Kif tagħmel cache ta' API GraphQL?

Question

IT Interview Practice · Accepted Answer

Li tagħmel cache ta' GraphQL huwa aktar diffiċli minn REST għax hemm endpoint wieħed u r-requests normalment huma POST, allura l-caching HTTP ibbażat fuq URL ma jaħdimx out of the box. Minflok tagħmel cache fi tliet saffi: **klijent**, **transport/CDN**, u **server**.

## Cache normalizzata tal-klijent

Apollo Client u Relay jaħżnu r-riżultati f'**cache normalizzata** bil-key ta' `__typename` + `id`. Kull object jinħażen darba; queries differenti li jirreferu għall-istess `User:1` jaqsmuh, allura mutation li taġġorna entità waħda taġġorna kull view awtomatikament.

```graphql
# Both queries write to the same normalized entry User:1 in the client cache
query A { user(id: "1") { id name } }
query B { post(id: "9") { author { id name } } }  # author is also User:1
```

Huwa għalhekk li l-fields għandhom jirritornaw `id` — il-cache teħtieġ key stabbli biex tiddeduplika.

## Persisted queries + CDN

**Persisted queries** jissostitwixxu l-query string b'hash. Il-klijent jibgħat hash qasir minflok body POST twil; is-server ifittex il-query rreġistrata.

```js
// Automatic Persisted Queries: first a tiny GET with just the hash
// GET /graphql?extensions={"persistedQuery":{"sha256Hash":"abc..."}}
// -> because it's a GET with a stable key, a CDN can cache the RESPONSE at the edge
```

Li tibdel il-queries tal-qari f'GETs li jistgħu jiġu cached iħalli **CDN** iservihom fl-edge, u jnaqqas il-payloads. Il-hints `@cacheControl` (max-age, scope) iħallu s-server jiddikjara TTLs per-field li l-cache tal-CDN u tas-server Apollo jirrispettaw.

## Fuq in-naħa tas-server

Cache tar-response (eż. dik ta' Apollo) bil-key tal-query + variables + auth scope tevita li terġa' tħaddem ir-resolvers; DataLoader jimmaniġġja d-de-duplikazzjoni per-request (kwistjoni differenti — mhijiex cache cross-request).

## Għaliex huwa importanti

Id-disinn ta' endpoint wieħed/POST ikisser il-caching HTTP naïve, allura l-intervistaturi jridu jisimgħu t-tweġiba **b'saffi**: cache normalizzata tal-entitajiet fuq il-klijent, persisted queries + `@cacheControl` biex tinfetaħ il-caching tal-CDN/edge, u fejn jidħol DataLoader (per-request, mhux cross-request).

Cache normalizzata tal-klijent

Persisted queries + CDN

Fuq in-naħa tas-server

Għaliex huwa importanti

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