Yaya GraphQL federation ke aiki don microservices?

Question

IT Interview Practice · Accepted Answer

**Federation** yana barin ayyuka da yawa da aka tura kansu kai su mallaki ɓangare na graph guda, wanda wani **gateway** ke haɗawa cikin schema guda da abokan ciniki suke tambaya. Shi ne maye gurbi na zamani na **schema stitching**, inda gateway yake haɗa schemas na nesa da hannu — federation yana matsar ƙa'idodin haɗawa cikin subgraphs kansu.

## Tsarin gine-gine

```text
                 ┌────────────────────────┐
   Client ─────▶ │  Gateway / Router      │  (composed supergraph)
                 └───────┬────────┬───────┘
                         │        │  plans + fans out sub-queries
              ┌──────────▼──┐  ┌──▼──────────┐  ┌──────────────┐
              │ Users svc    │  │ Reviews svc │  │ Products svc │
              │  type User   │  │  extends    │  │  type Product│
              │  @key(id)    │  │  User/Prod  │  │  @key(id)    │
              └──────────────┘  └─────────────┘  └──────────────┘
```

Kowane sabis wani **subgraph** ne. Sabis guda ne yake mallakar nau'i kuma wasu suna **extend** ɗinsa. Directive ɗin `@key` yana ba da suna ga filin/filayen da suke gano wata daftari a tsakanin ayyuka.

```graphql
# Users subgraph OWNS User
type User @key(fields: "id") {
  id: ID!
  name: String!
}

# Reviews subgraph EXTENDS User with fields it owns
type User @key(fields: "id") {
  id: ID! @external          # declared elsewhere; referenced here by key
  reviews: [Review!]!        # this subgraph contributes this field
}
```

Lokacin da tambaya ta bazu a tsakanin ayyuka, gateway yana **shirya** ta: ɗauko `User` daga Users, sannan ya kira **entity resolver** na subgraph ɗin Reviews (`__resolveReference`) da `{ id }` don cika `reviews`.

```js
// Reviews subgraph resolves the User reference the gateway hands it
const resolvers = {
  User: {
    __resolveReference: (ref, ctx) => ctx.reviewLoader.load(ref.id),
  },
};
```

## Federation da stitching

Stitching yana tara dabarar haɗawa a cikin gateway (mai rauni, dole gateway ta san kowa). Federation yana **rarraba** mallaka: ƙungiyoyi suna juya subgraph ɗinsu kansu, kuma ana tabbatar da haɗawa a cikin CI. Cinikin shi ne gateway/router mafi rikitarwa da shirya tambaya ta tsakanin ayyuka.

## Me ya sa yake da muhimmanci

A sikeli, ƙungiya guda ba za ta iya mallakar schema mai kama da monolith ba. Masu tambayoyin hira suna son ganin cewa ka fahimci **mallakar daftari ta `@key`, reference resolvers, da shirya tambaya** — da dalilin da ya sa federation ya fi stitching don sikelin ƙungiya, ba kawai kyawun fasaha ba.

Tsarin gine-gine

Federation da stitching

Me ya sa yake da muhimmanci

Tambayoyi masu alaƙa