Class-validator - validate array of objects

You can use the following:

validator.arrayNotEmpty(array); // Checks if given array is not empty.

validator.arrayMinSize(array, min); // Checks if array's length is at least `min` number.

(https://github.com/typestack/class-validator#manual-validation)

You may want to consider writing custom validator which would better reflect the business requirement you have.

const param1: AuthParam = Object.assign(new AuthParam(), {
  id: 1,
  type: 'grant',
  value: 'password'
})

const param2: AuthParam = Object.assign(new AuthParam(), {
  id: 1,
  type: 4,
  value: 'password'
})

const signInTest = new SignInModel()
signInTest.authParameters = [param1, param2]

validate(signInTest).then(e => {
  console.log(e[0].children[0].children[0])
})

This works correctly, this is:

ValidationError {
  target: AuthParam { id: 1, type: 4, value: 'password' },
  value: 4,
  property: 'type',
  children: [],
  constraints: { isString: 'type must be a string' } }

so I may only assume that object which is being validated, is not an instance of AuthParam

const param2: AuthParam = {
  id: 1,
  type: 4,
  value: 'password'
} as any

as expected, there aren't any decorators on this object (which may be true for Nest.js controllers and nested objects from body/req) - so validation is ignored.

Please check this (tl;dr - @Type decorator form class-transformer)

I Know I Am Late But Facing Some Issue With Type, Then Try Another Way To Implement This:

export class AuthParam {
    @IsNumber()
    id: number;
  
    @IsString()
    type: string;
  
    @IsString()
    value: string;
  }

Validation function

@ValidatorConstraint()
export class IsAuthArray implements ValidatorConstraintInterface {
    public async validate(authData: AuthParam[], args: ValidationArguments) {
        return Array.isArray(authData) && authData.reduce((a, b) => a && (typeof b.id === "number") && typeof b.type === "string" && typeof b.field === "string", true);
    }
}

export class SignInModel {
    @IsNotEmpty()
    @IsArray()
    @ArrayMinSize(2)
    @ArrayMaxSize(2)
    @Validate(IsAuthArray, {
        message: "Enter valid value .",
    })
    authParameters: AuthParam[];
  }

Maybe It Will Help Someone 😃

Add @Type(() => AuthParam) to your array and it should be working. Type decorator is required for nested objects(arrays). Your code becomes

import { IsArray, ValidateNested, ArrayMinSize, ArrayMaxSize } from 'class-validator';
import { AuthParam } from './authParam.model';
import { Type } from 'class-transformer';

export class SignInModel {
  @IsArray()
  @ValidateNested({ each: true })
  @ArrayMinSize(2)
  @ArrayMaxSize(2)
  @Type(() => AuthParam)
  authParameters: AuthParam[];
}

Be careful if you are using any exception filter to modify the error reponse. Make sure you understand the structure of the class-validator errors.