NestJS GraphQL Code-First

Object Types With Decorators

Mark model classes with @ObjectType() and fields with @Field(). Nest uses these metadata declarations (plus resolvers) to emit schema.gql.

@ObjectType()
export class Cat {
  @Field(() => ID)
  id: string;

  @Field()
  name: string;

  @Field({ nullable: true })
  breed?: string;
}

Nullable fields must be marked { nullable: true } or GraphQL will treat them as required.

Enabling Auto Schema File

GraphQLModule.forRoot({
  driver: ApolloDriver,
  autoSchemaFile: true, // or a path like 'src/schema.gql'
})

• Code-first keeps schema and TypeScript types aligned in one place.
• Generated schema files can be committed for review or gitignored—pick a team convention.
• Use @InputType() for mutation inputs and @ArgsType() for query argument groups.
• Unions, enums, and interfaces have matching Nest GraphQL decorators.

Code-First Cheatsheet

Decorators that drive schema generation.

Pros and Cons

Pros: single language, strong Nest/TS integration. Cons: schema design can feel secondary, and generated SDL may need review discipline for API contracts.

Sharing Types Across Modules

Keep GraphQL model classes in a shared or feature-owned models/ folder imported by resolvers. Avoid circular imports between resolvers and models.

Common Mistakes

• Forgetting nullable: true and generating incorrect required fields.
• Exposing every entity column as a GraphQL field by habit.
• Not reviewing generated SDL after larger type changes.
• Mixing code-first models with competing schema-first files without a clear boundary.

Key Takeaways

• Code-first uses TypeScript decorators to generate GraphQL schema.
• @ObjectType and @Field define the public GraphQL model.
• autoSchemaFile writes the SDL Nest generates.
• Treat generated schema as an API contract worth reviewing.