanuni hii inatumika

```text
✓ Don't copy props into state (the prop is the source)
✓ Don't store derived values (compute them: totals, filtered lists, formatted text)
✓ Global stores (Redux/Pinia): one store is the source for shared data
✓ Server data: cache it once (React Query) rather than copying into many components
✓ URL as source: filters/page in the URL, read from there
```

## Kwa nini ni muhimu

Chanzo kimoja cha ukweli ni kanuni ya msingi ya usimamizi wa hali ya amanisha — inaondoa darasa lote la hitilafu zinazosababishwa na data iliyonakiliwa kukamatiana.

Ni *kwa nini* unatokeza thamani badala ya kuziandika, *kwa nini* unazuia kunakili props katika hali, na *kwa nini* duka la kimataifa linakuza data iliyoshirikiwa.

Wakati data ina nyumba moja ya mamlaka na kila kitu kinasoma kutoka hapo, UI yako inabaki sawa kwa muundo.