Custom exception for nestjs validation errors. It uses default error message transform from nest.js. You can also configure this.

validation.exception.ts

import { BadRequestException } from '@nestjs/common';
import { ValidationError } from 'class-validator';
import { iterate } from 'iterare';

const VALIDATION_ERROR = () => 'There are validation errors';

export class ValidationException extends BadRequestException {
  code: string;
  errors: string[];
  constructor(errors: ValidationError[]) {
    super(VALIDATION_ERROR());
    this.code = VALIDATION_ERROR.name;
    this.errors = this.flattenValidationErrors(errors);
  }
  private flattenValidationErrors(validationErrors: ValidationError[]) {
    return iterate<ValidationError>(validationErrors)
      .map((error) => this.mapChildrenToValidationErrors(error))
      .flatten()
      .filter((item) => !!item.constraints)
      .map((item) => Object.values(item.constraints))
      .flatten()
      .toArray();
  }
  private mapChildrenToValidationErrors(
    error: ValidationError,
    parentPath?: string,
  ) {
    if (!(error.children && error.children.length)) {
      return [error];
    }
    const validationErrors: ValidationError[] = [];
    parentPath = parentPath
      ? `${parentPath}.${error.property}`
      : error.property;
    for (const item of error.children) {
      if (item.children && item.children.length) {
        validationErrors.push(
          ...this.mapChildrenToValidationErrors(item, parentPath),
        );
      }
      validationErrors.push(
        this.prependConstraintsWithParentProp(parentPath, item),
      );
    }
    return validationErrors;
  }
  private prependConstraintsWithParentProp(
    parentPath: string,
    error: ValidationError,
  ) {
    const constraints = {};
    for (const key in error.constraints) {
      constraints[key] = `${parentPath}.${error.constraints[key]}`;
    }
    return Object.assign(Object.assign({}, error), { constraints });
  }
}