What is the difference between @ObjectType() and @InputType() in NestJS GraphQL and why can't you reuse the same class for both?

Q: What is the difference between @ObjectType() and @InputType() in NestJS GraphQL and why can't you reuse the same class for both?

// Wrong — cannot use @ObjectType as mutation input @ObjectType() export class User { @Field(() => Int) id: number; @Field() email: string; } // createUser(@Args('user') user: User) — throws at runtime // Correct — separate classes for input and output @InputType() export class CreateUserInput { @Field() email: string; @Field() password: string; } @ObjectType() export class User { @Field(() => Int) id: number; @Field() email: string; } // OmitType bridge — derive InputType from ObjectType // Third argument tells NestJS to use @InputType() decorators @InputType() export class CreateUserInput extends OmitType(User, ['id'] as const, InputType) { @Field() password: string; // add fields not on the ObjectType } @ObjectType() — output only; can contain resolver methods, computed properties, and lazy-loaded relations. @InputType() — input only; all fields must be serializable scalars or nested @InputType() classes. GraphQL schema has separate type registries for Input and Object types — they cannot be mixed. OmitType(User, ['id'], InputType) re-registers fields from an @ObjectType() as an @InputType(). PickType, PartialType, and OmitType from @nestjs/mapped-types bridge output and input types safely.

Difficulty: 5/10

GraphQL schema, NestJS decorators, type safety

@ObjectType() defines a GraphQL output type that can contain resolvers, computed fields, and relations. @InputType() defines a GraphQL input type where all fields must be serializable scalars or nested input types. They are distinct schema types and NestJS will throw a runtime error if you try to use an @ObjectType() as a mutation argument.

ObjectType vs InputType and MappedTypes bridge

Key differences:

1
@ObjectType() — output only; can contain resolver methods, computed properties, and lazy-loaded relations.
2
@InputType() — input only; all fields must be serializable scalars or nested @InputType() classes.

What is the difference between @ObjectType() and @InputType() in NestJS GraphQL and why can't you reuse the same class for both?

Difficulty: 5/10

GraphQL schema, NestJS decorators, type safety

@ObjectType() defines a GraphQL output type that can contain resolvers, computed fields, and relations. @InputType() defines a GraphQL input type where all fields must be serializable scalars or nested input types. They are distinct schema types and NestJS will throw a runtime error if you try to use an @ObjectType() as a mutation argument.

ObjectType vs InputType and MappedTypes bridge

Key differences:

1
@ObjectType() — output only; can contain resolver methods, computed properties, and lazy-loaded relations.
2
@InputType() — input only; all fields must be serializable scalars or nested @InputType() classes.

What is the difference between @ObjectType() and @InputType() in NestJS GraphQL and why can't you reuse the same class for both?

What is the difference between @ObjectType() and @InputType() in NestJS GraphQL and why can't you reuse the same class for both?

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