NestJS: How to transform an array in a @Query object

nestjs class-validator class-transformer
yuva.le picture yuva.le · Dec 11, 2019 · Viewed 8.7k times · Source

I'm new to NestJS and I am trying to fill a filter DTO from query Parameters.

Here is what I have:

Query:

localhost:3000/api/checklists?stations=114630,114666,114667,114668

Controller

@Get()
public async getChecklists(@Query(ValidationPipe) filter: ChecklistFilter): Promise<ChecklistDto[]> {
    // ...
}

DTO

export class ChecklistFilter {

    @IsOptional()
    @IsArray()
    @IsString({ each: true })
    @Type(() => String)
    @Transform((value: string) => value.split(','))
    stations?: string[];

    // ...
}

With this, the class validator does not complain, however, in the filter object stations is not actually an array but still a single string.

I want to transform it into an array within the validation pipe. How can I achieve that?

Answer

Jay McDoniel picture Jay McDoniel · Dec 11, 2019

You can pass an instance of the ValidationPipe instead of the class, and in doing so you can pass in options such as transform: true which will make class-validatorand class-transformer run, which should pass back the transformed value.

@Get()
public async getChecklists(@Query(new ValidationPipe({ transform: true })) filter: ChecklistFilter): Promise<ChecklistDto[]> {
    // ...
}

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