Validate an array of objects with class-validator and Nest.js

Question

I am using class-validator with NestJS and trying to validate an array of objects, with this layout:

[
    {gameId: 1, numbers: [1, 2, 3, 5, 6]},
    {gameId: 2, numbers: [5, 6, 3, 5, 8]}
]

My resolver

createBet(@Args('createBetInput') createBetInput: CreateBetInput) {
    return this.betsService.create(createBetInput);
  }

My createBetInput DTO

import { InputType, Field, Int } from '@nestjs/graphql';
import { IsArray, IsNumber } from 'class-validator';

@InputType()
export class CreateBetInput {
  @IsNumber()
  @Field(() => Int)
  gameId: number;

  @Field(() => [Int])
  @IsArray()
  numbers: number[];
}

I've tried some solutions but I haven't been successful, honestly, I have no idea how to do this.

How can I modify the DTO to get the necessary validation?

Dont forget ` @Type(()=>LineDto)` on the arrary field

Gilbert
– Gilbert

2023-10-12 12:51:10 +00:00
Commented Oct 12, 2023 at 12:51 — Gilbert
– Gilbert, Commented Oct 12, 2023 at 12:51

Heartbit · Accepted Answer · 2021-12-15 22:52:46Z

7

There are options of class-validator mixed with class-transformer to validating nested objects, your Array also is a nested object, so you can validate that like this:

import { Type } from 'class-transformer';
import { IsArray, ValidateNested } from 'class-validator';

class ItemsOfBet {
  @IsArray()
  @ValidateNested({ each: true })
  @Type(() => CreateBetInput)
  items: CreateBetInput[];
}

answered Dec 15, 2021 at 22:52

Heartbit

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3 Comments

Gilbert Over a year ago

It should be emphasized that the @Type line is important else the validation wont take place

Deekshith Anand Over a year ago

cant this be done without creating a new type for hosting array, what if i just wanted to use CreateBetInput[] at controller level?

Heartbit Over a year ago

@DeekshithAnand as we get body data from the controller's parameters and they usually are in JSON objects with the format of {...data} and best practices say not to use array formats for the top level of the body objects like [...data] so this is a right pattern.

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