How to validate a List of nested Objects in nest.js

Question

I want to validate a list of nested Object @ the request:

export class Room {
  @ApiProperty()
  @IsNotEmpty()
  @IsString()
  name: string;

  @ApiProperty({ type: [RoomMate] })
  @IsNotEmpty()
  @IsArray()
  @ValidateNested({ each: true })
  roomMates: RoomMate[];
}

The documation linked at nest.js (https://github.com/typestack/class-validator#validating-arrays) only talks about nested Objects, but not about a List of nested objects

If I execute the code above it says:

{
  "statusCode": 400,
  "message": [
    "0.an unknown value was passed to the validate function"
  ],
  "error": "Bad Request"
}

If I delete "@ValidateNested({ each: true })" it won't be validated (you could pass eg Cats & Dogs instead of RoomMates)

Any idea?

mouche · Accepted Answer · 2021-06-30 13:35:04Z

2

For @ValidateNested, I've found you need to specify an @Type as well:

  @ApiProperty({ type: [RoomMate] })
  @IsNotEmpty()
  @IsArray()
  @ValidateNested({ each: true })
  @Type(() => RoomMate)
  roomMates: RoomMate[];

The class-validator README examples assume you're working with classes, and there's a section on validating plain objects. This example in the class-transformer README shows using @Type() to specify the type of a nested object.

Also, makes sure RoomMate is a class and not just a TypeScript interface.

See this issue on class-validator for some more information.

answered Jun 30, 2021 at 13:35

mouche

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1 Comment

koallalays Over a year ago

Thank you VEEEERRRY much .... yes now it works. There are totaly 3 modules which contains a decorator "Type" I've choosen this: import { Type } from 'class-transformer'; ... and now it works!

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