Schema ya GraphQL ni nini? Eleza scalar na object types.

Question

IT Interview Practice · Accepted Answer

**Schema** ni mkataba wenye types wa API ya GraphQL ulioandikwa kwa SDL (Schema Definition Language). Huelezea kila type, kila field, na **root types** maalum — `Query` (kusoma), `Mutation` (kuandika), na kwa hiari `Subscription` (moja kwa moja/live). Server hukataa ombi lolote lisilolingana na schema.

## Scalar dhidi ya object types

- **Scalar types** ni thamani za majani (leaf) zinazoshikilia data halisi: zilizojengwa ndani ni `Int`, `Float`, `String`, `Boolean`, na `ID`. Unaweza pia kufafanua scalars maalum kama `DateTime`.
- **Object types** hukusanya fields pamoja. Fields zake zinaweza kuwa scalars *au* object types nyingine, ambavyo ndivyo unavyomodeli mahusiano.

```graphql
scalar DateTime                # a custom scalar

type User {                    # an object type
  id: ID!                      # ! means non-null (always present)
  name: String!
  createdAt: DateTime!
  posts: [Post!]!              # a list of Post objects, non-null list of non-null items
}

type Post {
  id: ID!
  title: String!
  author: User!                # points back to User -> a relationship
}

type Query {                   # root type: the entry points for reads
  user(id: ID!): User          # a field with an argument; returns a User (nullable)
}
```

`!` huonyesha **non-null**; `[Post!]!` ni list ya non-null ambayo vitu vyake ni non-null. Arguments (`id: ID!`) huruhusu field kuwekewa vigezo (parameterized).

## Kwa nini ni muhimu

Schema ndiyo chanzo kimoja cha ukweli — huendesha validation, docs zinazozalishwa kiotomatiki, na client codegen. Kusoma `!` na list types kwa usahihi ni ukaguzi wa kawaida wa uchujaji kwa junior, na maamuzi ya nullability huunda jinsi clients zinavyoshughulikia makosa.

Scalar dhidi ya object types

Kwa nini ni muhimu

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