@ValidateIf and Inside It Handle the Logic

Instead of layering multiple @ValidateIfs and validators, consolidate validation using a single custom @ValidateIf() for each conditional branch.

@ValidateIf((o) => o.transactionType === TransactionType.PAYMENT)

@IsNotEmpty({ message: 'Received amount is required for PAYMENT transactions' })

@IsNumber()

receivedAmount?: number;

@ValidateIf((o) => o.transactionType === TransactionType.SALE && o.receivedAmount !== undefined)

@IsEmpty({ message: 'Received amount should not be provided for SALE transactions' })

receivedAmount?: number;

Create a custom validator for receivedAmount:

import {
  registerDecorator,
  ValidationOptions,
  ValidationArguments,
} from 'class-validator';

export function IsValidReceivedAmount(validationOptions?: ValidationOptions) {
  return function (object: any, propertyName: string) {
    registerDecorator({
      name: 'isValidReceivedAmount',
      target: object.constructor,
      propertyName: propertyName,
      options: validationOptions,
      validator: {
        validate(value: any, args: ValidationArguments) {
          const obj = args.object as any;
          if (obj.transactionType === 'PAYMENT') {
            return typeof value === 'number' && value !== null;
          } else if (obj.transactionType === 'SALE') {
            return value === undefined || value === null;
          }
          return true;
        },
        defaultMessage(args: ValidationArguments) {
          const obj = args.object as any;
          if (obj.transactionType === 'SALE') {
            return 'receivedAmount should not be provided for SALE transactions';
          }
          if (obj.transactionType === 'PAYMENT') {
            return 'receivedAmount is required for PAYMENT transactions';
          }
          return 'Invalid value for receivedAmount';
        },
      },
    });
  };
}