X'inhu l-meaning ta' "single source of truth"?

Question

Accepted Answer

**Single source of truth** jfisser li kull piece ta' data titkejjel **eżattament f'post wieħed**, u kollox li jkollu bżonn miha jaqra minn hemm — minflok iżommu kopji multipli li jistgħu joffqu minn xulxin.

## Il-problema li tirripetiha: stat duplikat u divergent

```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! 🐛
  }
}
```

Meta l-istess fatt ikun f'żewġ states, kull update jeħtieġ jiftakar li jbiddel it-tnejn — u inevitabbilment waħda titwiewa, li tipproduċi bugs fejn l-UI turi valuri inkonsistenti.

## Il-fix: sors wieħed, iderriva l-baقi

```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
  }
}
```

Ikkejjel il-valur kanonika darba; ikkomputa kulma derivabbli minhu fuq il-fly. M'hemm xejn li jeħtieġ jibqa' sinkronizzat.

## Fejn japplikaw dan il-prinċipju

```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
```

## Għaliex jimpurtaha

Single source of truth hija prinċipju fundamentali tal-management ta' state affidabbli — telimina klassi sħiħa ta' bugs ikkawżati minn data duplikata li toffqu minn xulxin.

Hija *għaliex* iderriva valuri minflok iħżnu, *għaliex* tevita naqalba props f'state, u *għaliex* global stores iċentralizzaw data magħquda.

Meta d-data ikollha dar wieħed awtoritattiv u kollox jaqra minhu, l-UI tibqa' konsistenti skond il-kostruzzjoni.