使用 type-graphql 和 RESTDataSource 为第二个 api 调用添加字段解析器

Question

我们希望下面的查询根据返回的truckId 解析truck 字段：

实体

// RosterEntity.ts
import { Truck } from '@sap-truck-roster/entity/Truck'
import { Field, ID, ObjectType } from 'type-graphql'

@ObjectType()
export class Roster {
  @Field(() => Truck, { nullable: true })
  truck: Truck
  
  @Field(() => ID)
  readonly truckId: string
}

// TruckEntity.ts
import { Field, ID, ObjectType } from 'type-graphql'

@ObjectType()
export class Truck {
  @Field(() => ID)
  readonly id: string

  @Field()
  readonly description: string
}

解析器

// TruckResolver.ts
import { Resolver, Arg, Query, Ctx, Field, ObjectType, createUnionType,} from 'type-graphql'
import { Truck } from '@sap-truck-roster/entity/Truck'
import { plainToClass } from 'class-transformer'
import { Context } from '@shared/typings'
import { ApiError } from '@shared/graphql'

@ObjectType()
class TruckArray {
  @Field(() => [Truck], { nullable: true })
  data?: [Truck]
}

const TruckQueryResultUnion = createUnionType({
  name: 'TruckQueryResult',
  // types: () => [[Truck], ApiError] as const,
  // an array is not supported by the Graphql spec in unions
  types: () => [TruckArray, ApiError] as const,
})

@Resolver(() => Truck)
export class TruckResolver {
  @Query(() => TruckQueryResultUnion)
  async truck(
    @Ctx() ctx: Context,
    @Arg('id', { nullable: true }) id?: string,
    @Arg('country', { nullable: true }) country?: string
  ): Promise<typeof TruckQueryResultUnion> {
      const response = await ctx.dataSources.sapTruckRosterAPI.getTruck({ id, country })

      return plainToClass(TruckArray, { data: response.data, })
  }
}

// RosterResolver.ts
import { Resolver, Arg, Query, Ctx, Field, ObjectType, createUnionType,} from 'type-graphql'
import { Roster } from '@sap-truck-roster/entity/Roster'
import { plainToClass } from 'class-transformer'
import { Context } from '@shared/typings'
import { ApiError } from '@shared/graphql'
import { Truck } from '@sap-truck-roster/entity/Truck'

@ObjectType()
class RosterArray {
  @Field(() => [Roster], { nullable: true })
  data?: [Roster]
}

const RosterQueryResultUnion = createUnionType({
  name: 'RosterQueryResult',
  // types: () => [[Roster], ApiError] as const,
  // an array is not supported by the Graphql spec in unions
  types: () => [RosterArray, ApiError] as const,
})

@Resolver(() => Roster)
export class RosterResolver {
  @Query(() => RosterQueryResultUnion)
  async roster(
    @Ctx() ctx: Context,
    @Arg('date', () => String) date: string,
    @Arg('truckId', { nullable: true }) truckId?: string,
    @Arg('driverId', { nullable: true }) driverId?: string
  ): Promise<typeof RosterQueryResultUnion> {
      const response = await ctx.dataSources.sapTruckRosterAPI.getRoster({ date, driverId, truckId })

      // @FieldResolver(() => Truck)
      // truck(@Root() truck: Truck) {
      //   return await ctx.dataSources.sapTruckRosterAPI.getTruck({
      //     id: response.truckId
      //   })
      // }
      
     return plainToClass(RosterArray, { data: response.data })
  }
}

正如您在RosterResolver.ts 中看到的，我们尝试使用response.truckId 来查询API 上的另一个端点，但失败了。用数据填充 truck 字段的正确方法是什么？

这会在控制台中返回正确的数据，但与 roster 不匹配，因为我们获得了所有 truck 属性的 null 值：

  // RosterResolver.ts

  @FieldResolver(() => Truck, { nullable: true })
  async truck(@Root() roster: Roster, @Ctx() ctx: Context) {
    console.log('roster.truckId: ', roster.truckId)

    const response = await ctx.dataSources.sapTruckRosterAPI.getTruck({
      id: roster.truckId,
    })

    console.log('response: ', response);
    
    return response
  }

Answer 1

您可以做的是解析器继承。 https://github.com/MichalLytek/type-graphql/blob/master/docs/resolvers.md#field-resolvers

@Resolver(() => Roster)
export class RosterResolver {

  ....

  @FieldResolver()
  truck(@Root() roster: Roster) {
    return ctx.dataSources.sapTruckRosterAPI.getTruck({
      id: roster.truckId
    });
  }