CODEWITHSUNDEEP
graphqlannotationsnestjs
masood keshvari
masood keshvari

Reputation: 51

how use Generics declaration in ObjectType field annotation (nestjs)

I need create custom pagination result for my graphql types.

this is my PaginateResults @ObjectType :

@ObjectType()
export class PaginateResult<T> {
    @Field()
    docs: T[];
    
    @Field()
    totalDocs: string;
    
    @Field()
    totalPages: string;
}

and its invocation in the resolvers:

@Query((type) => PaginateResult<User>, { nullable: true })
async getUsers(@Args({ type: () => GetAllUserArgs }) args: GetAllUserArgs) {
    const queryResolver: QueryResolver = new QueryResolver(args);
    return this.userService.getAll(queryResolver.query);
}

and Users @ObjectType

@ObjectType()
export class User {
    @Field(() => ID)
    id: string;
    
    @Field()
    fullName: string;
    
    @Field()
    companyName: string;
    
    @Field()
    mobile: string;
    
    @Field({ nullable: true })
    profilePhoto?: string;
    
    @Field()
    isActive: boolean;
}

But, this does not work and I get this error:

Error: Undefined type error. Make sure you are providing an explicit type for the "docs" of the "PaginateResult" class.

Upvotes: 5

Views: 2556

Answers (1)

Gustavo
Gustavo

Reputation: 141

You have to define a PaginateResult type:

import { Field, Int, ObjectType } from '@nestjs/graphql';
import { Type } from '@nestjs/common';

export function PaginateResult<T>(ItemType: Type<T>): any {
  @ObjectType({ isAbstract: true })
  abstract class PageClass {
    @Field(() => [ItemType])
    docs: T[];

    @Field(() => Int)
    totalPages: number;
  }

  return PageClass;
}

use the generic function factory to create a dedicated type class:

import { User } from './user.model';
import { ObjectType } from '@nestjs/graphql';
import { Paginated } from 'src/types/paginated-result.type';

@ObjectType()
export class UserPage extends PaginateResult(User) {}

and call it in resolver

  @Query(() => UserPage)
  async getUsers(
    @Args() args: GetAllUserArgs,
  ): Promise<UserPage | HttpException> {
    return this.usersService.getAll(args);
  }

Upvotes: 11

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