I want to establish the identical response output field name in NestJS by utilizing the @Expose decorator from class-transformer

Question

I want to establish the identical response output field name in NestJS by utilizing the @Expose decorator from class-transformer

My Entity definition currently looks like this:

export class ItemEntity implements Item {

  @PrimaryColumn()
  @IsIn(['product', 'productVariant', 'category'])
  @IsNotEmpty()
  itemType: string;

  @PrimaryColumn()
  @IsUUID()
  @IsNotEmpty()
  itemId: string;

  @OneToOne(() => ProductEntity, product => product.id, { nullable: true })
  @JoinColumn()
  @Expose({ name: 'bundleItem' })
  producttItem: ProductEntity;

  @OneToOne(() => ProductVariantEntity, variant => variant.id, {
    nullable: true,
  })
  @JoinColumn()
  @Expose({ name: 'bundleItem' })
  variantItem: ProductVariantEntity;

  @OneToOne(() => CategoryEntity, category => category.id, { nullable: true })
  @JoinColumn()
  @Expose({ name: 'bundleItem' })
  categoryItem: CategoryEntity;
}

My use of the @Expose() decorator is to ensure that only one of productItem, variantItem, or categoryItem is returned as a single bundleItem field in the response. Only one of them should have a value, not two or three.

However, upon performing a GET request on the ItemEntity's controller, the desired effect is applied only to the first item, not the rest:

[
    {
        "itemType": "category",
        "itemId": ""
        "bundleItem": {
            "categoryType": "Custom",
            "description": "First custom category",
            "id": "e00ad76c-95d3-4215-84b1-de17c7f1f82c",
            "name": "Category A",
            "updatedAt": "2023-02-24T08:49:22.913Z"
        }
    },
    {
        "itemType": "variant",
        "itemId": "",
        "bundletem": null
    }
]

I aim to extend this effect to all items in the response array. Currently, the other items are returning as null. In essence, I want the response to include a bundleItem field regardless of the itemType (be it productItem, variantItem, or categoryItem). Is it possible to achieve this using `class-transformer`?

Thank you.

javascript typescript nestjs typeorm class-transformer

Answer 1

Answer №1

If you're looking to streamline your transformation process, consider utilizing the @Transform decorator. This decorator offers various arguments that can be leveraged during the transform operation, including access to the object itself.

@Transform(({ value, key, obj, type }) => value)

For instance, in the code snippet below, we have an object with two properties. If one of these properties is either null or undefined, the other property is returned instead.

import {Exclude, Expose, Transform} from "class-transformer";

export class ExampleDto {
  constructor(partial: Partial<ExampleDto>) {
    Object.assign(this, partial);
  }

  @Expose()
  name: string;

  @Expose({ name: "new_property" })
  @Transform(({ value, key, obj, type }) => {
    return obj.property1 ?? obj.property2;
  })
  property1: string | null;

  @Exclude()
  property2: string | null;
}

Within the Controller:

  @Get("example")
  @UseInterceptors(ClassSerializerInterceptor)
  getExample(): ExampleDto {
    return new ExampleDto({
      name: "Name",
      property2: "value 2"
    });
  }

The output will be:

{
    "name": "Name",
    "new_property": "value 2"
}

While this approach may be effective, it is strongly advised to separate your database entity from the DTOs. Using the same class for both purposes can lead to potential issues, as the entity serves as a representation in the database and a contract with the external world simultaneously. Any modifications to your model will impact the API and vice versa.

Answer 2

If you're looking to streamline your transformation process, consider utilizing the @Transform decorator. This decorator offers various arguments that can be leveraged during the transform operation, including access to the object itself.

@Transform(({ value, key, obj, type }) => value)

For instance, in the code snippet below, we have an object with two properties. If one of these properties is either null or undefined, the other property is returned instead.

import {Exclude, Expose, Transform} from "class-transformer";

export class ExampleDto {
  constructor(partial: Partial<ExampleDto>) {
    Object.assign(this, partial);
  }

  @Expose()
  name: string;

  @Expose({ name: "new_property" })
  @Transform(({ value, key, obj, type }) => {
    return obj.property1 ?? obj.property2;
  })
  property1: string | null;

  @Exclude()
  property2: string | null;
}

Within the Controller:

  @Get("example")
  @UseInterceptors(ClassSerializerInterceptor)
  getExample(): ExampleDto {
    return new ExampleDto({
      name: "Name",
      property2: "value 2"
    });
  }

The output will be:

{
    "name": "Name",
    "new_property": "value 2"
}

While this approach may be effective, it is strongly advised to separate your database entity from the DTOs. Using the same class for both purposes can lead to potential issues, as the entity serves as a representation in the database and a contract with the external world simultaneously. Any modifications to your model will impact the API and vice versa.

I want to establish the identical response output field name in NestJS by utilizing the @Expose decorator from class-transformer

Answer №1

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